Polyglutamic acid guide: the next-generation humectant that outperforms hyaluronic acid

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.

What polyglutamic acid is

Origin: natto fermentation

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:
A polypeptide (chain of L-glutamic acid amino acid units)
Typically 500 kDa – 2 MDa (much larger than HA's 1–2.5 MDa in cosmetic use, though molecular weight varies significantly by production method)
Water-soluble; negatively charged at skin pH; forms a viscous film on skin

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Why PGA outperforms HA on surface hydration

Water-holding capacity comparison

| 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.

Film-forming mechanism

PGA forms a bioadhesive film on the skin surface — a thin polymer layer that:
Acts as a physical moisture barrier, reducing TEWL
Holds the water it has attracted within the film structure
Provides a longer moisture-retention duration than HA (which releases water more readily)

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.

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The HA-protecting mechanism: hyaluronidase inhibition

What hyaluronidase does

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.

PGA inhibits hyaluronidase

Polyglutamic acid competitively inhibits hyaluronidase — binding to the enzyme's active site and preventing it from degrading HA. This produces:
Extended duration of applied HA — HA layered under or over PGA degrades more slowly, maintaining hydration longer
Protection of endogenous skin HA — the dermal HA your fibroblasts produce is protected from accelerated enzymatic breakdown

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.

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Evidence

Skin moisture and elasticity

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:
Significantly higher skin capacitance (hydration measurement) on the PGA side at 2, 4, and 6 hours
Significantly greater TEWL reduction on the PGA side
Superior performance in low-humidity conditions (PGA less dependent on environmental moisture than HA)

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.

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Molecular weight considerations

High molecular weight PGA (HMW-PGA, > 1 MDa):
Superior film-forming on the skin surface
Better moisture retention
Limited skin penetration — works primarily at the stratum corneum surface

Low molecular weight PGA (LMW-PGA, 50–500 kDa):
Some penetration into the upper epidermis
More systemic humectant activity within the stratum corneum
Less surface film formation

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.

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How to use PGA

Layering strategy for maximum hydration

Optimal sequence:
Essence/serum with LMW HA — pulls water into deeper layers
PGA serum or layer — locks moisture at the surface with film; inhibits hyaluronidase to protect applied HA
Moisturizer with ceramides — seals both hydrating layers with barrier lipids

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.

Texture note

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.

Compatibility

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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