Pyrrolidone carboxylic acid (PCA), the primary constituent of the natural moisturizing factor (NMF),1 including its derivatives – such as simple2 and novel3 esters as well as sugar complexes4 – is the subject of great interest and research regarding its capacity to moisturize the stratum corneum via topical application.
Dr. Leslie S. Baumann
Creams and lotions containing the sodium salt of PCA are widely reported to aid in hydrating the skin and ameliorating dry flaky skin conditions.5,6 In addition, the zinc salt of L-pyrrolidone carboxylate is a longtime cosmetic ingredient due to antimicrobial and astringent qualities. This column briefly addresses the role of PCA in skin health.7
Dry skin
In a comprehensive literature review from 1981, Clar and Fourtanier reported conclusive evidence that PCA acts as a hydrating agent and that all the cosmetic formulations with a minimum of 2% PCA and PCA salt that they tested in their own 8-year study enhanced dry skin in short- and long-term conditions given suitable vehicles (no aqueous solutions).6
In a 2014 clinical study of 64 healthy white women with either normal or cosmetic dry skin, Feng et al. noted that tape stripped samples of stratum corneum revealed significantly lower ratios of free amino acids to protein and PCA to protein. This was associated with decreased hydration levels compared with normal skin. The investigators concluded that lower NMF levels across the depth of the stratum corneum and reduced cohesivity characterize cosmetic dry skin and that these clinical endpoints merit attention in evaluating the usefulness of treatments for dry skin.8
In 2016, Wei et al. reported on their assessment of the barrier function, hydration, and dryness of the lower leg skin of 25 female patients during the winter and then in the subsequent summer. They found that PCA levels were significantly greater during the summer, as were keratins. Hydration was also higher during the summer, while transepidermal water loss and visual dryness grades were substantially lower.9
Atopic dermatitis
A 2014 clinical study by Brandt et al. in patients with skin prone to developing atopic dermatitis (AD) revealed that a body wash composed of the filaggrin metabolites arginine and PCA was well tolerated and diminished pruritus. Patients reported liking the product and suggested that it improved their quality of life.10
Later that year, Jung et al. characterized the relationship of PCA levels, and other factors, with the clinical severity of AD. Specifically, in a study of 73 subjects (21 with mild AD, 21 with moderate to severe AD, 13 with X-linked ichthyosis as a negative control for filaggrin gene mutation, and 18 healthy controls), the investigators assessed transepidermal water loss, stratum corneum hydration, and skin surface pH. They found that PCA levels and caspase-14 were lower in inflammatory lesions compared with nonlesional skin in subjects with AD. These levels also were associated with clinical AD severity as measured by eczema area and severity index scores as well as skin barrier function.11