Scientific Blog Article

Although it seems to be common sense and even routine to some consumers to use sunscreens to protect the skin from the harmful effects of the sun, many still do not use any sunscreens in America.  This is especially true in the BIPOC (Black, Indigenous, and People of Color) community.  As the demography in USA has become more diversified over time, many cosmetic brands have recognized the needs of consumers of diverse skin tones.  In recent years, there has been a push to wear sunscreen for this BIPOC demographic.

Among many reasons for the lack of use of sunscreens in this demographic, aesthetics and safety of sunscreen products are most worth noting.   For decades, organic sunscreens have been dominating the sunscreen market. They could be irritating to sensitive skin and sometimes sting the eyes.  There has been a shift in recent years to the use of inorganic UV filters due to several reasons:

1. Mineral based ingredients are deemed to be inert, sustainable, and well associated with personal wellbeing.
2. ZnO was approved in 2016 as a safe and effective sunscreen active in EU
3. More importantly, TiO2 and ZnO are the only two actives assigned with GRASE status by FDA in its 2019 proposal¹.

However, formulating mineral sunscreens for consumers with dark tone, especially skin types V and VI on the Fitzpatrick scale, has remained a challenge. As it can be imagined, the major challenge to consumer acceptance is whitening or white cast on skin after application. This is because inorganic UV filters are particulate materials with high refractive index, and thus, can scatter the visible light strongly.

Although material technology has much advanced to allow TiO₂ and ZnO particles to be made as small as 10 – 20 nm and highly transparent on light skin types, whitening and/or bluing on very dark skin remains problematic for sunscreen formulators.  Below, will review a few formulating strategies for mitigating this undesirable side effect.

Use ZnO only

ZnO has a refractive index of 2, much lower than rutile TiO₂ which has a refractive index of 2.7. According to Mie’s theory on scattering, light scattering by ZnO is just about one third that of TiO₂, meaning it is much more transparent. Use of TiO₂ even at a low level could spoil the aesthetics. Therefore, it is imperative to use ZnO only for dark skin tones.

There are many grades of ZnO powder on the market with primary particle sizes in the range of 20 – 300 nm. Obviously, the smaller the size, the higher the transparency. For dark to very dark skin tones, a primary particle size in the range of 20 – 30 nm should be used.

ZnO is a moderately effective UVB sunscreen active, and thus, is often needed at very high level (15 -25%) to achieve SPF 30 or higher.  Such high use level presents another reason why a very small particle size must be chosen to maintain high transparency.

There are many ZnO-only sunscreen products marketed for consumers with dark skin types especially African American. One example is On-The-Defense Sunscreen SPF 30 from Eleven by Venus Williams. It contains 25% ZnO and claims “Sheer mineral sunscreen that melts onto skin, leaving a semi-matte, non-chalky finish.’

Disperse ZnO powder well

Just finding a ZnO with a small primary particle size does not mean a complete solution yet.  ZnO particles at this size scale have a very large specific surface area and surface energy and tend to aggregate heavily.  In reality, what really interact with the light are the aggregates or even agglomerates.  Therefore, proper dispersion to remove or minimize the population of large aggregates is important. Keep in mind, a small portion of large particles play a significant role in scattering visible light (whitening) due to their relatively large mass.  While dispersing ZnO with high-speed mixer or homogenizer may be sufficient for skin type I to IV, milling ZnO powder using a bead mill is necessary for higher transparency requirement.  In the absence of an efficient mill, the use of a ZnO pre-dispersion is a simple and effective approach.

Mitigating Whitening/Bluing

At high use level, ZnO will show some whiting on skin types V and VI even when it is very fine and well dispersed.  Moreover, even if the whitening is made unnoticeable, scattering of light in the range of 380 – 450 nm cannot be avoided, leading to bluing.  To mitigate the whitening/bluing and make sunscreen blend into dark skin well during application, pigments of warm colors can be used, as follows:

1. Red iron oxide pigment

The red color of typical iron oxide pigment used at a level of 0.2 – 1.0% is able to neutralize ll the whiteness and bluing of ZnO sunscreen. Many mineral sunscreens tinted with red iron oxide are available on the market and are marketed for ethnic skin style.  However, red iron oxide pigment is highly opaque, and its texture on skin can be chalky. When it comes to skin type V and VI, the finish with such pigment just cannot be as natural as consumer would expect.

2. Transparent iron oxide pigments

Transparent iron oxides are an improvement from standard iron oxide pigments and were initially developed for varnish formulation. They typically have a primary particle size of < 30 nm and are as transparent as nano ZnO. Boots Co. PLC first disclosed the use of nano red iron oxide in inorganic sunscreen formulation in the early 1900s². A few premium brands started to use both transparent red and yellow iron oxides in their daily wear sunscreen products since the mid-1990s. However, the use of such pigments remained very limited to this day.  In addition to high cost, one technical hurdle is that transparent oxides are very difficult to disperse. With this in mind, I highly recommend the use of a pre-dispersion.

Typically, 0.2 -0.5% of transparent red is sufficient in an all-ZnO sunscreen formulations.  Because dark skin can have different undertones (red, yellow or grey, etc.), a combination of transparent yellow and red iron oxides provides a more complete solution. At this use level, the transparent iron oxides impart almost no texture to the skin, and the finish is completely natural.

3. Use of Earth tone or dark pearl pigments

The basic optical principle of using Earth tone pearl is similar to using iron oxides.  As we know, pearl pigments often refer to mica with layers of metal oxide coating.  They usually have good transparency, especially when the substrate is highly pure synthetic mica.  As a result, its finish on the skin can be much more natural than a typical red iron oxide pigment.

It is preferred that pearls have red iron oxide as coating and that their particle size be below 15 microns. Any larger size may generate a pearlescent sheen on skin that will be deemed unnatural.  Typical use level is about 0.1- 1.0 %.  For very dark skin, grey or dark pearl pigments with a coating of black iron oxide or a combination of red and black iron oxides can be used at a level of 0.05 – 0.5% for further adjustment.

