Polyglutamic acid is a water-soluble polymer built from chains of glutamic acid, an amino acid. It is produced by bacterial fermentation and is best known as the substance that gives natto, a fermented soybean food, its characteristic viscosity.
How it works
Like hyaluronic acid, polyglutamic acid holds water through hydrogen bonding along its chain. Its capacity is frequently quoted as several times that of hyaluronic acid, though those figures come from laboratory measurements of the raw material rather than from formulated products at realistic use levels, so they are worth treating carefully.
Its more distinctive property is film formation. Polyglutamic acid dries to a light, flexible film on the skin surface, which reduces the rate at which water evaporates. That makes it partly occlusive as well as humectant, which sets it apart from hyaluronic acid, which is almost purely humectant.
Alongside hyaluronic acid
The two are frequently formulated together because their behaviour differs. Hyaluronic acid draws and holds water within the upper layers. Polyglutamic acid holds water at the surface and slows its loss. Neither is a substitute for the other.
In formulation
It is a large molecule and remains at the surface rather than penetrating. It is stable across a broad pH range and used at low concentrations, where it also contributes a smooth slip to the texture of a formula.
