PGA / γ-PGA / Natto Gum
A water-soluble biopolymer of chained glutamic-acid units, produced by bacterial fermentation (classically the natto fermentation of soybeans). As a humectant it binds water at the skin surface and forms a light film that slows evaporation, so it's best understood as a companion to — not a replacement for — hyaluronic acid: HA draws water into deeper layers, PGA helps hold it at the surface. Its larger molecular size means it stays more superficial than low-weight HA.
PGA works at low percentages — typically 0.1–1%, sitting at or below the 1% line, which is expected for a high-performance humectant. Below the 1% line isn't fairy-dusting here; humectant polymers do real work at low doses. It layers well over a hydrating toner and under an occlusive moisturiser that seals the water in.
Apply 0.1–1% to damp skin, AM and/or PM, then seal with a moisturiser so the bound water doesn't simply evaporate. It pairs naturally with hyaluronic acid and glycerin. In very dry air, the occlusive you layer on top matters more than the humectant itself.
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