Like transparent oxides, a blend of Earth tone pearl and dark pearl pigments will provide a good balance for dark skin types with various undertones.  Formulators at Kobo Products applied this technology to its 4 in 1 Multi-Purpose Sunscreen Cream and won CEW Award in 2019 for the category of Ingredient and Formulation³.

4. Use of SPF boosters

The direct way to reduce whitening is to reduce the use level of ZnO.  It can be done by selecting the right SPF boosting agents.  Below are some strategies presented in the 2015 Sunscreen Symposium⁴. Here are a few highlights:

a) Film former: This technology is well known in our industry. Film formers can be oil soluble, water soluble or water dispersible (like latex). Many have been shown to boost SPF by 20% or more.

b) Antioxidants/anti-inflammatory: Many of them are proven to suppress the generation of erythema and can boost SPF very effectively.

Conclusion

Formulating mineral sunscreens for skin types IV to VI requires special considerations for very high transparency. An all zinc formulation should be the first consideration. The use of transparent oxides, and a blend of Earth tone pearl pigments can help to further reduce the whiten and/or bluing of sunscreens on dark skin tones and make them blend into skin more naturally.

References

1. https://www.federalregister.gov/documents/2019/02/26/2019-03019/sunscreen-drug-products-for-over-the-counter-human-use
2. NA Fardell et al., EP 0616522: Sunscreen compositions
3. https://www.cew.org/award/4-in-1-multi-purpose-sunscreen-cream/
4. Y Shao et al., Practical tools for boosting sunscreen efficacy, Sunscreen Symposium 2015

Acknowledgements

The author is grateful to Tatyana Tabakman and Cheres Chambers for insightful and helpful discussions.

Dr. Yun Shao joined Kobo Products Inc. in 1996 and currently serves as the vice president of R&D.  He has over 20 years of experience in micro TiO₂ and ZnO development and in inorganic sunscreen technology and regulations.  He is also experienced in pigment surface treatment, wet grinding, specialty cosmetic ingredients, color cosmetics and global cosmetic ingredient regulations. He has presented his work in various scientific conferences including IFSCC congress and FLSCC Sunscreen Symposium.  Dr. Shao holds 8 patents. He has co-authored several chapter books and technical papers on surface treatment and inorganic sunscreen formulations. Dr. Shao earned his Ph.D. in Polymer Chemistry from Rensselaer Polytechnic Institute and his B.S. in Applied Chemistry from University of Science and Technology of China.  He is the founding member of Chinese American Cosmetic Professional Association and the President during 2011-2012. He is also member of Society of Cosmetic Chemist and Chinese American Cosmetic Professionals Association and Tristate CACS. Dr Shao joined the NYSCC Scientific Committee in 2020.

Formulating cosmetic products presents many challenges, ranging from regulations, product safety, performance, aesthetics, consumer demographic trends and claim substantiation, in addition to media scrutiny, etc.  To be a successful formulation chemist, one must toggle many priorities with limited resources of time and money, while maintaining market launch timing.  In this blog, a few of the selected challenges will be discussed.

Every Ingredient Should Have a Function.  A formulation chemist should understand the structure-property relationship and the role of each raw material in a formula.  Raw materials are tools for creating formulation options and contributing to tactile sensory, stability and efficaciousness of the formulation.  There are many cosmetic ingredients with multiple functions, providing benefits that meet consumer demands.  By understanding the ingredient function and interactions in the complex composition, chemists can develop better formulation strategies.  At times, a formulator would be asked to “tweak” an existing formulation in order to replace an ingredient in response to a supply chain issue, regulatory constraints or to meet some sensory needs requested by marketing or consumers.  Simply piling ingredients into a formula does not always provide a solution to the problem.  In fact, it can backfire and create instability, or other unwanted issues.  It is important to be familiar with the latest raw material technology by developing long-term partnership with strategic teams (both internal and external contacts).

How to Knockoff a Cosmetic Formula?¹ One way to quickly become familiar with a cosmetic formulation is to “knockoff” (or duplicate) an existing formula.  Perry Romanowski published a 10-step strategy to essentially “reverse engineer” a competitor’s formulation.  This is by no means to simply create a “me-too” product, but to thoroughly understand formulation strategy and applications of raw material technology developed by competition.  It should serve as a good practice point for a novice and sometime even a seasoned formulator.  Again, the key points in Perry’s method are to (1) understand raw materials used in a formula by studying its full ingredient list (FIL), (2) read competitor’s patents and publications, and last but not least (3) create, revise and test prototypes, until the desired aesthetics are obtained.

Formulating Existing Formulation Platform.  As mentioned, a cosmetic formulator could be asked to “reformulate” an existing product formulation.  This is typically for continuation of a franchise with small modifications to the marketed formula, or a product launch with new claims, albeit based on existing formulas.  This approach can, for the most part, save time and resources on efficacy and safety testing, in addition to minimizing the potential risks from regulation and/or right-to-market.  Tony O’Lenick describes, in his many publications, “controlled modifications” of existing formulation. It is achieved by: ² (1) minimally disruptive technology, and (2) functional formulation.  The first approach uses low concentrations of polymeric surfactant(s) to alter aesthetics of existing formulation.  The second strategy pertains to raw material replacement in a formula, i.e., replacing raw materials based on how they function in the formulation.   For certain formulation types, especially mass-market products, it is also imperative to make certain of cost effectiveness for the final formulation.

