Dihydroxyacetone
The "tanning agent" in many self-tanning formulas. It is actually a Keto sugar that reacts with protein on the surface of the skin to create the look of a tan. The molecules in this ingredient are too large to penetrate the skin any deeper than the top-most layer. Since it is unable to react in any way with the Melanin in the skin, this ingredient does not afford the protection from sun that a real tan would.