Algin

What it is

Algin is the sodium salt of alginic acid, extracted from brown seaweeds such as kelp. In the presence of calcium salts it sets rapidly into a soft rubber, which is the basis of the powder-and-water "modelling" or "rubber" masks used in salons. In ordinary leave-on products it simply acts as a thickener and helps a formula stay where you put it.

How it shows up on a label

What it does well

• Forms a physical gel that holds water and other ingredients against the skin

  The gelling behaviour is well-characterised chemistry used across food, wound dressings and cosmetics. It slows evaporation during a mask session, which is why skin feels more hydrated afterwards; the alginate itself is not absorbed.

  Moderate evidence

Worth knowing

• Does nothing active on its own

  Alginate is a texture ingredient. Any benefit from a rubber mask comes from occlusion during wear and from whatever active ingredients are mixed in with it.

  Matters most toAnyone paying salon prices for a modelling mask on the strength of the alginate itself.

Where the EU stands

Sources (1)

Every link goes to the original: a journal, a PubMed record or an EU document.

1. [1]
   Safety Assessment of Polysaccharide Gums as Used in Cosmetics (Final Report)

   Cosmetic Ingredient Review (CIR) Expert Panel · 2015

   The Expert Panel reviewed 106 polysaccharide gums used as viscosity increasing agents and concluded that 105 of them - algin, the sodium salt of alginic acid, among the linear polysaccharides named in the conclusion - are safe in the present practices of use and concentration in cosmetics. The Panel also asked industry to use good manufacturing practice to limit impurities from the agents used to modify polysaccharide gums.