Polyglutamic acid (PGA) is a water-soluble biopolymer made up of glutamic acid units linked together in a chain, produced naturally by certain bacteria during fermentation. It shows up most often in skincare products as a humectant, marketed for its ability to hold moisture against the skin, but its uses extend well beyond serums and moisturizers. The molecule has drawn research interest in medicine, agriculture, and environmental cleanup, and the science behind it is more varied than the typical ingredient spotlight suggests.
What PGA Actually Is
Polyglutamic acid, specifically poly-gamma-glutamic acid (γ-PGA), is an anionic polymer made of repeating glutamic acid subunits. It is produced and secreted by several microorganisms, especially species of Bacillus bacteria.1PubMed. Building a circular economy around poly(D/L-γ-glutamic acid)- a smart microbial biopolymer If you eat natto, the sticky, stringy Japanese fermented soybean dish, you have already encountered it. That viscous, web-like texture is largely γ-PGA produced by Bacillus subtilis during fermentation.
The “poly” part means it is a long chain of many glutamic acid molecules. The “gamma” refers to which bond connects each unit to the next. Unlike most proteins, where amino acids link at the alpha position, PGA links at the gamma carboxyl group, giving it an unusual backbone that resists the enzymes that normally break down proteins. This is partly why it is so stable on your skin and in other applications. It can exist as a chain of all L-glutamic acid units, all D-glutamic acid units, or a mix of both.2PubMed Central. Poly (γ) glutamic acid: a unique microbial biopolymer with diverse commercial applicability
Commercially, PGA is produced through bacterial fermentation, typically using Bacillus strains grown on nutrient-rich substrates. Researchers have explored cost-effective production using agricultural waste materials and food-industry byproducts. One study demonstrated that dairy manure compost and monosodium glutamate production residues could serve as cheap fermentation substrates, yielding PGA with a molecular weight above 130 kilodaltons.3Bioresource Technology. Optimization of the production of poly-γ-glutamic acid by Bacillus amyloliquefaciens C1 in solid-state fermentation using dairy manure compost and monosodium glutamate production residues as basic substrates Advanced purification methods using membrane filtration can recover over 95% of unconverted raw materials, making large-scale production increasingly efficient.4PubMed. Fermentative production of poly (γ-glutamic acid) from renewable carbon source and downstream purification through a continuous membrane-integrated hybrid process
How It Works on Skin
PGA’s main selling point in skincare is hydration. The molecule is a humectant, meaning it pulls water from the environment and holds it at the skin’s surface. Because of the many carboxyl groups dangling off its chain, each repeating unit can attract and bind water molecules, creating a thin hydrating film. This mechanism is straightforward and well-supported: PGA is hygroscopic, and that hygroscopy translates to a moisturizing effect when you apply it topically.
But the story does not stop at surface-level moisture. A 2025 study tested PGA on keratinocytes, the cells that make up most of the outer skin layer, and on a reconstructed skin model. PGA-treated keratinocytes showed increased expression of filaggrin, involucrin, and loricrin in a dose-dependent manner. These are proteins involved in building and maintaining the skin barrier, the outermost layer that keeps moisture in and irritants out.5PubMed Central. Poly-γ-Glutamic Acid from a Novel Bacillus subtilis Strain: Strengthening the Skin Barrier and Improving Moisture Retention in Keratinocytes and a Reconstructed Skin Model In plain terms, PGA appears to do more than just sit on top of your skin holding water. It may signal skin cells to strengthen their own defenses, at least in lab settings.
This barrier-support angle is what makes PGA interesting compared to a generic humectant like glycerin. If it genuinely upregulates barrier proteins in real-world use, it could help people with compromised barriers, such as those dealing with dryness, eczema-prone skin, or irritation from retinoids. That said, the gap between a cell culture study and your bathroom mirror is large, and human clinical trials specifically measuring barrier improvement from PGA are still sparse.
PGA Versus Hyaluronic Acid
Skincare marketing frequently frames PGA as a superior alternative to hyaluronic acid (HA), sometimes claiming it holds several times more moisture. The two molecules work similarly as humectants, but they are structurally different. HA is a glycosaminoglycan, a sugar-based polymer, while PGA is an amino-acid-based polymer. Both are large, water-attracting molecules, and both form hydrating films on skin.
Interestingly, research suggests the two may work better together than either does alone. A study examining blends of cellulose nanofibrils, HA, and PGA found that the system combining all three polymers was the most effective at enhancing water-holding performance.6Cellulose. Synergistic moisturizing effect of a cellulose nanofibril/hyaluronic acid/poly-γ-glutamic acid blend system The takeaway for your routine is that PGA and HA are not rivals. They complement each other, and formulations containing both can retain more moisture than those containing just one. If your serum or moisturizer lists both ingredients, that is a feature, not redundancy.
