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The skin’s outermost layer serves as a barrier to keep foreign matter out and to essential elements, such as moisture and water, in. Maintenance of this skin barrier is crucial to healthy functioning skin, while a damaged or diseased skin barrier is vulnerable to infection, irritants, and allergens. Furthermore, the loss of moisture often results in dry, flaky skin, which remains one of the most common and vexing of human disorders.1 Conversely, a healthy skin barrier means supple, younger, and less wrinkled looking skin without undue dryness—and the cornerstone of skin barrier regulation and repair is through the use of moisturizers.2

Of course, when it comes to moisturizers, the sky’s the limit. There are myriad different types of moisturizing ingredients, many of which have some level of research to support their value. So where do you begin when deciding on which type of moisturizing ingredient to choose? Let’s start with the stratum corneum.

The Stratum Corneum
The stratum corneum (SC) is the outermost layer of the skin, which is often thought of as just dead skin cells. The truth is that the SC is a highly dynamic layer of cells that is essential to maintaining skin moisture. The structure of the SC can be analogized as a brick and mortar configuration. The bricks are flat hexagonal corneocytes, stacked in layers. The mortar of the SC consists of natural moisturizing factors (NMF) and lipids. The primary function of NMF is to attract and bind water in order to maintain moisture homeostasis in the SC.3 The most prevalent single component of NMF is pyrrolidone carboxylic acid (PCA), a derivative of amino acids.4

Introduction To NaPCA
Not surprisingly, PCA can be found in some commercial moisturizers. The form of PCA typically is the sodium salt of PCA (NaPCA), which is also naturally occurring in the SC.5 Researchers have determined that PCA contributes significantly to the SC water binding capacity. Biologically, this property allows the outermost layers of the SC to maintain liquid water against the drying action of the environment.6

Of interest is the fact there is a significant age-related decline in the level PCA.7 Likewise, PCA is dramatically depleted in conditions such as psoriasis,8 and is also reduced as a consequence of washing with soap.9

NaPCA primarily functions as a humectant moisturizer in skin and hair care products, including gels, creams, lotions, shampoos, conditioners, lipsticks, and foundations. It is typically used in a concentration range of 0.2 to 4 percent. A humectant is a substance that often has a molecular structure with several hydrophilic (water-loving) groups. This structure allows humectants to attract and retain the moisture in the air nearby via absorption, drawing the water vapor into or beneath the surface. As a humectant, NaPCA helps keep the skin hydrated and may also help other topical skin care ingredients to perform better.

According to some skin care experts, when topically applied, NaPCA is able to mimic the NMF, which helps reduce signs of aging, such as lines, wrinkles, and dry skin. This results in a skin condition that is smoother, hydrated, and firm. Furthermore, the safety of PCA and NaPCA has been evaluated by the Cosmetic Ingredient Review (CIR) Expert Panel. The CIR Expert Panel concluded that PCA and NaPCA are safe for use in cosmetics and personal care products.10

Clinical Research On NaPCA
In one study,11 the medical and biological literature was reviewed with a focus on the role of PCA and NaPCA in skin, its metabolism, its functions. The study also included a summary of eight years of laboratory evaluation work carried out on creams and lotions containing PCA and NaPCA, assessed by biophysical and clinical methods. The results definitely demonstrated that PCA is a hydrating agent and that cosmetic preparations containing NaPCA improved the condition of dry skin in the short or long term. The mechanism of action was found to involve the metabolism and physiological role of PCA in stratum corneum.

Another study12 examined the efficacy of NaPCA. A product containing NaPCA was found to increase the water-holding capacity of isolated animal corneum. In a human trial, skin dryness and flakiness were assessed by trained assessors. Results were that NaPCA product was more effective than a control product in reducing dryness, and equally effective as a similar established product with a different humectant system. Other research has shown similar beneficial results with the topical use of NaPCA.13

Conclusion
NaPCA/PCA is the most prevalent natural moisturizing factor in human skin. It promotes SC water binding capacity, allowing the SC to maintain liquid water against the drying action of the environment. NaPCA/PCA levels can decline with age, skin conditions like psoriasis, and even with washing with soap. Topical use of cosmetic products containing NaPCA hydrates the skin and has been demonstrated to reduce skin dryness.

References:

  1. Harding CR, Rawlings AV. 18. Effects of Natural Moisturizing Factor and Lactic Acid Isomers on Skin Function. In Loden M, Maibach HI. Dry Skin and Moisturizers: Chemistry and Function, 2nd Edition. CRC Press; 2005:187–209.
  2. Schwartz J, Friedman AJ. Exogenous Factors in Skin Barrier Repair. J Drugs Dermatol. 2016 Nov 1;15(11):1289 – 94.
  3. Ibid.
  4. Fowler J. Understanding the Role of Natural Moisturizing Factor in Skin Hydration. Pract Dermatol. 2012;July:36 – 40.
  5. Laden K. Natural moisturization factors in skin. Am Perfum Cosmet. 1967; 82: 77–9.
  6. Harding CR, Rawlings AV. 18. Effects of Natural Moisturizing Factor and Lactic Acid Isomers on Skin Function. In Loden M, Maibach HI. Dry Skin and Moisturizers: Chemistry and Function, 2nd Edition. CRC Press; 2005:187–209.
  7. Ibid.
  8. Tucker R. What evidence is there for moisturizers? Pharm J Online. 2011;1:1– 4.
  9. Fowler J. Understanding the Role of Natural Moisturizing Factor in Skin Hydration. Pract Dermatol. 2012;July:36 – 40.
  10. Sodium PCA. The Derm Review. Retrieved April 22, 2019 from https://thedermreview.com/sodium-pca/
  11. Clar EJ, Fourtanier A. Pyrrolidone carboxylic acid and the skin. Int J Cosmet Sci. 1981 Jun;3(3):101–13.
  12. Middleton JD, Roberts ME. Effect of a skin cream containing the sodium salt of pyrollidone carboxylic acid on dry and flaky skin. J Cosmet Sci. 1978;29(4):201–205.
  13. Middleton JD, Roberts ME. Efficacy of a Skin Cream Containing Pyrrolidone Carboxylic Acid in Reducing the Incidence of Subclinical Dry Skin. In: Marks R, Dykes PJ (eds). The Ichthyoses. Springer, Dordrecht; 1978:177 – 80.

Gene Bruno, MS, MHS

Gene Bruno is the Dean of Academics and Professor of Dietary Supplement Science for Huntington College of Health Sciences (a nationally accredited distance learning college offering diplomas and degrees in nutrition and other health science related subjects. Gene has two undergraduate Diplomas in Nutrition, a Bachelor’s in Nutrition, a Master’s in Nutrition, a Graduate Diploma in Herbal Medicine, and a Master’s in Herbal Medicine. As a 32 year veteran of the Dietary Supplement industry, Gene has educated and trained natural product retailers and health care professionals, has researched and formulated natural products for dozens of dietary supplement companies, and has written articles on nutrition, herbal medicine, nutraceuticals and integrative health issues for trade, consumer magazines, and peer-reviewed publications. Gene's latest book, A Guide to Complimentary Treatments for Diabetes, is available on Amazon.com, and other fine retailers.

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