Polyglutamic acid (PGA) is a water-soluble biopolymer produced by bacterial fermentation, now widely used in skincare for its ability to hold up to 5,000 times its weight in water. That makes it roughly four times more effective at retaining moisture than hyaluronic acid, the ingredient it’s most often compared to. If you’ve seen it on a serum label and wondered what it actually is and whether it’s worth adding to your routine, here’s what the science says.
Where Polyglutamic Acid Comes From
PGA is a naturally occurring polymer made of repeating units of glutamic acid, an amino acid your body already produces. In nature, bacteria in the Bacillus family, particularly Bacillus subtilis and Bacillus licheniformis, produce it during fermentation. If you’ve eaten natto, the sticky Japanese fermented soybean dish, you’ve already encountered PGA: it’s the compound responsible for that characteristic stringy texture.
For commercial skincare, PGA is manufactured through controlled bacterial fermentation rather than extracted from food. The resulting molecule can range dramatically in size, from 50,000 to 2 million Daltons in molecular weight, and that size determines how it behaves on your skin.
How It Works on Skin
PGA functions as a humectant, meaning it pulls water from the environment and binds it to the skin’s surface. But it does more than just sit there holding moisture. Higher-molecular-weight forms create a thin, breathable film that reduces transepidermal water loss, the gradual evaporation of moisture through your skin throughout the day. Lower-molecular-weight forms can penetrate deeper into the outer skin layers, binding water molecules from within.
Beyond simple hydration, PGA appears to support your skin’s own moisture-producing systems in two ways. First, it boosts the production of hyaluronic acid by increasing the activity of the enzymes (hyaluronic acid synthases) responsible for making it. Second, it promotes the expression of aquaporin 3, a channel protein that helps transport water through skin cells. In other words, PGA doesn’t just add moisture on top of your skin. It helps your skin generate and move more moisture on its own.
There’s also evidence that PGA inhibits hyaluronidase, the enzyme that breaks down hyaluronic acid in the skin’s deeper layers. This means it may help preserve the hyaluronic acid your skin already has, slowing its natural degradation.
PGA vs. Hyaluronic Acid
The comparison is inevitable since both are hydrating ingredients, but they work differently enough to complement each other rather than compete. Hyaluronic acid holds up to 1,000 times its weight in water. PGA holds up to 5,000 times its weight. That raw number is impressive, but the practical difference is more nuanced: PGA’s film-forming properties give it stronger staying power on the skin’s surface, so hydration lasts longer rather than simply being more intense at the moment of application.
Hyaluronic acid, especially in low-molecular-weight forms, penetrates more readily into the skin. PGA tends to work more at the surface level (unless formulated with smaller molecules), creating that occlusive layer while also supporting your skin’s barrier function. Many skincare routines now use both: hyaluronic acid first to draw moisture into the skin, then PGA on top to seal it in and slow evaporation.
Effects on Texture and Fine Lines
The film PGA forms on the skin’s surface creates an immediate smoothing effect, which is why many users notice softer skin and less visible fine lines after a single application. This isn’t permanent structural change. It’s the result of well-hydrated skin cells plumping up and the thin polymer layer evening out the surface texture. Over time, the sustained hydration and increased hyaluronic acid production can contribute to more lasting improvements in skin elasticity, but the most noticeable results come from consistent daily use rather than occasional application.
How to Use It in Your Routine
PGA serums are typically formulated at concentrations around 3%, which is enough to deliver noticeable hydration without feeling heavy or sticky. The texture is lightweight and slightly viscous, similar to a thin gel.
The general rule for layering skincare is thinnest to thickest, and PGA serums usually work best as your last serum step before moisturizer. A practical routine looks like this:
- Cleanser
- Actives (vitamin C, retinol, exfoliants)
- Hyaluronic acid serum (if using)
- Polyglutamic acid serum
- Moisturizer
- Sunscreen (morning only)
Apply a pea-sized amount and pat it gently into your face and neck. You can use it both morning and evening. PGA is compatible with the most common active ingredients in skincare, including vitamin C, retinol, and chemical exfoliants. Its film-forming properties can actually enhance the performance of other actives by helping them stay in contact with the skin longer rather than evaporating.
Skin Types and Tolerability
PGA is well tolerated across skin types, including sensitive skin. Because it’s derived from an amino acid your body naturally produces, allergic reactions are rare. It’s non-comedogenic, so it’s unlikely to clog pores, and its lightweight texture makes it comfortable for oily skin types who find heavier hydrators too much. For dry or dehydrated skin, layering it over hyaluronic acid and under a richer moisturizer creates a multi-level hydration strategy that addresses both surface dryness and deeper moisture loss.
People with very oily skin sometimes find that PGA alone provides enough hydration to skip a traditional moisturizer, though this depends on climate and individual skin needs. In humid environments, humectants like PGA perform especially well because there’s more atmospheric moisture available for them to pull toward the skin.