Developing New Formulation Chassis.  This brings the most challenging and rewarding experience for a formulator, i.e. to create a brand new formulation chassis with a new formulation composition that gives rise to new and enjoyable consumer use experience.  However, the challenges for formulators exist in many areas: (1) developing a stable formula with a plausible right-to-market, and more excitingly, new patent opportunities in the IP landscape, (2) meeting the microbiological, safety and regulatory requirements for the specific product launch markets, (3) achieving efficient scale-up production from laboratory bench experience, and for sustainable business sake, (4) meeting the consumer demographic trends and marketing needs, including claim substantiation and consumer communication, etc.  Due to these multifaceted challenges, this type of formulation is typically managed as a longer-term research project.

Product Performance and Sustainability from a Formula Perspective.  Long before the pandemic of 2020, the personal care industry has seen the rise of “clean beauty” demand from consumers, while the pandemic seems to have accelerated this demand.³  By definition, “clean beauty” product formulation requires the use of safe and non-toxic ingredients with proven efficacy.⁴  To take it further, we shall take into consideration sustainable development, in order to counteract global warming and environmental changes.^4,5  What does it all mean for a cosmetic formulator?  It begins with selection of bio-based, renewable ingredients with respect of biodiversity and societal equality, and minimizing the use of fossil-based, non-renewable raw materials.  During formulation stages, one must also bear in mind the potential water usage to minimize the water footprint, and incorporation of as much as possible energy-efficient process for scale-up during production.⁶

Conclusion  

Cosmetic formulation has the most exciting challenges in combining science and art in response to the unmet needs from consumers.  A formulation scientist is an artist that creates new textures and influences the sensory perception of the customers.  In this ever-changing world of cosmetic and personal care industry, formulators are the primary driving force of technology and innovation.  No matter what formulation challenges at hand, product performance and sustainability will undoubtedly be the future of cosmetic formulation.

Acknowledgements

The author would like to thank the kind review and comments from Giorgio Dell’Acqua, Hani Fares, Ben Blinder, Howard Epstein, Hy Bui, Ryuji Hara and Ronni Weinkauf.

References:

1. Perry Romanowski, https://chemistscorner.com/
2. Tony O’Lenick, http://www.scientificspectator.com/tony-olenick-compilation-of-articles/
3. NYSCC “At Home Live Series – Clean Beauty”, November 19, 2020.
4. Giorgio Dell’Acqua, Clean Beauty – Beauty Horizons, December 15, 2020 https://digital.teknoscienze.com/beauty_horizons_1_2020_ww
5. L’Oréal Sustainability Commitment for 2030. https://mediaroom.loreal.com/wp-content/uploads/2020/06/EN_Booklet_LOreal-for-the-Future_2020.pdf
6. L’Oréal Product Environmental & Social Impact Labelling Methodologies. https://www.loreal.com/-/media/project/loreal/brand-sites/corp/master/lcorp/documents-media/publications/loreal-pil-methodologie-en01.pdf

Dr. Catherine Chiou holds a BS degree in Chemistry from National Taiwan University and a Ph.D. in Bioinorganic Chemistry from the University of Minnesota.  Catherine’s NIH Postdoctoral fellowship training in Synthetic Chemistry took place at Harvard University.  Her first industrial position was with Unilever Research US in the laundry bleach research program and machine dishwashing detergent research, including I&I applications.

Catherine began her career in cosmetic field at L’Oréal USA in 2001 in the DIMP (International Raw Materials Department).  She worked on all aspects of “innovative raw material” functions, including scouting for new supplier innovations, and managing supplier relationships.  In addition, Catherine took on a role within the PCPC INCI Committee.

Catherine is currently an Associate Principal Scientist at L’Oréal USA in the Cosmetic Application Domain, focusing on developing skin cleansing and makeup removing technologies.  Prior to the current position, she has worked in the skin care research and innovation lab as a senior formulator, contributing towards development of platform technologies and several global launches of skin care treatment products.  She is an inventor for more than 20 US and international patents.

How Many Languages Does our Skin Speak? A fresh look at what it can it teach us in terms of innovation if we listen.

Inflammation is Just the Beginning:

Inflammation has garnished the attention of mainstream headlines for the past 20 years and has certainly taken center stage describing and managing the current virulence of the pandemic.  With terms like cytokine storm, pre-existing conditions and co-morbidities, what have we learned and what we still need to learn to properly manage the ill effects of inflammation and its impact on health is astounding.  As a biologist, I adopted the general tenant that inflammation is the root of all evil when it comes to aging and disease, particularly in the skin.  Whether its role is in normal aging from a subclinical perspective or pathological in nature in an acute verses chronic situation, inflammation seems to be a rate limiting step or first domino to fall for most underlining causes of both intrinsic and extrinsic aging processes in our largest organ the skin.  Even in the Covid-19 era, we are seeing persistent skin rashes documented post infection, why?  What are we doing right and what should we be doing different?

The good news is that we seem to understand inflammation from a mechanistic point of view.  How reactive oxygen, metals, lipid mediators, enzymes, transcription factors, temperature, microbes and sun play a role in skin inflammation is well documented.  The disconnect here is that we in the industry of cosmetic science have decided to treat the sources of inflammation as individual events rather than a consortium of cumulative ever changing processes designed to mute our first line of defense.  This is akin to putting a lock box around a fire alarm verses reducing existing fire hazards.

In this regard, let us not loose site of the purpose of inflammation, which is to alert and respond to acute threats to homeostasis or skin balance.  Every level of our biological organization has its own cadence on how homeostasis is maintained and managed over time.  From a molecular level, through soluble cytokines (the language of our cells) all the way to behavior responses, evolution has afforded us a great deal of redundancy in this regard, all culminating to the ultimate goal of maintaining health and balance.  In what follows, I hope to serve up a fresh look at how we as skin care technology providers can approach new product designs and formulation innovations that not only address acute disturbances in skin but may ultimately change the way we look and feel about our skin and ourselves as a whole.

