Pyrrolidone carboxylic acid (PCA) in Skincare — Your Skin's Own Hydrator
Quick Answer
PCA is a humectant that is part of your skin's own Natural Moisturising Factor. True — and it leaves out where NMF comes from, which is the interesting part.
NMF is not a blend your skin assembles. It is produced by breaking down a protein called filaggrin into amino acids — and one of those, glutamine, is converted into PCA. PCA is a filaggrin breakdown product.
That matters because filaggrin mutations are the strongest known genetic risk factor for eczema, and people who carry them have measurably less NMF — including less PCA. So there is a real reason PCA suits very dry skin, beyond it simply being gentle. On labels, look for "sodium PCA".
Most hydrating ingredients are borrowed from elsewhere. PCA is a molecule your skin manufactures itself — and understanding how it does that explains far more than the usual description.
What we'll cover
Where PCA Actually Comes From
Natural Moisturising Factor is usually described as a mixture of water-binding substances sitting in the outer skin. Accurate, and it makes NMF sound like something the skin stocks. It is closer to something the skin manufactures on demand, from a specific raw material.
From protein to humectant
As skin cells move toward the surface and flatten, a protein called filaggrin does a structural job — helping bundle keratin filaments together. Once that job is done, filaggrin is broken down into its constituent free amino acids.
Those amino acids are then converted into the water-binding molecules that make up NMF. Glutamine becomes PCA. Histidine becomes urocanic acid. Others remain as free amino acids.
So PCA is a filaggrin breakdown product — the second career of a structural protein, repurposed into a humectant once its scaffolding work is finished. Which is a rather elegant piece of biology, and it explains why NMF levels track with how well that process is working.
This reframes what topical PCA is doing. It is not adding a foreign humectant that happens to be well tolerated — it is supplying the end product of a pathway that may be underperforming, which is a more specific rationale than "skin recognises it."
The Filaggrin And Eczema Connection
Here is why the filaggrin detail is more than trivia.
The strongest known genetic risk factor
Loss-of-function mutations in the filaggrin gene are the strongest identified genetic risk factor for atopic dermatitis — a finding that reshaped how eczema is understood, shifting emphasis toward barrier defects rather than immune dysfunction alone.
And because NMF is made from filaggrin, people carrying these mutations have measurably reduced NMF — including reduced PCA — in their stratum corneum. NMF levels can even be used to infer filaggrin status.
So the link between very dry, atopic-prone skin and low PCA is not a marketing association. It is the same molecule, downstream of the same gene.
Being clear about what this does and does not mean
This explains why hydrating ingredients matter for dry, atopic-prone skin. It does not mean a cosmetic product treats eczema — atopic dermatitis is a medical condition requiring proper assessment and management, and no humectant addresses the underlying genetics. Cosmetic hydration supports comfort alongside medical care; it does not substitute for it. If your skin is persistently itchy, inflamed or cracking, that is a doctor's question.
Your Skin Adjusts It To The Weather
A second detail follows from NMF being made rather than stored: the rate of filaggrin breakdown responds to external humidity. In drier air, more filaggrin is processed into NMF — the skin producing additional humectant precisely when the environment is pulling water away.
It is a genuinely elegant regulatory system, and it has a practical consequence. Skin can compensate to a degree, but the compensation has limits — and it depends on having enough filaggrin to work with. In prolonged air conditioning, or for someone whose filaggrin pathway is compromised, that headroom runs out.
The humectant catch, which applies to PCA too
Humectants draw water from their surroundings. In dry air there is little atmospheric water available, so more comes from deeper in your own epidermis — and if the layer is left unsealed, it evaporates and takes some of yours with it. Always follow a humectant layer with a moisturiser. This is not fussiness; it is the difference between the layer helping and doing nothing.
What To Look For On A Label
You will rarely see "PCA" alone. The cosmetic ingredient is almost always sodium PCA — the sodium salt, which is more stable and more water-soluble than the free acid. Occasionally you may see other salt forms such as zinc PCA, which is sometimes chosen in oily-skin formulations.
| On the label | What it is |
|---|---|
| Sodium PCA | The usual cosmetic form — stable, water-soluble, humectant |
| Zinc PCA | A different salt, sometimes used in oily or blemish-prone formulations |
| Pyrrolidone carboxylic acid | The free acid — the same molecule under its full chemical name |
A common confusion worth settling: the word "acid" here signals nothing about exfoliation. PCA is not an AHA, does not exfoliate, and does not increase sun sensitivity. It sits in formulations for the same reason glycerin does.
How To Use It Properly
- Apply to damp skin. Humectants need water available to bind. Bone-dry skin gives them less to work with and more reason to draw from your own tissue.
- Then seal, without exception. A moisturiser over the top is what keeps the water where you put it — and the drier the air, the more this matters.
- Layer with other humectants freely. PCA, glycerin, hyaluronic acid and panthenol bind water by broadly similar means and are complementary rather than competitive.
