Polyglutamic acid, listed as Polyglutamic Acid or Sodium Polyglutamate, is a polymer made up of many glutamic acid units linked together. It is not extracted from a plant: it is obtained through bacterial fermentation, the same process behind natto, the Japanese food made from fermented soybeans from which the molecule was isolated.
It is a humectant that works on the surface and forms a film. It does one thing, does it well, and is not a replacement for anything.
Article written by Elisa Avalle, founder of LeLang Skin Care and dermocosmetics specialist. Cover image generated with the support of artificial intelligence.
How it works
It belongs to the same functional category as glycerin and hyaluronic acid: they are humectants, molecules that attract and retain water. What makes polyglutamic acid distinctive is its ability to bind a very large amount of water relative to its own weight and its tendency to form a thin film on the skin's surface.
That film has two practical effects. It slows the evaporation of the water it attracts, so surface hydration lasts longer, and it creates an immediate effect of smoother, slightly tighter-looking skin, which is why it is used in serums designed to deliver quickly visible results. Its high molecular weight keeps it on the surface: it is not an active ingredient that penetrates deeply, nor does it claim to do so.
What the data says, without the hype
The evidence for surface hydration and film formation is consistent. There is also a more ambitious claim: that polyglutamic acid inhibits the enzyme that breaks down hyaluronic acid, thereby preserving the hyaluronic acid produced by the skin. This is a hypothesis supported by some in vitro data, not an effect demonstrated in humans through cosmetic use. It should be presented for what it is.
There is also the question of quantity. It is an expensive raw material, and in many products it appears near the bottom of the INCI list, at percentages where its actual contribution is minimal while its name on the label does all the communication work. Its position in the list is the first thing to check.
Polyglutamic acid or hyaluronic acid?
The question is poorly framed because they are not competitors. Hyaluronic acid exists in different molecular weights, allowing it to work at multiple levels, with clinical literature that no other molecule in this family can match. Polyglutamic acid adds a more pronounced surface film and longer-lasting hydration in the short term.
In our formulas, hydration comes from hyaluronic acid with different molecular weights, which is the approach supported by the strongest experimental evidence. A serum containing both molecules is not a mistake: it is simply a product that works on two levels, not one that is worth twice as much.
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How to use it
- Apply to slightly damp skin, never completely dry skin: a humectant needs water to retain, otherwise it draws it from the deeper layers.
- Apply before creams, which seal in what the humectant has brought to the skin.
- In very dry environments, without an occlusive product on top, the benefit is greatly reduced. This applies to all humectants, including hyaluronic acid.
- It can be combined without problems with acids, retinoids, niacinamide, and vitamin C: there are no known incompatibilities.
Frequently asked questions
Is it suitable for oily skin?
Yes, and this is one of its strengths: it hydrates without adding lipids, so it is also suitable where a rich cream would feel heavy.
Can it cause reactions?
It is considered well tolerated. As always, reactivity is more related to the complete formula than to the individual ingredient.
Is it worth the price?
If it is present in a significant amount and the product is well formulated, it is a good humectant. If it is near the bottom of the list in a serum sold on the strength of its name, no.
Sources for this article
- Production of polyglutamic acid through bacterial fermentation and characterization of the polymer.
- Studies on the hygroscopic capacity and film formation of high-molecular-weight humectant polymers.
- In vitro data on the inhibition of the enzyme hyaluronidase and the limitations of extrapolating these findings to topical cosmetic use.
- Literature on humectants and occlusives and on the behavior of humectants in conditions of low ambient humidity.
Polyglutamic acid is a good ingredient that is often described in exaggerated terms. It hydrates the surface and keeps it smooth for longer: if that is what you are looking for, it works. If you are looking for a structural effect, that comes from other molecules and takes much more time.
