Thioctic acid, also known as lipoic acid or alpha lipoic acid (ALA), is an organosulfur compound derived from caprylic acid (octanoic acid). ALA is made in animals normally, and is essential for aerobic metabolism. It is also manufactured and is available as a dietary supplement in some countries where it is marketed as an antioxidant. When applied to the skin, thioctic acid is considered to be a very potent antioxidant.

Thioctic acid is unique in that it is both water and oil soluble, unlike most antioxidants. Furthermore, thioctic acid has the capability of regenerating endogenous antioxidants such as glutathione, vitamin C, and vitamin E. All of these antioxidants work together to protect the skin from free radicals, the unstable molecules that contribute to the formation of premature wrinkles and fine lines on the skin. Upon application, thioctic acid first concentrates in the cell plasma membrane, where it neutralizes free radicals.Then, it moves on to the watery interior of the cell, known as the cytosol, where it can also stop the activity of free radicals and prevent activation of other pro-inflammatory chemicals. Due to its potent antioxidant properties, thioctic acid is often used in anti-aging skin care products.