Have you ever wondered how fake tan lotion manages to turn people's skin brown without subjecting them to UV radiation exposure? Actually, it's a chemical reaction that you observe all the time...whenever someone is cooking meat.
Writing over at his blog, Compound Interest [rimshot], British chemistry teacher Andy Brunning has put together this nifty infographic on the alchemy of tanning lotion, along with a description of the principle chemical reactions that give people that golden, radiation-free glow.
The main chemical used in tanning lotions is dihydroxyacetone, commonly abbreviated as DHA. In the 1950s, Eva Wittgenstein, a scientist studying the use of DHA orally for children with glycogen defects, observed that spillages of the chemical on the skin led to coloration. Subsequent research culminated with the first tanning lotion being introduced in the 1960s. Those initial formulations, however, left much to be desired (tales still abound of people transformed into hues of orange).
So how does DHA work to induce the appearance of a tan? Brunning explains:
DHA actually acts on the dead skin cells on the surface of our skin. The amino acids in this dead layer of skin can react with DHA in order to produce chemicals called melanoidins. The reaction can be classified as a Maillard reaction – precisely the type of reaction that's responsible for browning in foods such as meat when they're cooked (and a reaction we discussed previously when looking at the compounds that contribute to the smell of bacon). The melanoidins produced by tanning lotions absorb certain wavelengths of light due to their structure, resulting in a visually browning effect on the skin.
The effect of DHA isn't instantaneous. It takes around 2-4 hours for the browning effect to kick in, and it can continue darkening for as much as 72 hours. Because it's the dead cells on the skin's surface that it affects, the tan it induces lasts for up to ten days, fading as these dead skin cells are shed, so reapplication is necessary to maintain the effect.
Tanning lotions, then, may be a convenient shortcut to tanning without the associated risk of sunburn. However, there are a few caveats. Firstly, studies have shown that, after application of tanning lotions, the skins sensitivity to ultraviolet light increases slightly. A 2007 study found that, for 24 hours after a lotion was applied, the amount of UV-induced free radicals produced was 180% higher than untreated skin. Some tanning lotions contain sunscreen to help guard against this, but proper sunscreen should still be applied when using tanning lotions.
In short, there doesn't seem to be too much risk to using fake tan lotions, as long as people remember to protect themselves against the sun while wearing it. Fortunately, studies indicate that many people who use lotions to produce fake tans spend less time sunbathing or in tanning beds—thereby reducing their UV radiation exposure, which is linked to a higher risk of skin cancer.
[Source: Compound Interest]