How does fake tan work?

Today, the majority of sunless tanning lotions, mousses, sprays and gels contain a safe sugar molecule called dihydroxyacetone (DHA), which darkens skin tone with no side effects.

The concentration of the DHA determines the darkness of the fake tan. DHA reacts with the amino acids present in dead cells on the surface of the skin to alter their colour, producing a yellow/brown tanned appearance. The colour doesn’t come through straight away, however; it develops over a number of hours and often keeps getting darker for 24 hours. Further application of the tanning lotion over a number of days will create a darker tone. Because the tan only affects the already-dead surface skin cells, the colour will of course fade and wear off as the skin is eventually shed.