The Skin as a Sensory Organ:

The best part of focusing on the skin is that it does so much for us in terms of our survival, health, and our ability to adapt to the environments we find ourselves in on a daily basis.  Furthermore, the epidermis and some of the cell types that reside in it (melanocytes, Langerhans-like phagocytes) are embryologically derived from ectoderm which also gives rise to our nervous system proper.  This is a profoundly underappreciated opportunity as our skin has all of the “gear” needed to effectively communicate with the nervous system as well as the endocrine system and vice versa.   In this regard, we need to integrate the fact that our neural, endocrine, immune, skin microbiome and skin biology are all interlaced and cross talk every moment of our existence.  The ability of our skin to react to its environmental threats through inflammatory processes has opened a window into a world that is vastly more complex and interactive.   It requires a master’s degree in linguistics to hear all the talk between keratinocytes, immune cells, hair follicles and sweat glands and melanocytes.  As a result, this conceptual understanding opens up targets that not only affect the skin proper but our behavior as well.  What if we could understand the autonomic picture our brain has of our skin?  I believe we would see numerous snap shots of skin grafts unique to one another, painted by skin thickness, pH, lipid structure, water content, hair follicle density, immune residence and microbiome attendance.  Could we re-focus our formulation efforts in terms of sensory to be more inclusive of these micro environments and their associated biology?  Could we change the way our brain “sees” our skin?

Behavior is driven by how we perceive our surroundings.  Our skin is considered a neurosensory organ much the same way other species use antennae or chemoreceptors to “see” their environment as demonstrated by insects and snakes respectively.  Our skin senses electromagnetic radiation, temperature, chemicals, pH, biological insults, and subtle changes in our microbiome.  It also knows when there are sub clinical changes in chemistry as well as disruptions in barrier and wounding.  All of these stimuli we cannot see with our other senses unless they are out of sync or control.  We tend to focus more on sight and sound as an organism.  Why then do we ignore the largest sense organ we possess when it has so much to say?  More so, all of these stimuli are transmitted to the brain (consciously or unconsciously) and to the surrounding cells and tissues simultaneously, thus having an impact not only on our behavioral responses but on our epidermal biology, our immune and endocrine systems.  Furthermore, the reverse is true.  The brain and adrenals along with the immune cells talk back.  A fundamental requirement for communication is that more than one entity needs to deliver information to another that can receive and react to it.  How cool is it that whatever stimuli the skin observes it is translated via different systems that act in concert to maintain homeostasis and dictate behavior.  As formulators and inventors, the next level of innovation will come from exploiting these lines of communication.  Recall how simple the Wright brother’s solution to flight was compared to the latest version of air travel today.  You will most likely not be in a position to imagine a jet airliner if you never saw the Kitty Hawk.

Immune System Integration:

If things were not complex enough, we need to consider the immune system and all of its abilities and functions as a driver of skin health.  The marvelous thing about our immune system is that it is driven not just by genetics but also by environmental pressures we expose our body to on a regular basis.  The immune system adapts and learns and has a periodicity that is defined by age and time.  Our immune functions start out naive then grow, mature, plateau and decline throughout our lifespan.  Furthermore, our immune system is organized into two systems (innate and adaptive/learned) that together synergize in function.  It even has its own residential lymphoid cells called skin associated lymphatic tissue or SALT which supervises and coordinates your interactions with all things non-self.  From that organization it specializes in various modalities of responses that are classified into 3 groups depending on the type of initiation involved and cytokine profile released into the milieu along with contributions from epithelial cell derived cytokine signals such as IL-33.  For example Type I immunity is relegated to intracellular threats (viruses and parasites) and the production of IFN-g and/or TNFα.  Type 2 immune responses are in ordinance with itch and are caused by harmful substances driven by the secretion of IL-4, IL-5 and IL-13.  Type 3 immunity is specific to extracellular bacterial and fungal infections and characterized by the production of IL-17 and IL-22 cytokines.   It is interesting to note that the cytokine profiles of each type of immunity dictate a specific ordered response by immune tissue, but they also modulate sensory perception and behavior, another key component to our overall host defense arsenal.  For example, IL-33 release from keratinocytes in a compromised epidermal barrier can stimulate local neurons to become hypersensitive and hyper-excitable, thus releasing neuropeptides like substance P and CGRP, which then feedback on the very same keratinocytes to increase their proliferation in an effort to restore the compromised barrier.  As a result, the hypertrophy can further disrupt epidermal differentiation, trap bacteria and acne and/or folliculitis ensues respectively in affected sebaceous gland canals and hair follicles respectively.  Furthermore, antibodies to IL-13 and IL-4 (type 2 immune responses) reduce barrier inflammation which reduces itch in AD stuffer’s.

By grouping immune type cytokine profiles together along with their temporal expression patterns that includes initiation, plateau and resolution makes for a more precise technology development strategy in this regard.

A Systems Approach to Understanding:

It is an interesting to note that the nervous system and its functions rely on afferent signals (sensory neurons and their associated stimuli) to understand its place in the environment, whereas the immune system also “senses” our body’s interactions with our surrounding through more of a military surveillance strategy of touch, chemical codes, catabolism and synthesis.  Furthermore, the brain and its neurons are fixed in place converting chemical signals into electrical and back again at supersonic speed whereas the immune system is both static and dynamic adapting and learning at a significantly slower pace alongside the brain.  It evolves and grows.   The interplay between both of these systems tends to out rank the local tissue signals in which they reside. A linear approach to skin therapy has focused primarily on the residential populations of the skin with a peripheral mention of the other systems as secondary is like only listening to one side of the conversation.  Leveraging a systems approach to new skin therapeutics and personal care technologies could lead to significant transformational innovations in product development including new categories of skin care.

How does all of this work and where are we headed? 

