Polyglutamic acid (PGA) is a naturally occurring biopolymer made from repeating units of the amino acid glutamic acid. It has gained attention in skincare for its extraordinary ability to hold moisture, with lab measurements showing it can absorb up to 731 times its weight in water in pure form. Some estimates place its water-retention capacity at up to 5,000 times its weight, making it one of the most powerful humectants available in skincare products.
Where Polyglutamic Acid Comes From
PGA isn’t synthesized in a lab from scratch. It’s produced through bacterial fermentation, most commonly by species of Bacillus bacteria. Bacillus subtilis and Bacillus licheniformis are the two most widely used strains in industrial production. If you’ve ever eaten natto, the sticky, fermented soybean dish popular in Japan, you’ve already encountered polyglutamic acid. That characteristic slimy, stringy texture is largely due to PGA produced by Bacillus subtilis during fermentation.
Chemically, PGA is classified as a polyamide, a chain of amino acids linked together. The specific form used in most applications is gamma-polyglutamic acid, meaning the glutamic acid units connect at a particular position on the molecule. This structure gives PGA its unique water-binding and film-forming properties.
How It Works on Skin
PGA is a large molecule, significantly larger than hyaluronic acid. Because of its size, it doesn’t penetrate deep into the skin. Instead, it sits on the surface and forms a thin, moisture-retaining film. This film does two things: it pulls water from the environment toward your skin, and it reduces the amount of moisture that evaporates from the layers beneath.
Beyond surface hydration, PGA has a secondary mechanism that makes it especially interesting. It inhibits hyaluronidase, the enzyme responsible for breaking down hyaluronic acid that your skin naturally produces. By slowing this degradation process, PGA helps your skin hold onto its own hyaluronic acid longer, which supports elasticity and plumpness from the inside out. This means PGA doesn’t just add moisture on top of your skin; it helps preserve the moisture system your body already has.
Polyglutamic Acid vs. Hyaluronic Acid
The comparison with hyaluronic acid (HA) comes up constantly, and the two ingredients work differently enough that they complement rather than replace each other. Hyaluronic acid can retain about 1,000 times its weight in water, while polyglutamic acid can retain up to 5,000 times its weight. On raw water-holding power alone, PGA wins by a wide margin.
The key difference is where each one works. Low molecular weight hyaluronic acid is small enough to penetrate deeper into the outer layers of skin, reaching the base of the epidermis. Once there, it can stimulate your body’s own production of hyaluronic acid. PGA, with its larger molecular size, stays on the surface and works as a barrier and humectant from the outside. Think of hyaluronic acid as working from within the skin’s upper layers and polyglutamic acid as working on top of them.
This is why many skincare formulations include both. Applying hyaluronic acid first allows it to absorb into the skin, and layering PGA over it creates a moisture-locking seal on the surface. The PGA also protects the hyaluronic acid beneath by inhibiting the enzyme that would break it down.
Who It Works Best For
PGA is particularly useful for people with dry or dehydrated skin who feel that hyaluronic acid alone isn’t enough. Because it forms a surface film rather than absorbing into deeper layers, it provides a noticeable, immediate smoothing and plumping effect. People with mature skin may also benefit from the enzyme-inhibiting action, since hyaluronidase activity increases with age, meaning your skin breaks down its natural hyaluronic acid faster over time.
If you have oily skin, the film-forming quality of PGA can feel slightly heavier than hyaluronic acid alone. It’s not greasy, but it does leave a more tangible layer. Some people find this pleasant and describe it as a “dewy” finish, while others with already oily skin may find it excessive, especially under makeup.
Safety and Potential Reactions
PGA is generally well tolerated, and because it sits on the surface of the skin rather than penetrating deeply, it tends to cause fewer issues than ingredients that absorb into lower layers. That said, allergic reactions are possible with any new product. Symptoms to watch for include redness, itching, hives, burning, dryness, or blistering.
A simple patch test is the easiest way to check. Apply a small amount to the inside of your forearm or behind your ear and wait 24 hours. If nothing happens, you’re likely fine to use it on your face. Keep in mind that reactions can also come from other ingredients in the product, not just the PGA itself, so switching brands before giving up on the ingredient entirely is worth trying.
How to Use It in Your Routine
PGA typically comes as a serum or is included in moisturizers. In a layered routine, apply it after thinner, more penetrating products like hyaluronic acid serums or vitamin C, and before heavier creams or oils. Because it forms a film, anything applied after PGA may not absorb as effectively, so order matters.
You can use PGA both morning and night. In the morning, it works well under sunscreen, helping to lock in moisture throughout the day. At night, it pairs naturally with richer moisturizers to reduce overnight water loss. There’s no known issue with combining PGA with common active ingredients like retinol, niacinamide, or vitamin C, making it one of the more flexible hydrating ingredients to incorporate.