What is Polyglutamic Acid?

Think of polyglutamic acid as a long chain of beads. Each bead is a unit of glutamic acid, an amino acid your body already makes and uses every day. String thousands of those beads together and you get a peptide: a big, water-loving molecule that is very good at holding on to moisture. "Poly" simply means "many", so polyglutamic acid literally means "many glutamic acids" linked together.

Made by fermentation (with a little help from natto)

PGA is made by fermentation, using a friendly bacterium called Bacillus subtilis. The same bacterium is behind natto, a traditional Japanese food made from fermented soybeans. That famously sticky, stringy texture you see when you lift natto with chopsticks? That's largely polyglutamic acid. Yes, really. A 2025 review of microbial poly-glutamic acid in the journal Fermentation explains how this process works and why PGA's structure makes it so good at binding water.

For skincare, fermentation is a useful route. It produces a consistent, vegan-friendly ingredient without relying on animal sources, and the result is a clear, silky material that works well in light serums.

Why size matters for where it works

PGA is a very large molecule. Smaller humectants can settle into the upper layers of the skin, but PGA is too big to do that, so it stays on the skin's surface. That is exactly its strength: it holds moisture right where you feel it, which is why skin feels instantly smoother and more cushioned after you apply it.

Why "acid" doesn't mean exfoliation

When most of us hear "acid" in skincare, we think of glycolic or salicylic acid, ingredients that loosen dead skin cells and can tingle on application. Polyglutamic acid is not in that family.

In PGA's case, "acid" describes its chemical structure, not what it does to your skin. Our serum sits at a near-neutral pH of 6.0-7.0, nowhere near the low pH exfoliating acids need to work. It won't resurface, peel or sensitise skin the way an exfoliant can. Our guide to skincare acids explains why not every acid exfoliates.

Humectant vs film-former, explained simply

A humectant attracts water. Picture a sponge: it pulls moisture towards itself and holds it. Hyaluronic acid and glycerin are classic humectants.

A film-former lays a thin, breathable, flexible layer over the skin. Picture a lid on a pan: it doesn't add more water, but it helps slow down how quickly the water escapes.

PGA does a bit of both.

Humectant = draws water in. Film-former = helps keep it there.

That's why PGA is often described as a "moisture lock". It isn't heavy or greasy like a traditional balm, yet it still helps slow down water loss in a way that a pure humectant alone can't.

→ What is a humectant?
→ Hyaluronic Acid Ingredient Guide

Holds moisture at the surface and helps slow water loss

PGA's film-forming action helps keep skin feeling hydrated for longer, so that tight, thirsty feeling doesn't creep back by mid-afternoon. Lab studies suggest PGA can support moisture retention. One 2025 study using a reconstructed skin model, published in IJMS, looked at how poly-γ-glutamic acid helps hold water. This is lab research rather than a promise of personal results, but it backs up what many people notice day to day.

Instantly smooths the look of fine lines and texture

Because PGA holds water at the surface, it instantly softens the look of fine lines and rough-feeling texture. This is a surface smoothing effect. Research into the film-forming properties of PGA fractions helps explain how that smooth, flexible layer forms.

Works as a primer and makeup prep

That same smooth film gives foundation a softer base to sit on, so it clings less to dry patches. For more ideas, see our guide to prepping skin before makeup.

Helps your other hydrators work harder

Applied after hyaluronic acid, PGA helps keep that freshly drawn-in hydration in place instead of letting it evaporate.

"Hyaluronic Acid draws moisture in, Polyglutamic seals it in."

Suits nearly everyone, including sensitive skin

PGA is fragrance-free, has a near-neutral pH and sits on the surface of the skin, which makes it a gentle option for almost every skin type. As with anything new, patch test first.

Sounds good, but does your skin actually need it? Here's how to tell.

Honest answer: not everyone does. First, a quick distinction. Dehydrated skin lacks water. Dry skin lacks oil. Any skin type, including oily skin, can be dehydrated, and PGA is especially helpful for dehydration.

Signs polyglutamic acid could help

• ✓ Your skin feels hydrated after your routine, but that feeling has faded by lunchtime
• ✓ Your skin feels tight in central heating, air-conditioned offices or cold weather
• ✓ Your makeup clings to dry patches or looks patchy by the afternoon
• ✓ Your skin's texture looks dull, rough or uneven, even though you moisturise
• ✓ You use hyaluronic acid but the effect doesn't last

When you might not need it

If your skin feels comfortable all day with a hyaluronic acid serum and a good moisturiser, you may not need PGA at all. It's optional, not essential. It earns its place when hydration isn't lasting, when the weather turns, or when you want a smoother base for makeup.

Our skin flooding guide explains how to layer hydrators for maximum comfort, and humectants vs occlusives explains why these two ingredient types work so well together. If dehydration is your main concern, shop for dehydrated skin.

1. Cleanse, then apply Hyaluronic Acid Serum to damp skin.
2. Apply any treatment serum, e.g. retinol at night or vitamin C in the morning.
3. Apply a pea-sized amount of Polyglutamic Acid Serum as your last serum. Pat it into your face and neck.
4. Always seal with moisturiser.
5. Use AM and PM. Finish with SPF in the morning.

