Polyglutamic Acid, Explained: Why It Out-Binds Hyaluronic Acid in the Lab but Not on Your Skin

The headline number is real, and also not the whole story

What a formulated in-use study actually found

A published comparison of gamma-polyglutamate formulations measured water retention against both an untreated control and a reference hyaluronic acid formulation over 120 minutes. The PGA formulation held 45% retention, the HA reference formulation held 36%, and the untreated control sat at 40%. Notably, lower concentrations of PGA performed comparably to higher concentrations of glycerol in the same testing, meaning PGA doesn't need to be used at a high percentage to contribute measurable humectant effect -- which is one reason it shows up fairly low on ingredient lists and still gets marketed as a headline ingredient.

Where hyaluronic acid actually wins: staying power

The more practically important finding is about persistence, not peak capacity. Hyaluronic acid applied topically has been shown to persist in the upper epidermis for up to 72 hours. PGA, despite its larger theoretical water-binding number, is broken down much faster: skin studies found its half-life is under 8 hours, because epidermal peptidases -- enzymes naturally present in skin -- hydrolyze the polymer relatively quickly. In practice, that means a product built around PGA alone needs more frequent reapplication to sustain the same hydration than one built around HA, even though PGA's raw water-holding number looks more impressive on paper.

What PGA actually is

Polyglutamic acid is a biopolymer, most commonly produced by fermenting Bacillus subtilis -- the same bacterial family used to ferment soybeans into Japanese natto and Korean cheonggukjang. In skincare, it functions as a humectant: it forms a lightweight, flexible film on the skin's surface that helps hold moisture at the surface layer rather than penetrating deeply, similar in mechanism to how hyaluronic acid operates but with a different molecular structure and, per the persistence data above, a shorter functional window on skin.

Why it's usually paired with other humectants, not used alone

Because PGA's water-binding advantage shows up most clearly at the moment of application and fades faster than HA's, most formulations pair it with hyaluronic acid of multiple molecular weights, glycerin, or both, rather than relying on PGA as the sole humectant. This layering approach is consistent with the broader logic covered in this site's breakdown of humectants versus occlusives and emollients: a humectant only holds water it can access, so pairing a fast-acting, high-capacity ingredient like PGA with a longer-lasting one like HA, and finishing with an occlusive to reduce evaporation, tends to outperform any single humectant used in isolation.

Getting more out of it: application matters as much as the ingredient

Since PGA's water-binding only works on water that's actually present, applying a PGA serum to damp skin -- right after cleansing or misting, before the product fully dries down -- gives it more moisture to hold onto than applying it to already-dry skin. This is the same principle behind the skin flooding technique, and it applies to PGA arguably more than to HA, given how quickly PGA's effect can fade once there's no surface moisture left for it to bind.

Who tends to notice the difference

People with normal-to-dry skin often report PGA formulations feeling smoother and less tacky than comparable HA formulations, which tracks with PGA's distinct film-forming texture rather than any proven difference in long-term hydration outcomes. It is generally well tolerated, including on reactive or barrier-compromised skin, since it's a large, surface-acting molecule rather than an exfoliant or active ingredient with a irritation profile to manage. As with any new product, patch-test on a small area first, and see a dermatologist for diagnosis or treatment of any persistent skin concern -- this article explains general skincare chemistry and is not medical advice.