Advances in sensory biology (specifically itch and pain) have elucidated novel mechanisms that arose from our understanding of inflammation.  Itch and pain are great examples of behavior changes as we have all experienced both.  What if by understanding how to modulate these behaviors we could apply these same strategies to resolve dry skin, alter tone and texture, improve radiance and create the de-novo synthesis of endogenous beneficial molecules such as vitamin D, melanin and keratin.  Furthermore, what if we could take these strategies forward to build better nails and hair, modulate sebum quality and quantity and even provide some level of subconscious behavior that could help you lose weight, reduce stress or just be happier?  We spend a lot of time and energy trying to reduce acne which has significant behavior ramifications especially in teenagers, when in actuality, if we could just reduce the erythema in a timely manner, most of the terrible downstream problems would be better tolerated or ameliorated such as post inflammatory hyperpigmentation and self-esteem related syndromes.

Melanocyte Biology Reimagined:

Since melanocytes are the focal point of Post Inflammatory Hyperpigmentation, they could be considered the “conductor” of the cross talk between residential skin cells, neurons and immune processes.  These cells that act as a UV detectors in our skin may in actuality have the ability to sense and focus on other stimuli.  They are of course derived from the same primordial soup as neurons.  If true, these master regulators would need to communicate with and receive signals from all cell types including neurons, macrophages, Langerhans cells and various lymphoid tissues (SALT).  Just like neurons, melanocytes convert energy to communicate.  Here melanocytes convert electromagnetic energy (UV and HEV) into relevant biological signals that initiate signal amplification and recruitment of multiple tissues to ultimately elicit a behavior change.  The same signaling molecules that have a role in the central and peripheral nervous tissue also have a role in cutaneous melanocytes. These include signaling pathways that include Wnt, bone morphogenetic proteins, endothelins, hepatocyte growth factor, fibroblast growth factors, and neurotrophins.

Applying the Concepts:

When afferent sensory neurons fire in our skin, they release neuropeptides in an efferent (reciprocal) manner that has its effects on melanocytes and immune cells simultaneously.  In other words, the skin is already reacting to the stimuli before the brain even gets the signal.  This is an important event as this profile of cellular signals creates a customized code of signals unique to the stimuli, very similar to the basic formula for how your brain remembers a memory.  If by understanding this profiling technic our body uses on the local level we could indeed teach our skin to react in different ways by nudging and modulating profile dynamics.

This concept is already in practice through the use of antibody therapy for psoriasis and atopic dermatitis (AD).  These antibody therapies work by interfering with the cytokine-induced pathways in neurons, important for intercellular conversations with local cytokines which then in turn modulates itch and inflammation.  The immune therapeutic Tofacitinib works through JAK inhibition thus reducing inflammation better than traditional broad spectrum anti-inflammatory strategies (systemic steroids).   Here the traditional modality of treating the source of the problem is over ridden by muting the signal that helps propagate it.  Additionally, this neuron targeted approach is also supported by the observations that patients with inflammatory (AD) experienced resolution of inflammation in body parts that experience nerve loss.  What are we to conclude from this? Chronic inflammation requires communication with the nervous system.

Integration of the Skin Microbiome:

Peeling back yet another layer of the onion, we need to include our newfound tribe the skin microbiome.  In collaboration with the gut microbiome, these two tribes have considerable influence on everyday life as it relates to well-being and health.  If you wonder of their overall purpose, it lies in their ability to adjust tolerance and direct the necessary “activation energy” needed to amplify inflammation, over and above the status quo.  Think of it as immune exercise or conditioning.  The diversity of microbes in and on our body translates and cross-trains all the different biological conversations between the skin epithelia, immune cells and processes along with the existing neural architecture. The “chatter” establishes a level of readiness.  It results in an overall host defense that is primed and semi-activated to address danger and invasion.  When microbiome diversity is lowered or dominated by a few select species, the response is detrimental by two-fold.  One, it allows for re-colonization of the skin by opportunistic invaders which may not be pathological at normal levels but create that cytokine profile or “storm” that trips the balance of cross talk between all the players resulting in an increase in entropy of the whole system.  Chaos, isn’t that what we all work so hard to control?  Two, the low diversity establishes a lower state of readiness and as result the conversations become quieter and limited leaving the health of the skin vulnerable to imbalance and thus, putting negative pressure on behavior.  Can we blame our little friends for our actions and thoughts?  Absolutely!  Just as folks with AD, psoriasis, irritable bowel syndrome and Crohn’s disease.

In closing:

As a result of all this biological chatter we have order and purpose.  It is exciting to see how fundamental understanding evolves.  The integration of multiple languages into a new one with higher purpose, efficiency and meaning is an evolutionary learning process.  To naively think we understand the language of our biological complexity is limiting our potential.  We must integrate and transcend across the mechanistic understanding and incorporate a multi-disciplinary approach to new concepts and ideas.  We need to explore new ways to achieve desired responses and ultimately behavior that favors well-being for all ages and health both physically and mentally.  I can’t help but wonder how many times we find ourselves enjoying a good meal, listening to our favorite music or being with friends and family that creates a sense of well-being that is most grounded.  Isn’t that what you would like to have in a product?  These feelings can’t be solely due to cerebral contentment, you have billions of other contributing opinions looking out for the same sense of well-being.  It’s time to listen more intently to those conversations.  One could have a hard time arguing which system truly dominates the conversation and thus our behavior and as a result our health.  Let not your strategy and ideation be limited to just one language.

Inspiration was gleaned from the following references:

The Neuro-Immune Axis in skin Sensation, Inflammation and Immunity, Anna M. Trier et. al., J Immunol, 2019 May 15: 202(10): 2829-2835.

Melanocytes: A Window into the Nervous System, Mina Yaar, et. al. Journal of Investigative Dermatology Volume 132, Issue 3, Part 2, March 2012, Pages 835-845

Inflammatory Resolution: New Opportunities for Drug Discovery, Derek W. Gilroy, et. al., Nature Reviews /Drug Discovery May 2004, 401-416.

Michael Anthonavage
VP of Operations & Technology
Eurofins CRL Cosmetic Testing, Inc.