Cleanse → Hyaluronic Acid Serum (damp skin) → Treatment → Polyglutamic Acid Serum → Moisturiser → SPF (AM)

Layer from thinnest to thickest texture, and patch test any new product first.

A pea-sized amount covers your whole face and neck. Using too much is the number one reason people see pilling.

To be open about why it happens: our serum contains silicones, with dimethicone high on the ingredient list. They give it its silky, smoothing feel, but too much product, or stacking it with other silicone-heavy products, can make layers roll up.

How to stop polyglutamic acid pilling

• Use a pea-sized amount, no more
• Wait 30-60 seconds before moisturiser
• Avoid heavy, silicone-rich moisturisers or primers on top
• Pat it in, don't rub

If you're already using hyaluronic acid or glycerin, you might be wondering where PGA fits. Here's how they compare.

Not alternatives, a team. Hyaluronic acid and glycerin draw water in. PGA helps hold it at the surface. Ceramides support the barrier that keeps everything in balance. If you only choose one hydrating serum, hyaluronic acid is a great everyday starting point. Add PGA when you want that hydration to last longer.

→ Polyglutamic Acid vs Hyaluronic Acid
→ Glycerin Ingredient Guide
→ Ceramides Ingredient Guide

Yes. PGA can be used with AHAs, BHAs and retinol, morning and evening.

Retinol: yes. Helps keep skin comfortable while it adjusts. Apply Retinol Serum, then PGA, then moisturiser. → Retinol guide
Vitamin C: yes. In the morning, apply 15% Vitamin C + EGF Serum first, then PGA, moisturiser and SPF. → Vitamin C guide
Niacinamide: yes. A great pairing for oily or combination skin. → Niacinamide guide
Exfoliating acids (AHA/BHA): yes. Use PGA afterwards to replace hydration, e.g. after Glycolic Acid Toner or Beta Hydroxy Acid (BHA) Serum.
Ectoin: yes. Ectoin Hydro-Barrier Serum supports the barrier, and PGA helps hold the moisture in.
Prescription products: check with your doctor before adding new products.

Yes. Oily skin can still lack water, which can leave it looking dull or feeling tight even while it shines. PGA is lightweight with an oil-free feel. Seal it with Omega Water Cream for a light finish, and add Niacinamide Serum before PGA if shine is your main concern.

Blemish-prone skin needs hydration too, but it often needs it to feel light. PGA hydrates without a heavy, rich texture, which is why many people who get breakouts like it. Everyone's skin is different, so patch test first.

Where PGA really helps is alongside clearing ingredients, which can sometimes leave skin feeling tight. Try it with 360 Skin Clearing Serum or Salicylic Acid Cleanser, then follow with a light moisturiser.

PGA is fragrance-free, near-neutral and works on the surface, so it's a gentle choice. Patch test before applying it all over. If your barrier feels compromised, start with our damaged skin barrier guide.

"Why can I smell it if it's fragrance-free?" Fragrance-free means no added fragrance. Some ingredients have their own natural scent, and a few customers notice a faint smell on application. It fades once the serum settles.

PGA is generally considered suitable during pregnancy, and our Polyglutamic Acid Serum is labelled as suitable for pregnancy and breastfeeding. Every pregnancy is different, so always check your skincare routine with your doctor or midwife, especially if you use other active ingredients.

Polyglutamic Acid Serum, £15 | 30ml

Lock in moisture for smooth skin instantly.

• 3% Polyglutamic Acid Complex: locks in moisture and softens the look of surface lines
• 2% Invisaskin: supports long-lasting hydration and smoother-looking skin
• Silky, fast-absorbing texture | pH 6.0-7.0 | Results in up to 6 weeks with consistent use
• Fragrance-free, vegan (certified by The Vegan Society), Leaping Bunny approved, gluten-free, 100% recyclable packaging
• How to use: a pea-sized amount after your hydrator, then moisturiser, then SPF in the morning
• Customer tips: use it as a primer, mix a drop into foundation for a dewy finish, or wear it under makeup all through party season

Customers often say it leaves skin feeling "soft, silky" and works beautifully under makeup.

Shop Polyglutamic Acid Serum

Pair it with

• Hyaluronic Acid Serum, £12. Apply first on damp skin to draw water in, then let PGA help hold it there.
• Ectoin Hydro-Barrier Serum, £16. Supports a stressed, weather-worn barrier.

Seal it in

• Omega Water Cream. A light gel-cream for oily or combination skin.
• Bio-Active Ceramide Moisturiser. A richer option for dry skin or early signs of ageing.

Polyglutamic acid helps hold moisture at the skin's surface, so skin feels smoother and more comfortable for longer. Despite its name, it isn't an exfoliant. It works best after hyaluronic acid and before moisturiser, and it suits almost every skin type. You don't need more skincare. Just the right layer in the right place.

Shop Polyglutamic Acid Serum

Not sure where to start? Take the INKEY Skincare Quiz | Build your routine

• Hyaluronic Acid
• Glycerin
• Ceramides
• Damaged Skin Barrier
• Niacinamide
• Retinol
• What's Your Skin Type?
• Skincare Routine Guide