Polyglutamic Acid

Polyglutamic acid's main advantage over other humectants comes down to sheer water-holding capacity — some research suggests it can retain several times more moisture than hyaluronic acid at an equivalent concentration, largely because of its molecular structure and film-forming properties on skin's surface. That film also helps reduce transepidermal water loss, meaning it's not just pulling in moisture but actively slowing how quickly skin loses it again, which is a slightly different mechanism than a pure humectant like glycerin.

Because it's produced through fermentation rather than synthesized or animal-derived, it also fits cleanly into routines built around fermented Korean skincare ingredients, and its smooth, slightly cushioned finish is often noted as more comfortable than some hyaluronic acid formulas that can feel tacky as they dry down.

It suits dry, dehydrated or environmentally stressed skin especially well, and works particularly well for anyone who finds hyaluronic acid alone insufficient or who wants an extra layer of moisture retention without adding a heavier cream. It's also a reasonable addition for skin recovering from a dehydrating treatment, like a strong exfoliating acid or retinol, since it can help offset some of that dryness during the adjustment period.

The catch every humectant shares. PGA works by pulling water in and holding it there — but in a dry room or a low-humidity climate, there may not be enough water in the air to pull from, and a humectant can end up drawing moisture out of deeper skin instead. That's why it belongs on damp skin with something occlusive over the top, and why people in dry climates sometimes report a humectant making their skin feel worse rather than better. It isn't a fault in the ingredient; it's a fault in how it's being used.

Polyglutamic acid won't treat acne, pigmentation or texture on its own, so it's best understood as a hydration-focused ingredient rather than a corrective one. Reactions are uncommon, though anyone with a soy allergy should check the specific source used in a given formula.

Polyglutamic acid works best applied to damp, not dry, skin, since humectants perform better when there's already moisture present to draw from — pat it on right after cleansing or toning while skin is still slightly damp, then seal it in with a moisturizer before it has a chance to evaporate.

It layers comfortably with hyaluronic acid, niacinamide, retinol and most other ingredients, since it doesn't carry meaningful irritation risk on its own and can actually help offset the dryness that comes with introducing a new active.

There's no cycling or gradual introduction required, so daily use, morning and night, is standard.

In very dry or low-humidity conditions, follow it immediately with an occlusive like squalane. This is the step that decides whether a humectant helps or hurts, and it's the one most often skipped.