Sodium PCA is a naturally occuring humectant that functions as a hydrating agent and a skin-replenishing ingredient in a variety of skin and hair care products.
Sodium PCA is the salt form of pyrrolidone carboxylic acid, also known as pyroglutamic acid, which is the cyclic lactam of glutamic acid. PCA was first discovered by Haitinger in 1882, who found that when heated at 180°C, glutamate is converted into pyroglutamate by losing a molecule of water. PCA is present in nearly all living cells, from bacteria to humans, where it is derived from glutathione (an antioxidant) through the action of the enzyme γ-glutamyl cyclotransferase.
Additionally, PCA is created through the breakdown of the protein filaggrin within corneocytes. Corneocytes are dead skin cells that make up the stratum corneum, the outermost layer of skin that serves as a protective barrier. Within the stratum corneum, the amino acid-derived products of filaggrin breakdown (i.e. PCA) along with several small compounds including sugars and electrolytes, form natural moisturizing factor (NMF). Together with the naturally-occurring lipids in skin, NMF components work to keep skin’s surface intact, supple, and hydrated.
Sodium PCA 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%.
A humectant is a hygroscopic 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, sodium PCA helps keep the skin hydrated and may also help other topical skin care ingredients to perform better.
As mentioned above, PCA is a natural component of the skin’s NMF. Therefore, topically applied sodium PCA is able to mimic the NMF. Skin care expert Paula Begoun explains that restoring the skin’s NMF is important because it becomes depleted with age and also from routine exposure to sensitizing ingredients like drying cleansing agents and denatured alcohol. This leads to visibly dry, tight-feeling, flaky skin. Thus, by using ingredients that help to replenish NMF, signs of aging such as lines, wrinkles, and dry skin, will be reduced. The result is skin that appears more smooth, hydrated, and firm. Sodium PCA is non-comedogenic, which means it will not cause or worsen acne.
Sodium PCA is also used in hair care products. It is known to enhance the appearance and feel of hair, by increasing hair body, suppleness, or sheen, or by improving the texture of hair that has been damaged physically or by chemical treatment.
The safety of PCA and sodium PCA has been assessed by the Cosmetic Ingredient Review (CIR) Expert Panel. The CIR Expert Panel evaluated the scientific data and concluded that PCA and sodium PCA are safe for use in cosmetics and personal care products.
In animal studies, sodium PCA was non-irritating to the eye and skin at concentrations up to 50%. No evidence of phototoxicity, sensitization, or comedogenicity was found. These ingredients were not genotoxic. In a range of clinical tests, PCA and sodium PCA were found to be non-irritating and non-sensitizing (with and without UV exposure). Topically applied sodium PCA has low skin penetration, which is why reproductive and developmental toxicity data were not critical to completion of the safety assessment.
However, sodium PCA should not be used in cosmetic products containing nitrosating agents. This is because in the presence of certain chemicals and in heat and light, sodium PCA can break down and create carcinogenic nitrosamines.
According to EWG, sodium PCA is rated as a 1 on a scale of 1 to 10, with 1 being the lowest risk to health and 10 being the highest.
References: Wikipedia, “Pyroglutamic Acid”, Current Science, 102(2), 25 Jan 2012, J Clin Aesthet Dermatol. 2011 Jun; 4(6): 45–55, Paula’s Choice, “Natural Moisturizing Factor”, Cosmetics Info, “PCA and Sodium PCA”, Int J Toxicol. March 1999; 18(2) suppl 25-34, Chemical of the Day, “Sodium PCA”, 2011, EWG’s Skin Deep Cosmetic Database, “Sodium PCA”.