Michael Anthonavage has 20+ years of experience in personal care product development and a career spanning background in skin biology. Michael has extensive knowledge in product development and product design.  He specializes in R&D to marketing translation, including claims validation both in-vitro and in-vivo. He is an engaging public speaker and product technology advocate with an ability to marry complex ideas and concepts to various consumer needs. Michael is currently the VP of Operations & Technology at Eurofins CRL Cosmetic Testing, INC.  Michael’s previous positions have involved R&D leadership positions at Johnson & Johnson Consumer Products, Presperse and Vantage Specialty Chemicals.  Michael is currently on the NYSCC Scientific Advisory Board and has won a variety of industry awards for his contributions in research and product development.   He has a number publications and patents to his name and continues to be an influential speaker in the personal care, bioinstrumentation and skin testing arena.

Introduction

Human hair is characterized by several descriptors, some of which influence how the hair behaves and responds to cosmetic products.  Common descriptors include texture, density and diameter.  Porosity is another relevant descriptor of hair that merits further attention.  It is advantageous for the industry to consider aspects of hair porosity given the rise of customization in hair care.  Further, the industry has become increasingly more interested in textured hair care.  Individuals with textured hair, hair that is naturally wavy, curly or coily, are more likely to have more porous hair than individuals with straight hair (1). Hair porosity resonates with textured hair consumers, especially considering that moisture and breakage are top concerns among this demographic (2).  The objective of this blog is to present a primer on hair porosity and its relevance to the cosmetic chemist and consumer alike.

Overview of Hair Porosity

Hair porosity describes the extent to which hair absorbs and retains water, products and treatments based on the integrity of the cuticle.  Porosity can be influenced by both genetics and hair grooming practices to varying degrees.  This blog will focus on the extremes of low and high porosity, but it should be noted that a mixture of low, normal and high porosity hair fibers can certainly exist in a head of hair.  Additionally, porosity can vary along the length of the hair fibers.

Normal or medium porosity hair absorbs and retains water reasonably well; hair can absorb 75% of the maximum amount possible within 4 minutes (3).  Normal hair is also receptive to chemical treatments such as bleaches, colorants and relaxers, and the results are generally predictable.

In low porosity hair, the cuticle layers are reinforced and lay flat leading to hair that is more resistant to water and chemical treatments.  From a consumer perspective, this is realized if  1.) the hair takes a significant amount of time to wet and dry, 2.) products build up easily on the surface rather than absorbing, 3.) protein treatments yield a stiff feel, and/or 4.) chemical treatments are less effective than expected.

In high porosity hair, the cuticle is compromised by configurational, mechanical and/or chemical stresses.  Textured hair represents a good example of how configuration can influence porosity.  Curls and coils are characterized by twists that lead to cuticle lifting at various points along the fiber, and this is more prevalent in the more elliptical hair fibers characteristic of individuals of African ancestry.  Mechanical stresses from daily grooming practices such as combing, brushing and hygral fatigue from repeated wetting (swelling) and drying (deswelling) can damage the cuticle over time, thereby exposing hydrophilic areas.  Chemical treatments such as oxidative colorants and ultraviolet radiation can affect hair porosity by oxidizing the protective surface lipids (3,4).

From a consumer perspective, high porosity presents as hair that absorbs water and dries quickly, maintains a dry feeling, experiences excessive frizz and breaks easily in some cases.  While high porosity hair quickly absorbs water, it also loses water quickly. The effects of chemical treatments are also accelerated and inconsistent in some cases, which can lead to damage.  For example, porous hair accepts hair colorants faster and the treatment can result in a cooler tone than that observed on less porous hair (5).

Consumer & Technical Methods for Hair Porosity

Select consumer and technical methods used to evaluate hair porosity are highlighted below.  Simple qualitative methods such as the Float Test and Spray Test have limitations but can potentially give a general idea under controlled conditions.

 – Float test: A qualitive assessment of porosity is made based on how quickly a clean hair fiber sinks when placed in room temperature water.  If the fiber more quickly sinks to the bottom, then it is porous.  If it floats over time, then it is likely low porosity.

– Spray test:  A qualitative assessment of porosity is made based on the behavior of water when sprayed on clean dry hair.  High porosity hair should adsorb the water more quickly than lower porosity hair, which would instead have visible beads of water and a longer dry time.

 – Dynamic Vapor Sorption (DVS) (6): The weight of hair is recorded as a function of increasing or decreasing humidity.

 – Gas Adsorption & Pore Size Analysis (7): Hair samples are subjected to nitrogen adsorption followed by mapping of the distribution and sizing of pores.

 – Fiber Swelling: The dimensions of a hair fiber are measured as a function of exposure to water. 

Hair Care Considerations by Porosity

The key concern for low porosity hair is hydrating the hair.  This can be facilitated with the use of a steamer, which simultaneously opens the cuticle with heat and infuses water vapor into the hair (8).  The steamer can be used to aid penetration during deep conditioning or to revitalize and moisturize hair as needed during styling.  The Q-Redew^™ Handheld Steamer has become a quite popular tool.  Additionally, neat or formulated light-weight polar saturated oils can slowly absorb into the hair (1).  Rele et al demonstrated that coconut oil supports hair moisture retention and fortification by reducing water sorption and hygral fatigue (9).  Products that are less likely to penetrate the hair and result in buildup, i.e. some proteins, butters, etc. should be avoided in significant amounts, while those that contain humectants such as glycerin can be useful.

As the key concern for high porosity hair is moisture retention, consumers with this hair type benefit from sealing the hydrated hair with oils.  Consumers with textured hair frequently employ product layering to help retain moisture (in addition to styling).  This is referred to as the LOC or LCO method, in which the hair is hydrated with liquid or leave-in conditioner (L), followed by an oil (O) to seal the hair and then a creamy moisturizer/styler (C).  Polyunsaturated oils like avocado oil reportedly work best for high porosity hair.  While scientists have demonstrated that perceived hair moisturization does not correlate with actual hair moisture content (8,10), this method warrants attention given the satisfaction expressed by consumers.  It is plausible that the perceived improvement in “hair moisture” resulting from product layering techniques is due to the combined influence of at the least some of the following variables on the modification of the hair’s tactile properties: presence of product on the surface, oil penetration, and actual moisture content or localization.

