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A complete guide to polyglutamic acid (PGA) in skincare — the fermented amino acid polymer from Bacillus subtilis natto fermentation, why PGA holds 5000× its weight in water vs hyaluronic acid's 1000×, how PGA inhibits hyaluronidase (the enzyme that degrades HA), the film-forming mechanism that delivers longer-lasting hydration than HA alone, evidence for improved skin elasticity and moisture retention, and how to layer PGA with hyaluronic acid for synergistic maximum hydration.
· By MedSpot Editorial · 4 min read
Polyglutamic acid (PGA) is a naturally fermented polymer — the humectant that has been quietly outperforming hyaluronic acid in direct hydration comparisons while also protecting the HA that your skin already has. Here is the complete evidence-based guide.
Polyglutamic acid is produced by Bacillus subtilis bacteria during the fermentation of soybeans into natto — a traditional Japanese food. The sticky, stringy texture of natto is largely due to PGA.
In skincare, PGA is produced through controlled Bacillus fermentation — the bacteria secrete PGA as a natural polymer. It is:
| Humectant | Water-Holding Capacity | Primary Mechanism |
|---|---|---|
| Hyaluronic acid | ~1000× its weight | Hygroscopic — attracts and binds water |
| Polyglutamic acid | ~5000× its weight | Film-forming + hygroscopic |
| Glycerin | ~3× its weight | Hygroscopic |
| Beta-glucan | ~200× its weight (film) | Film-forming moisture lock |
PGA holds approximately 5× more water than HA per unit weight — the most hygroscopic cosmetic ingredient in common use.
Why such high capacity: PGA's polypeptide backbone has multiple carboxylic acid (–COOH) and amine groups along the glutamic acid chain — each capable of forming hydrogen bonds with water molecules. The three-dimensional coiled polymer structure traps and holds water in a structured network.
PGA forms a bioadhesive film on the skin surface — a thin polymer layer that:
The practical difference: HA provides faster initial hydration (rapid water uptake) that can dissipate faster, particularly in low-humidity environments (HA can draw moisture out of deep skin layers in very dry conditions). PGA's film retains moisture longer and is less environmentally dependent.
Hyaluronidase is an enzyme naturally present in skin that degrades hyaluronic acid — both the HA applied topically and the HA the skin produces endogenously. UV exposure, inflammation, and normal tissue turnover all increase hyaluronidase activity.
Polyglutamic acid competitively inhibits hyaluronidase — binding to the enzyme's active site and preventing it from degrading HA. This produces:
The clinical implication: Using PGA with HA is not merely additive — PGA amplifies HA's effect by protecting it from degradation while simultaneously providing its own superior water-holding capacity.
Narda M, Granger C, Trullas C. (2021). Polyglutamic acid in skincare. (and multiple manufacturer-independent published comparisons):
Split-face controlled studies applying PGA vs. HA to opposite cheeks demonstrate:
Elasticity improvement: Studies applying PGA at 1–2% for 4–8 weeks show significantly improved skin elasticity (cutometer measurements) vs. control — likely through combined direct mechanical film effect and HA protection enabling sustained HA-mediated extracellular matrix support.
High molecular weight PGA (HMW-PGA, > 1 MDa):
Low molecular weight PGA (LMW-PGA, 50–500 kDa):
Products often combine HMW and LMW PGA to achieve both surface film-forming and deeper epidermal hydration — the same strategy used with mixed-weight HA.
Optimal sequence:
PGA applied over HA (rather than under it) maximizes the HA-protective hyaluronidase inhibition effect and overlays the film-forming moisture lock on top of the hydrated surface.
Alternatively: Some formulations combine PGA + HA in a single serum — these typically show synergistic hydration superior to either alone.
PGA at higher concentrations can feel slightly tacky — the glutamic acid polymer has a distinctive film-forming texture. At 0.5–1%, this is minimal; at higher concentrations it may feel sticky on application. Many formulations use 0.5–1% for this reason.
PGA is compatible with all skincare actives — retinoids, vitamin C, AHAs, niacinamide, ceramides. No documented interactions. Suitable for all skin types including sensitive and acne-prone.
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