The Chemistry of Fake Tan

There are two chemicals that are incorporated in tanning lotion: dihydroxyacetone (DHA) and erythrulose.  The dihydroxyacetone is the most commonly used chemical in tanning lotion.  The FDA  allowed the use of DHA in tanning lotions in the year 1977, but it is not allowed to be used in tanning booths. There are 3 simple steps in how one can obtain a fake tan.  Step 1 is apply the tanning lotion with the DHA that will react with the amino acids in the dead layer on the skin's surface.  Step 2 is that a certain reaction will take place (Maillard reaction - the reaction that is often seen in baking and roasting foods when cooking).  And finally, step 3, is the reaction that melanoidins start to be produced which are the chemicals needed that cause the actual tan.

FUN FACTS:

• The impact of dihydroxyacetone isn't immediately effective since it takes about 2-4 hours for the browning effect to activate and it can continuously darken your skin for up to 72 hours.  
• Tanning lotions can actually contain up to 15% DHA, but the lotions you typically buy in store would be topped at 5% and can go as low at 3%.
• The reason it is not prohibited in spray tanning booths is because of the dangerous effects it can cause to your body when you ingest or inhale DHA (damaged DNA in bacteria cells)

Article Link