Thioctic Acid

Better known as alpha lipoic acid. Its structure is amphiphilic — a fatty tail with a sulphur-containing ring at one end and an acid group at the other — so it partitions into both the watery and the oily parts of skin rather than being confined to one. The body makes small amounts of it, where it functions in energy metabolism. In skincare it is used purely as an antioxidant, and it is one of the better-studied antioxidants used topically, though most of the mechanistic work is laboratory rather than clinical.

Antioxidant. For the Look of Scars

It neutralises free radicals directly. Once reduced in the body to dihydrolipoic acid it can also help restore other antioxidants — regenerating vitamin C directly, and vitamin E indirectly through it — which is why it is described as part of an antioxidant network. Most of that evidence is laboratory work rather than topical trials. Its ability to act in both watery and oily environments is the practical advantage, since most antioxidants are limited to one or the other. It is unstable in formulation and can sting on sensitive skin, so it is usually included at modest levels.