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An Overview on Hair Porosity

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, 1st 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 5th 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.

 

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