In addition to sealing the hair with oils or product layering, high porosity hair can benefit from protein treatments.  Proteins can fill the voids of a compromised or lifted cuticle via film formation and penetration into the fiber. Further, products with significant levels of humectants should be avoided depending on the climate.

While there are marketed products that target hair porosity concerns, efficacy data are not available to the greater scientific community.  This opens the door of opportunity for the technical community to link technical capabilities such as the aforementioned methods with compelling data-backed product/ingredient stories.

Conclusion

As personalization in cosmetics/personal care continues to grow, the industry could benefit from further considering hair porosity.  Opportunity exists to further explore the distribution of hair porosity types and the link between porosity and CMC lipids, protein content, etc. beyond the current understanding.  Further research into this parameter could lead to ingredients, formulations, test methods, styling implements, and communications better tailored to address various hair porosities more effectively.  Linking consumer perception and practices with appropriate technical principles will be useful in meeting the needs of diverse hair types.

References

1. Davis-Sivasothy, The Science of Black Hair (Saja Publishing Company, Texas, 2011), pp. 47-50, 78-91.
2. Texture Media LLC. Texture Trends Consumer Study 2018.
3. Dawber. Hair: its structure and response to cosmetic preparation, Clinics in Dermatology, 14, 105-113 (1996).
4. Syed. Correlating porosity to tensile strength, Cosmetics & Toiletries, 117,11, 57-62 (2002).
5. M. Frangie, L. Barnes, and Milady. Milady’s Standard Cosmetology Textbook, 1^st ed. (Cengage Learning, Massachusetts, 2012), pp.630-631.
6. Evans, “Adsorption Properties of Hair,” in Practical Modern Hair Science, T. Evans and R. Wickett. Eds. (Allured Business Media, Illinois, 2012), pp. 333-365.
7. Z. Hessefort, B.T. Holland, and R.W. Cloud. True porosity measurement: a new way to study hair damage mechanisms, J. Cosmet. Sci., 59, 263–289 (2008).
8. Schmid, H. Hair care appliance and method of using same. U.S. Patent 8,136, 263, filed August 21, 2008, and issued March 20, 2012.
9. S. Reles and R.B. Mohle, Effect ofmineral oil, sunflower oil, and coconut oil on prevention of hair damage, J. Cosmet. Sci., 54, 175-192 (2003).
10. Davis. Moisture vs. Moisturization: Understanding the Consumer Benefit, P&G Beauty Care Presentation, TRI 5^th International Conference on Applied Hair Science (2014).

Dr. Amber Evans is a cosmetic industry professional with over a decade of experience and expertise in the science of hair and skin care.  In her current role as Senior Manager of Product Development at Moroccanoil, she is responsible for driving the development of high-quality innovative hair & body care products for the successful global brand.  She previously worked at as a development scientist at BASF Corporation, where her contributions spanned multiple market segments, including hair, body and oral care, and the technical areas of innovation and claims testing over eight years.

Dr. Evans earned a Ph.D. in Pharmaceutical Sciences (Cosmetic Science focus) from University of Cincinnati and a B.S. in Chemistry from North Carolina Agricultural & Technical State University.  She has conducted extensive research into the influence of water hardness on hair and has contributed to initiatives including upstream research for hair colorants, hair conditioner formulation and clinical testing for skin/shave care applications at The Procter & Gamble Company.  She has also authored hair care research publications, contributed content to NaturallyCurly.com, the leading resource for textured hair care, and featured on multiple platforms that support aspiring scientists and early career professionals.  As a mentor, active member of the Society of Cosmetic Chemists (SCC) and of the NYSCC Scientific Committee, peer reviewer for the Journal of Cosmetic Science and member of the Advisory Board for the University of Cincinnati Cosmetic Science Program, Dr. Evans is dedicated to influencing the progression of the cosmetic field.

Introduction

Light dances on the surface of special effect pigments before it bounces off angles to bend and blur lines with optical diffusion, creating depth, offering dimensionality, sheer luminous glow or a dazzling, eye catching sparkle. Used in everyday products across a wide array of industries such as color cosmetics, personal care, auto, paint and fashion, an effect pigment can display color, offer multiple effects, impart color travel as it reflects and refracts light through many angles. The chemistry and manufacturing process impact the unique visual performance of these special effect pigments but may not be as appreciated or understood compared to the end product’s desirable effects. Taking a closer look at the use of effect pigments in the beauty industry as their function and use allows for eyeshadows to take on properties offering intense color depth and a captivating sparkle, stunning gemstone effects in nail polishes and for highlighters to impart a soft focus contour on cheek bones.

The special effect pigment market has been forecasted to increase over the next 5 years due to high consumer demands seeking to continue personal care upkeep particularly within the nail and eye category as a result of Covid-19.   An evolution is not only seen regarding effect pigments usage through the years in cosmetic products to attain desired results, but also with an important transition to address sustainable platforms looking to safeguard global resources. These initiatives intertwine the beauty industry with heightened levels of innovation to support ethical and environmental objectives.

Intricate Composition

Special effect pigments, often referenced as pearlescent pigments, have manufacturing processes that are as dynamic as the product effect itself.  Visual properties are created with a starting base layer known as a substrate. Initial determination between a natural or synthetic substrate help to establish expected properties and unique characteristics when used in a product. Natural options include Mica, Kaolin, and Rayon. These ingredients are Generally Recognized as Safe (GRAS) and create similar effects to synthetic options such as fluorophlogopite, boron nitride, and glass flakes/borosilicates. Differentiation is demonstrated through optical impressions with the level of reflection, opacity, and interference offered.