Where PGA may have a practical advantage is texture. HA at high molecular weights can feel tacky or leave a film that pills under makeup. PGA tends to feel lighter and absorbs more cleanly. For people who dislike the sticky feel of concentrated HA serums, PGA serums may offer similar hydration with a more pleasant skin feel.
Side Effects and Safety
PGA has a strong safety profile in the research that exists. It is a naturally occurring compound, biodegradable, and has been consumed in natto for centuries without reports of harm. In topical skincare concentrations, adverse reactions are rare. Most people tolerate it well, including those with sensitive skin.
Animal safety testing reinforces this picture. A study using PGA-gelatin composite hydrogels on guinea pigs found that the material was neither allergenic nor a dermal sensitizer.7PubMed. Gamma-poly glutamate/gelatin composite hydrogels crosslinked by proanthocyanidins for wound healing When cross-linked PGA particles were tested as injectable dermal fillers in a more invasive application, local redness and swelling from the injection resolved within roughly two weeks. No tissue death or systemic allergic reactions were observed, and the filler actually promoted local collagen formation.8PubMed. Preparation, function, and safety evaluation of a novel degradable dermal filler, the cross-linked poly-γ-glutamic acid hydrogel particles
That said, there are a few practical caveats worth noting. First, “polyglutamic acid” on an ingredient label does not tell you the molecular weight, the concentration, or what other ingredients surround it. Reactions to a PGA product could stem from fragrance, preservatives, or other actives in the formula rather than the PGA itself. Second, because PGA is highly water-attracting, using it in very dry environments without an occlusive layer on top could theoretically draw moisture from deeper skin layers rather than the air, the same concern that applies to HA. This is a theoretical risk more than a documented one, but layering a cream or oil over your PGA serum in arid conditions is sensible practice.
One formulation consideration that matters behind the scenes: PGA’s behavior changes significantly with pH. At certain pH levels, it can form insoluble complexes when mixed with other charged polymers, which affects product stability.9PubMed. Characterization of electrostatic interactions and complex formation of É£-poly-glutamic acid (PGA) and É›-poly-l-lysine (PLL) in aqueous solutions This is more a concern for formulators than for consumers, but it means that the effectiveness of PGA in a finished product depends heavily on how well the product was designed. A poorly formulated PGA serum might not deliver its benefits as expected.
Calcium Absorption and Dietary PGA
Beyond skincare, PGA has an intriguing dietary benefit that gets almost no consumer attention. When consumed orally, as it is in natto, PGA appears to increase calcium absorption in the gut. The mechanism is straightforward: PGA prevents calcium from forming insoluble complexes with phosphate in the intestine, keeping the calcium in a soluble form that the body can actually absorb.
A rat study found that natto mucilage containing PGA significantly increased both the amount and percentage of soluble calcium in the lower small intestine compared to diets with soy protein, plain natto, or mucilage-free natto.10Bioscience, Biotechnology, and Biochemistry. Natto Mucilage Containing Poly-γ-glutamic Acid Increases Soluble Calcium in the Rat Small Intestine Moving from rats to humans, a study in postmenopausal women tested PGA directly. Average calcium absorption with PGA was about 39%, compared with roughly 35% without it. The benefit was even more pronounced in women who started with below-average calcium absorption.11PubMed. Acute effect of poly-gamma-glutamic acid on calcium absorption in post-menopausal women
A roughly four-percentage-point increase in calcium absorption might not sound dramatic, but for populations at risk of osteoporosis, even modest improvements in calcium uptake can matter over time. This finding also offers a concrete nutritional reason to eat natto, beyond its better-known vitamin K2 content. Whether isolated PGA supplements could replicate this benefit at scale is an area that has not been widely studied in large human trials.
Wound Healing and Biomedical Research
PGA has properties that make it useful far beyond cosmetics. In biomedical research, it is being developed into hydrogels for wound healing. These are gel-like materials that can be placed on a wound to keep it moist, absorb fluid, and support tissue repair.
A PGA-based hydrogel combined with polylysine achieved an 86% wound healing rate within seven days in animal studies, compared to 67% in controls. The hydrogel worked by tamping down the inflammatory response, reducing levels of the inflammatory marker IL-6, promoting blood vessel growth, and speeding up collagen deposition. It fully biodegraded within 21 days without triggering significant inflammation.12PubMed Central. A Poly-γ-Glutamic Acid/ε-Polylysine Hydrogel: Synthesis, Characterization, and Its Role in Accelerated Wound Healing Another PGA-based hydrogel, designed with polyethyleneimine, showed strong blood absorption and clotting ability, making it a candidate for hemostatic wound dressings, the kind used to stop bleeding in surgical or emergency settings.13PubMed Central. Multifunctional Hydrogels Based on γ-Polyglutamic Acid/Polyethyleneimine for Hemostasis and Wound Healing
PGA nanoparticles are also being explored as drug delivery vehicles. Because PGA is water-soluble, biodegradable, and nontoxic, it can be cross-linked into nanoparticles that carry drugs to specific targets in the body. One system paired PGA with folic acid as a targeting agent and doxorubicin (a chemotherapy drug) as the payload, creating nanoparticles designed to seek out cancer cells that overexpress folate receptors.14Journal of Drug Delivery Science and Technology. Crosslinked poly-γ-glutamic acid based nanosystem for drug delivery A review of these systems noted that PGA nanoparticles enhance drug stability and provide a slow-release effect, all while being straightforward to prepare.15PubMed. Preparation, Characterization and Drug Delivery Research of γ-Polyglutamic Acid Nanoparticles: A Review
None of these biomedical applications are in your pharmacy yet. They are at the preclinical or early-development stage. But they help explain why PGA has attracted so much research attention: it is biodegradable, safe, easy to modify chemically, and can be produced cheaply through fermentation. That combination of traits makes it a versatile platform for medical materials.
