How does a self-tanning cream alter skin color from a biochem perspective?

What is actually happenning, biochemically, that alters your skin color when you rub Betty%26#039;s Magic Bahamas Bronzing Tanner on your a-ss?|||Oxidization....think about an apple or a banana turning brown after being exposed to air....same thing.|||Dunno ,tried it once , missed some spots (you cant tell until a couple hrs later) I looked like a orange and white zebra Yeah waay sexy..... NOT!