- Use it daily. There is no tolerance-building or cycling needed — it is not an active in that sense.
- Do not expect it to replace lipids. Water and lipids are different deficits. Genuinely dry skin needs a lipid-containing cream as well, not just more humectant.
A realistic note
PCA is a well-understood, well-tolerated humectant, and it is a supporting ingredient rather than a hero. It will not change the structure of your skin barrier or address why NMF is low in the first place. Persistently dry, itchy, cracking or inflamed skin warrants a proper assessment rather than a longer ingredient list.
Frequently Asked Questions
What is PCA and where does it come from?
It is a humectant and a component of your skin's Natural Moisturising Factor — and specifically, a breakdown product of a protein called filaggrin. Once filaggrin has finished its structural job in the outer skin, it is broken into free amino acids, and glutamine among them is converted into PCA. So your skin manufactures it from a protein it was already using for something else.
Why is PCA associated with very dry and eczema-prone skin?
Because of the same filaggrin link. Loss-of-function mutations in the filaggrin gene are the strongest known genetic risk factor for atopic dermatitis, and since NMF is made from filaggrin, carriers have measurably reduced NMF including reduced PCA. The connection is mechanistic rather than marketing. That said, cosmetic hydration supports comfort — it does not treat eczema, which needs medical management.
Is PCA an exfoliating acid?
No, despite the name. It does not exfoliate, does not affect skin pH meaningfully at use levels, and does not increase sun sensitivity. It belongs with glycerin and hyaluronic acid rather than with glycolic or salicylic acid — the "acid" in its chemical name describes its structure, not its behaviour on skin.
Why do labels say sodium PCA?
Because the sodium salt is the form normally used — it is more stable and more water-soluble than the free acid. You may occasionally see zinc PCA, a different salt sometimes chosen for oily or blemish-prone formulations. If you are scanning a label for this ingredient, "sodium PCA" is the phrase to look for.
How is it different from hyaluronic acid?
Both bind water, but PCA is a small molecule your skin makes itself as part of NMF, while hyaluronic acid is a much larger polymer better known for the volume of water it can hold. They are complementary rather than alternatives, and appear together in plenty of formulations. Neither replaces a lipid-containing moisturiser.
Does my skin make more of it in dry weather?
Yes, to a degree — the rate at which filaggrin is broken down into NMF increases at lower external humidity, so skin produces more humectant precisely when the air is pulling water away. It is a neat regulatory system with real limits, and prolonged air conditioning or a compromised filaggrin pathway can exceed them.
Can a humectant make my skin drier?
If left unsealed in dry air, potentially. Humectants draw water from their surroundings, and when little is available in the air they take more from deeper in your own epidermis — which then evaporates from an uncovered surface. Always follow a humectant layer with a moisturiser. This applies to PCA as much as to any other humectant.
The Bottom Line
PCA is not simply a gentle humectant that skin recognises — it is a filaggrin breakdown product, manufactured by your skin from a structural protein once that protein's first job is done. Since filaggrin mutations are the strongest genetic risk factor for eczema, the link between low PCA and very dry skin is mechanistic. Look for sodium PCA on labels, apply to damp skin, and always seal it.
References
- Rawlings AV, Harding CR. Moisturization and skin barrier function. Dermatologic Therapy. 2004;17(Suppl 1):43–48.
- Palmer CNA, Irvine AD, Terron-Kwiatkowski A, et al. Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis. Nature Genetics. 2006;38(4):441–446.
- Kezic S, Kemperman PMJH, Koster ES, et al. Loss-of-function mutations in the filaggrin gene lead to reduced level of natural moisturizing factor in the stratum corneum. Journal of Investigative Dermatology. 2008;128(8):2117–2119.
- 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. Developmental Biology. 1986;115(1):84–92.
- Boldpurity in-house data: protocol SKIN-BPAG-2025-01, in-vivo study, MS Clinical Research Bangalore, IEC-ACE approved, N=30 completers, 8 weeks, Fitzpatrick III–V.
Note to editor: the previous list contained two regulations plus Rawlings & Harding, which was correct but did not support the article's specific claims. These are the primary sources for the filaggrin pathway described. Please verify before publication.
Disclaimer
This article is for informational purposes only and is not medical advice. Descriptions of filaggrin, Natural Moisturising Factor, humidity regulation and genetic risk factors describe published research and general skin biology, not the effect of any product. Atopic dermatitis and eczema are medical conditions requiring assessment and management by a qualified clinician; no cosmetic product treats them, and filaggrin genetics are referenced here only to explain the biology of PCA. No claim is made that any Boldpurity product contains PCA. Humectants, moisturisers and cleansers are referred to as general product categories. Persistently dry, itchy, cracking or inflamed skin should be assessed by a qualified dermatologist rather than managed with cosmetic products alone. Aligned with the India CDSCO cosmetic framework, the Cosmetics Rules 2020 and the ASCI Code 2021. Results may vary. Patch test before use.
