Chemically, glutathione is a tripeptide, or a molecule composed of three amino acids (glutamate, cysteine, and glycine). Glutathione's importance as a free radical scavenger derives from two characteristics.

First, it is extremely abundant - perhaps the most abundant low-molecular-weight peptide in the body.

Second, it plays a central role in the glutathione redox cycle, a complex biochemical system involved in neutralizing free radicals and providing protection from free hydroperoxides and lipid peroxides. In addition, glutathione recycles other well-known antioxidants (especially vitamin E), keeping them in their active state.

As humans age, glutathione levels drop, and the ability to detoxify free radicals decreases.