TL;DR
Polyglutamic acid (PGA) is a humectant made from the fermentation of Bacillus subtilis natto. It holds about four times its weight in water on the skin surface, slows water evaporation by forming a thin film, and slightly inhibits the enzyme that breaks down hyaluronic acid. Best used on damp skin, layered with hyaluronic acid, not as a replacement.
The dueling humectant headline is a setup. Polyglutamic acid is sold as a hyaluronic acid alternative, but the molecules behave differently enough that pitting them against each other misses the point. They work better together.
What polyglutamic acid actually is
Polyglutamic acid is a chain of glutamic acid units produced through the fermentation of Bacillus subtilis natto, the same bacterium responsible for the sticky Japanese natto bean dish. The molecule is a polypeptide, fully water-soluble, with a high molecular weight that keeps it on the surface of the skin rather than penetrating deep. Pre, pro, and postbiotics in skincare covers where it sits in the fermentation skincare family.
The water-holding numbers are misleading on purpose
This is the contrarian section. You will see polyglutamic acid sold as holding four times more water than hyaluronic acid. That figure compares PGA’s gravimetric water binding on the skin surface to a specific HA fraction. It is technically defensible and practically misleading. Hyaluronic acid works in part by penetrating the upper epidermis through its lower-weight fractions and pulling water into the skin matrix. Polyglutamic acid sits on the surface, forms a humectant film, and slows transepidermal water loss. Different mechanisms. Different layers. The 4x claim invites you to swap one for the other, when stacking them is the actual win. Polyglutamic acid vs hyaluronic acid, tested goes deeper into this comparison.
What the clinical work shows
A 2018 study in the Journal of Cosmetic Dermatology applied 0.1 percent polyglutamic acid serum to 27 volunteers twice daily for four weeks. Corneometer hydration readings improved 35 percent over baseline, and transepidermal water loss decreased 12 percent. Indexed work in PubMed supports the surface-humectant mechanism, particularly the inhibition of hyaluronidase, the enzyme that breaks down endogenous hyaluronic acid.
For broader context, hyaluronic acid molecular weight, misuse, and why it sometimes backfires walks through how molecular weight determines what a humectant actually does.
Where it fits in a routine
On damp skin, after cleansing, under heavier moisturizer. The film effect needs moisture underneath to lock in. Applied to bone-dry skin in dry air, polyglutamic acid can pull water from your skin rather than into it, the same caveat that applies to all surface humectants. Dry skin vs dehydrated skin covers when this matters most.
Who should use it
Dehydrated, sensitive, and dry skin types. Anyone who finds hyaluronic acid alone leaves their skin still feeling tight in dry climates or air conditioning. People in cities with low humidity, frequent flyers, and anyone using a strong retinoid who wants a comfort layer. Our Microbiome Glow Serum formulates polyglutamic acid at 0.2 percent alongside multi-weight hyaluronic acid for layered hydration. The dehydration tag has more on this. For a deeper read on how humectants stack, snow mushroom (tremella) covers a related plant alternative.
How to layer polyglutamic acid without overthinking
Damp skin first. PGA serum second. Hyaluronic acid serum third if used. Then ceramide or fatty alcohol moisturizer. The moisturizer step is non-negotiable. A humectant without an occlusive on top is half the equation.
What I’d skip
Cleansers and toners marketed around polyglutamic acid. The contact time is too short for any meaningful hydration effect. Save your PGA budget for a leave-on serum where the molecule actually has time to form a film.
FAQ
Is polyglutamic acid the same as glutamic acid? No. Polyglutamic acid is a long chain of glutamic acid units. Glutamic acid alone is a single amino acid with different properties.
Can I use it with hyaluronic acid? Yes, and stacking them is the most effective approach.
Is it pregnancy safe? Yes. No known concerns.
Will it cause breakouts? Rare. It is a surface humectant with low irritation potential.
How long until results? Surface hydration improves within hours. Sustained barrier comfort builds over two to four weeks.
Sources: Journal of Cosmetic Dermatology (2018); PubMed Central, Polymers Journal (2017); American Academy of Dermatology (2024).
Tool: pregnancy-safe skincare planner — ingredients to avoid + safer alternatives by trimester.
Tool: dehydrated-vs-dry-skin test — they look the same but need opposite products.
Keep reading
Tool: layering order tool — drag-and-drop your products, get the right sequence.