What is it?
The sodium salt of PCA (pyrrolidone carboxylic acid, also called pyroglutamic acid), which forms from the amino acid glutamic acid. PCA occurs naturally in vegetables, fruits and molasses and in human skin, where it is part of the natural moisturizing factor that keeps the outer layer hydrated. In cosmetics, sodium PCA is a humectant that increases the water content of the skin’s top layers. It is used in moisturizers, eye creams, cleansers and hair products.
Key information
- Sodium PCA is a humectant based on PCA, a natural part of the skin's own moisturizing factor.
- The CIR Expert Panel concluded that PCA and its salts are safe in the present practices of use and concentration, a finding it updated in a 2015 amended report.
- It was reported in 1,289 products, at up to 2.5 percent in leave-on and 3 percent in rinse-off products.
- The panel said PCA and its salts should not be used in products in which N-nitroso compounds can form.
More information
PCA is made by heating L-glutamic acid with water under pressure, and sodium PCA is produced from sodium glutamate. In the skin, the natural moisturizing factor is a mix of free amino acids and their derivatives, including PCA, along with lactic acid, urea and salts. It makes up 20 to 30 percent of the dry weight of the stratum corneum. Levels decline with age, and routine soap washing removes it from the surface layers. The Cosmetic Ingredient Review (CIR) notes that PCA and sodium lactate are the most water-attracting part of that layer.
The CIR Expert Panel first assessed PCA and sodium PCA in 1999 and reviewed them again, adding three more salts, in an amended report released in 2015. It concluded that they are safe in the present practices of use and concentration. Sodium PCA was reported in 1,289 products, at up to 2.5 percent in leave-on products and 3 percent in rinse-off cleansers. Human patch tests at up to 32 percent caused no significant irritation, allergy or light-triggered reactions, although in one open test a few volunteers had redness on the back at 6.25 percent and above that faded within 30 minutes. It was not genotoxic in laboratory tests and caused no reproductive or developmental effects in rats.
The panel’s one condition is that PCA and its salts should not be used in products where N-nitroso compounds can form. These compounds, which include nitrosamines, can form when some nitrogen-containing ingredients react with nitrosating agents. In a laboratory test simulating stomach conditions, PCA reacted with nitrite very slowly, far more slowly than the comparison compounds. On labels, look for sodium PCA; PCA and its calcium, magnesium and potassium salts were covered by the same conclusion.
Sources: Cosmetic Ingredient Review: Safety assessment of PCA (2-pyrrolidone-5-carboxylic acid) and its salts as used in cosmetics, final amended report (2015); Practical Dermatology: Understanding the role of natural moisturizing factor in skin hydration