Depending on the selected substrate and desired end use, the manufacturing process plays a critical role to yield the product consumers are accustomed to seeing in finished goods. Review of the process cycle used when mica is the substrate offers an opportunity to demonstrate the level of detail involved during development. The mined mica is coated typically with Titanium Dioxide or oxide metals during processing. This occurs when a base and acid are combined in a reactor used to calcine the substrate at variable high temperatures. Impurities are then filtered off, and the process is completed through blending. The thickness of the coating on the substrate directly determines elements of color and can offer interference effects when alternating layers of oxide metals are used or combined with transparent spacers to create optical variable pigments for color travel. Observed color effects are directly correlated to the thickness of the coating as it increases and decreases. The thickness of the coating impacts color development ranging from gold, red, violet, blue to green translating from 70 nm to 360 nm in measurement, respectively. Particle size of the effect pigment plays a critical role as well in the brilliance. Smaller sizes closer to 10 µm impart more of a soft texture matching a satin sheen coverage; larger sizes closer to 60 µm displays more of a dazzling pearlescent appearance; while an average micron size of 125 and above sparkle.

Enhancements

Effect pigments similar to iron oxides and dyes are not necessarily easy to add to formulas as it is dependent on the chassis composition. Stability, color shift, and undesirable payoff performance can be experienced by a formulator during product development as a result of polar hydroxyl groups with adsorbed moisture on the effect pigment.  Surface treatments on effect pigments whether physical or chemically added can address many common drawbacks to ease dispersion into formulas, improve outcome of stability and other unique benefits based on the chemical properties of the specific treatment used.

Sustainable Vision

Ethical and environmental concerns prompted many forward-thinking beauty organizations to create innovative solutions and restriction lists in response to negative aspects of the effect pigment supply chain. Focus on child labor, traceability, and environmental considerations are needed for a better tomorrow to keep our world beautiful more than just on the surface. As a result of these issues being uncovered, opportunities arose for alternative material solutions paired with philanthropic initiatives to give back to communities. As a result, demand to innovate in support of environmentally considerate substrates such as bio-based options were developed. Bio-based effect pigments look at upcycling to introduce cleaner alternatives with similar appearances and attributes especially compared to PET glitters. The ban on microplastics in recent years has exposed PET glitter due to their small size and inability to breakdown as they enter the environment and can end up on our dinner tables. Due diligence has spurred innovation on many levels as formulators seek new understandings to develop similar product effects and encourage consumer education in hopes to inspire mindfulness.

Formulating Tips

• Effect pigments should be incorporated carefully into batches and sweep mixing blade is recommended. It’s best to avoid particle size optimization with homogenizers as they are fragile materials, and it jeopardizes the effect of larger micron sizes when sheer force is applied. When the effect pigment surface is deformed the sparkle effect is reduced or no longer visible.
  Take time to understand the material’s specifications from the certificate of analysis (COA). For example, when formulating anhydrous formulas the oil absorbency and ingredient ratios determine ease of pourability, skin feel, and payoff. A balanced, high performing formula takes into consideration these aspects to make improvements and/or alternatively to select a surface treated option if a high effect pigment loading is required.
• Caution is recommended with composites that contain Ferric Ferrocyanide, Carmine or when used in a formula that will contain Avobenzone with Titanium Dioxide coated pigments as this will likely shift color and cause other adverse stability outcomes.
• Understand global regulations to ensure that each of the effect pigment constituents meet regulatory requirements and areas of use for distribution. Not all pigments are allowed in the eye area and micron size is another critical aspect to consider pending product positioning. Generally, special effect pigments for eye product have a micron cap at 150. While this can pose as a challenge to match prototypes there are other available options such as synthetic fluorophlogopite that do not follow the same particle size restrictions.
• Color matching should be done with colorants, iron oxides and dyes, then to use effect pigments to compliment. Higher usage levels of pigments should be used to achieve deeper, more intense tones and will offer a good base color to make it easier to shade match instead of being reliant on pearls alone where there is less color consistency. This technique promotes cost efficiency for a more economical approach to shade matching as well.

Conclusion

Special effect pigments have wide applicability to impart visually appealing impressions. The characteristic properties are heavily reliant on the chemical framework and manufacturing process implemented to determine desirable elements. The beauty industry counts on effect pigments for their role to enhance the color appeal, effects, and texture in finished goods. Even as much as the consumer looks for these alluring effects, sustainable platforms are necessary as awareness increases. Sustainability has invigorated innovation within this market that will hopefully continue to support technological advances with novel solutions.

References

1. Cramer WR. Hidden Secret of Effect Pigments. PCI Magazine, October 3, 2017 – https://www.pcimag.com/articles/102924-hidden-secrets-of-effect-pigments
2. Maile FG, Pfaff G, Reynders P. Effect pigments-past, present and future. Progress in Organic Coatings, 54 (3): 150-163, 2005
3. Special Effect Pigments Market Size 2020 Industry Demand, Share, Trend, Industry News, Growth, Top Key Players, Business Statistics and Forecast to 2026. Market Watch, October 8, 2020.

Acknowledgements

Frank Mazella, David Schlossman, and Yun Shao for inspirational talking.

Stacey House

Stacey is the Vice President of Research and Innovation at KDC/One’s East Coast R&D leading the talented teams at Acupac, Chemaid, Innovation Lab and Kolmar. Her strong team is focused on developing elevated, high touch formulas in categories spanning the personal care industry. Previously, she was the Director of R&D at Mana Products, Director of Applications at Kobo Products, and had also worked in Coty and Revlon’s R&D labs. She holds a patent on Low Viscosity Phenyl Trimethicone Applications and has written several published industry articles. Stacey graduated from Northeastern University with MBAs in Operations, Supply Chain, and International Business and received her Bachelors of Science degree at Rutgers University-New Brunswick.