Agricultural Uses
One of PGA’s most commercially significant applications has nothing to do with human skin or health. In agriculture, PGA functions as a water-retaining agent and biostimulant, and the evidence here is genuinely impressive.
PGA absorbs and holds large amounts of water in soil, which helps plants survive drought. A study on maize seedlings showed that PGA fermentation broth significantly increased seedling biomass, soil water content, and microbial activity in the soil. It improved drought resistance by keeping soil moisture higher and supporting a healthier community of bacteria and fungi around the roots.16Applied Soil Ecology. Poly-γ-glutamic acid improves the drought resistance of maize seedlings by adjusting the soil moisture and microbial community structure When researchers went further and engineered maize plants to produce PGA internally, those transgenic plants showed about a 50% increase in ear length, ear weight, and grain weight under drought stress compared to controls.17PubMed. Heterologous synthesis of poly-γ-glutamic acid enhanced drought resistance in maize (Zea mays L.)
PGA also improves nutrient availability in soil. A study on grassland sandy soil found that PGA acted as a biostimulant, increasing the availability of potassium, zinc, manganese, iron, calcium, magnesium, and nitrogen compounds. Plants grown with PGA developed longer roots, greater aboveground biomass, and better resprouting capacity after stress.18Scientific Reports. Effects of γ-polyglutamic acid on grassland sandy soil properties and plant functional traits exposed to drought stress Because PGA biodegrades naturally, it does not accumulate in soil the way synthetic polymers do, making it a more environmentally friendly alternative to traditional super-absorbent polymers used in agriculture.
Environmental and Industrial Applications
PGA’s ability to bind charged particles makes it useful for cleaning contaminated water. As a bioflocculant, it can clump together suspended particles in water, causing them to settle out. One study testing PGA as a coagulant for raw water treatment found that its performance was superior to conventional chemical coagulants.19Journal of Environmental Chemical Engineering. Physicochemical characterization and evaluation of PGA bioflocculant in coagulation-flocculation and sedimentation processes Since PGA is biodegradable, it avoids the environmental concerns associated with synthetic flocculants like polyacrylamide.
PGA-based hydrogels have also been tested for heavy metal removal from wastewater. A recyclable PGA hydrogel was shown to adsorb copper ions through electrostatic interactions, with adsorption capacity increasing at higher pH as more binding sites became available. The process was spontaneous and worked better at lower temperatures. The hydrogel could be regenerated and reused, making it a cost-effective material for removing heavy metals from industrial wastewater.20PubMed Central. Heavy Metal Removal from Wastewater Using Poly(Gamma-Glutamic Acid)-Based Hydrogel The copper adsorption capacity was modest compared to some other biosorbents like modified chitosan, but the recyclability and ease of use give PGA-based gels a practical edge in certain applications.
Who Should Consider PGA in Skincare
If you have dry or dehydrated skin and are looking for a humectant that feels lighter than hyaluronic acid, PGA is worth trying. It layers well under other products, plays nicely with most active ingredients, and is unlikely to irritate. People with sensitive or reactive skin who struggle with heavier humectants may find PGA serums more comfortable.
For those already using HA and happy with it, PGA is not a necessary upgrade. The evidence does not clearly show that one is dramatically superior to the other for surface hydration. The barrier-strengthening data from cell studies is promising but preliminary. If you are drawn to products that contain both, the synergy data supports that combination.
People interested in PGA for dietary calcium benefits would get the most natural exposure through eating natto, which provides PGA alongside fermented soy’s other nutrients. Isolated PGA supplements marketed for calcium absorption exist in some markets, particularly in Japan and South Korea, but large-scale human trials confirming their long-term bone health benefits have not been published. The postmenopausal calcium absorption data is encouraging and directionally clear, but it comes from a small study measuring an acute effect rather than years of supplementation.
If your interest runs toward gardening or small-scale agriculture, PGA-based soil amendments are commercially available in some regions and function as biodegradable water-retention aids. They are particularly useful in sandy soils or drought-prone areas where holding onto moisture around roots makes a measurable difference in plant survival and growth.