Polyglutamic Acid Retains 45% Moisture vs. Hyaluronic Acid's 36% at 120 Minutes
Hyaluronic acid is treated as the reference standard for skin hydration. The claim that it absorbs up to 1,000 times its weight in water has become the benchmark for the category. Polyglutamic acid (PGA) claims to hold five times that amount. A January 2025 study tested that claim at both the cellular level and in a reconstructed skin model.
Bacillus subtilis from Jeju Wetland
The research team focused on the organism responsible for producing polyglutamic acid. The Bacillus subtilis strain HB-31 was isolated from Gotjawal Wetland on Jeju Island, South Korea, and confirmed to produce high-molecular-weight gamma-polyglutamic acid (γ-PGA) in quantities viable for commercial production.
γ-PGA is a polymer made of glutamic acid monomers connected by peptide bonds. Unlike hyaluronic acid, which is a disaccharide repeating structure, γ-PGA is an amino acid-based water-soluble polymer. The structural difference changes how each molecule binds and holds water.
Skin Barrier Gene Activation
The central finding was barrier marker expression. When keratinocytes were treated with γ-PGA, the mRNA expression of three core skin barrier proteins, filaggrin, involucrin, and loricrin, increased dose-dependently. Related enzymes involved in lipid synthesis, serine palmitoyl transferase, fatty acid synthase, and HMG-CoA reductase, were also upregulated.
A functional skin barrier depends on three pillars: structural proteins, a ceramide-based lipid matrix, and natural moisturizing factors. γ-PGA treatment stimulated pathways across all three.
Hyaluronic acid synthase genes (HAS-1, HAS-2, HAS-3) were also upregulated, meaning γ-PGA does not just attract water from outside. It signals skin cells to produce more hyaluronic acid internally. Aquaporin 3 (AQP3), the channel protein involved in water transport, was similarly elevated.
In a reconstructed skin model with 1% γ-PGA application, filaggrin, involucrin, CD44, and aquaporin 3 all increased significantly versus controls (p<0.05).
Moisture Retention: 120-Minute Comparison
In the water retention assay, γ-PGA formulations achieved 45% moisture retention at 120 minutes, compared to 40% in the untreated control and 36% in the hyaluronic acid reference formulation. The nine percentage point difference over HA represents a meaningful gap in sustained surface hydration.
The mechanism is structural. γ-PGA’s high molecular weight means it stays predominantly on the skin surface, forming a film that slows transepidermal water evaporation. High-molecular-weight HA functions similarly, but γ-PGA maintains this film more durably over time.
PGA Does Not Replace HA, It Enhances It
A more accurate framing than “better than hyaluronic acid” is that γ-PGA complements it. Research shows γ-PGA inhibits hyaluronidase activity, the enzyme that breaks down hyaluronic acid in skin, meaning hyaluronic acid applied alongside γ-PGA lasts longer. This synergistic effect is already driving formulation trends toward combination serums featuring both ingredients.
The Natto Connection
γ-PGA is the compound responsible for natto’s characteristic stringiness and viscosity. As a refined cosmetic ingredient, it retains the surface-forming properties without the odor or tactile heaviness of fermented soybean. In serum and essence formats, it creates a light hydrating veil on the skin surface, well-suited to humid-climate routines or environments where HA might paradoxically pull moisture from the skin into the air.
The standard for choosing a humectant is shifting from “how much water does it absorb” to “does it help skin produce and retain its own moisture.” γ-PGA addresses both questions.