Ingredient that affects the color of skin and that is present in most self-tanners. Derived from sugar, it reacts with amino acids found in the top layers of skin to create a shade of brown; the effect takes place within two to six hours and it can build color depth with every reapplication. It has a long history of safe use when applied topically to skin, where it affects only the uppermost layers. Dihydroxyacetone doesnŠ—Èt pose a health risk to skin.

References for this information:

Journal of the American Academy of Dermatology, May 2004, issue 5, pages 706-713