What Is Polyglutamic Acid (PGA)? Comparison with Hyaluronic Acid

Polyglutamic acid is the main component of the stringy structure in the Japanese food natto. The molecule forms when glutamic acid units build a long chain through an unusual bond (gamma bond), and it is produced by bacteria for cosmetic use. The salt form also appears on labels as Sodium Polyglutamate. Briefly called PGA, the same name covers chains of very different sizes: publications mostly mention the range of 100-1.000 kilodaltons (kDa), and in one new bacterial strain about 7.000 kDa was measured.

How reliable is the thousands-fold water claim?

Product promotions often say "holds 5.000 times its weight in water", but no measurement showing this exists in a peer-reviewed human skin study. The similar "thousand-fold" claim, and why it is controversial for hyaluronic acid, is also explained on the related page. Drawing water up in a closed container and holding moisture on the skin surface are not the same thing.

One of the few published laboratory comparisons was carried out in 2024. In a closed chamber at 70 °C, the water absorption of powder samples was measured. Hyaluronic acid led the commercial PGA samples for four hours; by the fourth hour, the difference with glycerin shrank for a commercial PGA of 10 kDa. Two special PGA samples produced from seaweed did surpass hyaluronic acid. This is a bench test, not a measurement on skin, but it shows that the distinction depends on source and size.

How much data is there on what it does in the skin?

In cell experiments and a reconstructed skin model, 1% PGA increased markers related to moisture and the barrier, such as filaggrin and aquaporin-3, as well as hyaluronic acid production. However, the authors of this study themselves say there is no human data, and some are company employees. As a humectant, supporting the feeling of moisture on dry skin is a reasonable expectation. Claims about spots, wrinkles or firming should be backed by evidence.

Who should use PGA with caution?

There is an important and little-known detail: in cases of severe allergic reaction (anaphylaxis) developing hours after eating natto, PGA has been shown to be the culprit. In one case, sensitisation is suggested to have started through the skin via a jellyfish sting. The authors reporting these cases advised patients to also avoid other products containing PGA. No case report of PGA allergy from cosmetics has been found, so this does not mean the product is risky. But if you have a natto allergy or a history of delayed-onset anaphylaxis, do not use these products without consulting your doctor.

For everyone else the standard method is sufficient: test on the inner arm or elbow crease for 7-10 days, twice a day. There is no separate record for PGA in the EU cosmetics regulation's restricted substances annexes. Applying a moisturiser on top instead of leaving it alone in dry air is a reasonable example of use.