You apply your hyaluronic acid serum on damp skin. You lock it in with moisturizer. And by 2 p.m., your cheeks feel tight again. Sound familiar?
That’s not you doing it wrong. That’s hyaluronic acid doing what hyaluronic acid does—evaporating.
Polyglutamic acid (PGA) doesn’t have that problem. It’s a humectant that holds water differently. And if you’re tired of the hydration-then-dehydration cycle, this is the ingredient worth understanding.
What Polyglutamic Acid Actually Is (And Why It’s Not Just Another Trend)
Polyglutamic acid is a water-soluble peptide derived from fermented soybeans. Natto, specifically—the sticky, stringy Japanese breakfast food. The same fermentation process that makes natto slimy produces long chains of glutamic acid molecules. Those chains are what we call PGA.
In skincare, PGA functions as a humectant. It pulls water from the environment and from deeper skin layers toward the surface. But the mechanism differs from hyaluronic acid in two critical ways.
Molecular Weight: Why Size Matters More Than You Think
Hyaluronic acid is a large molecule. Even the “low molecular weight” versions sit around 50,000 Daltons. Most HA in serums ranges from 500,000 to 2 million Daltons. That’s big. Too big to penetrate past the stratum corneum in any meaningful amount.
PGA molecules are even larger—often exceeding 1 million Daltons. This sounds like a disadvantage, but it’s actually the feature. Because PGA sits entirely on the skin’s surface, it forms a hydrogel film. That film does two things: it holds water against the skin, and it physically slows transepidermal water loss. HA can’t form that same occlusive-like film.
The Inkey List’s Polyglutamic Acid Serum uses a 3% PGA concentration with this exact mechanism in mind. It’s not trying to penetrate. It’s building a water-trapping net on top of your skin.
Water-Binding Capacity: The 4x Claim Explained
You’ll see everywhere that PGA holds 4 times more water than hyaluronic acid. The actual number comes from in-vitro studies measuring water-binding capacity by weight. PGA binds roughly 4,000 to 5,000 times its weight in water. HA binds around 1,000 times.
But here’s what those numbers don’t tell you: binding capacity only matters if the water stays there. HA pulls water aggressively but releases it just as fast when ambient humidity drops. PGA’s film structure slows that release. So the 4x number is real, but the practical difference is even bigger in dry climates or air-conditioned rooms.
When Hyaluronic Acid Fails (And Why Nobody Talks About It)
HA isn’t bad. It’s just finicky. And most people use it in conditions where it backfires.
The problem is physics. HA draws water toward the highest concentration of HA molecules. If the air is dry—below 50% relative humidity—HA pulls water from the only available source: your skin. Instead of hydrating, it dehydrates. You applied it to fix dryness, and it made things worse.
This is why every HA product says “apply to damp skin.” That instruction isn’t a tip. It’s a warning. Without external water, HA turns on you.
PGA doesn’t have this failure mode. Its film traps whatever moisture is already there, plus whatever you layer underneath. It’s not aggressively pulling. It’s passively holding. In a dry office or on a winter day, PGA maintains hydration while HA gives it up.
COSRX’s Hyaluronic Acid Intensive Cream actually pairs HA with small amounts of PGA for this exact reason—the PGA compensates for HA’s evaporation problem. But if you want pure PGA performance, The Ordinary doesn’t make a dedicated PGA serum yet. The Inkey List owns this space at the drugstore level.
How to Layer PGA in a Routine Without Ruining Everything
Order matters. PGA goes last among your water-based products. Always.
Because PGA forms that hydrogel film, anything you apply after it won’t penetrate. Serums, treatments, active ingredients—they all need to go on first. PGA seals them in.
Here’s the sequence:
- Cleanse
- Active treatments (vitamin C, niacinamide, retinol—whatever you’re using)
- Thin, water-based serums
- PGA serum on slightly damp skin
- Moisturizer (optional, depending on your skin type)
- Sunscreen (morning)
The damp skin part still matters, though less critically than with HA. PGA needs some water to bind. If your skin is bone-dry, mist it first. The Inkey List PGA Serum works best with this approach—one pump, patted over damp skin, then wait 30 seconds before moisturizer.
A mistake people make: layering PGA under a heavy oil-based moisturizer. The oil can disrupt the hydrogel film. If you’re using facial oils, apply them before PGA, not after. Let the PGA be the final seal.
PGA vs. HA: A Direct Comparison Table
| Factor | Polyglutamic Acid (PGA) | Hyaluronic Acid (HA) |
|---|---|---|
| Water-binding capacity | ~4,000-5,000x its weight | ~1,000x its weight |
| Molecular weight | 1+ million Daltons | 50,000 to 2 million Daltons |
| Penetration | Surface only (forms film) | Minimal (mostly surface) |
| Evaporation risk in dry air | Low (film blocks TEWL) | High (pulls water from skin) |
| Occlusive effect | Moderate | None |
| Texture | Slightly tacky, slippery | Varies (watery to gel) |
| Best climate | Dry, cold, air-conditioned | Humid environments |
| Pairs well with | HA, glycerin, ceramides | PGA, glycerin, squalane |
| Key product example | The Inkey List Polyglutamic Acid Serum ($16, 3% PGA) | The Ordinary Hyaluronic Acid 2% + B5 ($9) |
Neither ingredient is universally better. But PGA wins for anyone in dry climates, anyone using retinoids (which compromise barrier function), and anyone who’s tired of their HA serum evaporating by lunchtime.
Who Should Skip PGA Entirely
If you live in Singapore. Or Miami. Or anywhere with 80%+ humidity year-round.
In high-humidity environments, the air is already saturated with moisture. Your skin isn’t losing water rapidly. Adding a film-forming humectant on top can feel heavy, sticky, and unnecessary. HA works beautifully in these conditions because there’s plenty of atmospheric water to pull from. PGA adds occlusion you don’t need.
Also: very oily skin types should test carefully. The film can trap sebum along with water. Some people report increased congestion with daily PGA use. Not acne exactly—more like a heavy, coated feeling that doesn’t fully absorb. If your skin already produces enough oil to form its own occlusive layer, adding PGA is redundant.
And if you’re using a moisturizer with petrolatum, dimethicone, or shea butter high on the ingredient list, you already have occlusion. PGA adds little. Save your money.
What to Actually Buy Right Now
The PGA market is still small. That’s good—fewer gimmicky products, more focused formulations.
The Inkey List Polyglutamic Acid Serum ($16 for 30ml) is the reference product. 3% PGA concentration, minimal ingredient list, no fragrance. It’s slightly tacky for about 90 seconds, then dries down to a smooth, primer-like finish. Works under makeup. Works over retinol. Hard to beat at this price.
If you want a combined HA + PGA product, Indeed Labs Hydraluron Moisture Jelly ($25) uses both humectants plus a phospholipid complex for barrier support. The texture is lighter than The Inkey List, better for combination skin.
For a K-beauty option, Isntree Hyaluronic Acid Water Essence ($22) lists sodium hyaluronate as the star but includes small amounts of polyglutamic acid in the base. Not a dedicated PGA product, but a good entry point if you’re experimenting.
One product to skip: anything listing PGA below the fifth ingredient while charging over $40. PGA is not expensive to formulate. The raw material costs more than HA but not dramatically so. A $60 PGA serum with fancy packaging is just branding.
Polyglutamic acid isn’t replacing hyaluronic acid. But it’s solving the specific failure that HA never could—holding water in place when the air refuses to cooperate. For anyone in dry climates, on drying medications, or simply exhausted by the constant reapplication cycle, it’s the more honest humectant.