Sodium PCA

Sodium PCA is a humectant: an ingredient that attracts and holds water. Its free acid, pyrrolidone carboxylic acid (PCA), is one of the main water-binding molecules skin makes for itself, which is why the salt is used in hydrating formulas.

At a glance

• Evidence level A. Published research on the ingredient itself.
• What it is. The sodium salt of PCA, a small molecule present naturally in the outer layer of skin.
• What it does. Binds water. Skin feels more hydrated and more comfortable.
• Caution. Very well tolerated in the literature. As with any product, patch test if your skin is reactive.

What it is

The outermost layer of skin, the stratum corneum, holds water with a mixture of small molecules known as natural moisturizing factor, or NMF. NMF forms inside surface skin cells as a structural protein called filaggrin breaks down. PCA is one of its main components, alongside free amino acids, lactate, urea and salts.

Sodium PCA is the sodium salt of that acid. Cosmetic grades are made from glutamic acid, an amino acid. It dissolves readily in water and draws moisture from its surroundings.

What it does in skincare

A humectant works by holding water in the upper layers of skin. Sodium PCA is used for that job in serums, toners, creams and hair products, usually alongside other humectants such as glycerin, lactic acid or betaine, because each binds water a little differently.

On its own, a humectant draws water; emollients and occlusives seal it in. That is why hydrating routines follow a humectant serum with a moisturizer containing emollients or occlusive ingredients, particularly in dry air. More on building a routine for this: hydration and barrier.

Evidence

The studies below describe the ingredient itself.

The case for PCA rests on what is known about skin's own moisturizing system. Scott and Harding showed in 1986 that filaggrin breaks down into water-binding compounds as the outer skin layer forms, and that the process responds to the humidity of the environment. Harding and colleagues later reviewed how natural moisturizing factor, including PCA, governs skin hydration and the shedding of surface cells.

Rawlings and Harding reviewed moisturization and skin barrier function in 2004, including the role of NMF components and why topical humectants are used. Verdier-Sévrain and Bonté reviewed the molecular mechanisms of skin hydration in 2007.

Most of this is mechanism: it explains why a PCA salt is a sensible humectant.

Use and caution

• Sodium PCA is widely used and rarely associated with irritation in the literature.
• Apply humectant serums to skin that is still slightly damp, then follow with a moisturizer.
• In very dry air, a humectant without an occlusive layer above it can leave skin feeling tight. Layer accordingly.
• As with any new product, patch test first if your skin is reactive.

In Vegalab products

The Hydrating NanoSerum sealed vial set lists sodium PCA as its fourth ingredient. It sits in a group of water-binding ingredients in that formula, with glycereth-26, butylene glycol, betaine, trehalose and ectoin.

• Hydrating NanoSerum, Sealed Vial Set

How to find an ingredient's place in a list: how to read an ingredient list.

Related ingredients

• Betaine, an osmolyte humectant
• Trehalose, a water-holding sugar
• Ectoin, an extremolyte
• Natural moisturizing factor
• All entries: ingredient library

References

1. Scott IR, Harding CR. Filaggrin breakdown to water binding compounds during development of the rat stratum corneum is controlled by the water activity of the environment. Dev Biol. 1986;115(1):84-92.
2. Harding CR, Watkinson A, Rawlings AV, Scott IR. Dry skin, moisturization and corneodesmolysis. Int J Cosmet Sci. 2000;22(1):21-52.
3. Rawlings AV, Harding CR. Moisturization and skin barrier function. Dermatol Ther. 2004;17(Suppl 1):43-48.
4. Verdier-Sévrain S, Bonté F. Skin hydration: a review on its molecular mechanisms. J Cosmet Dermatol. 2007;6(2):75-82.