Chemistry of Fake Tan 2015We’re all well versed in the dangers of spending too much time in the sun. A golden tan after a few weeks away in the sun is everyone’s aspiration, but no-one wants to come back from a holiday red as a cooked lobster, hence the need for sunscreen (which we looked at in a previous post). However, if you’re unlucky enough not to have the time for a couple of weeks on the beach, you might be tempted to resort to tanning lotions to achieve a tanned look. These can induce the appearance of a tan, through the action of the chemicals they contain.

The main chemical used in tanning lotions is dihydroxyacetone, commonly abbreviated to DHA. Tanning lotions can contain up to 15% DHA, though the lotions available to buy in shops max out at 5%, and are usually in the 3-5% range. Obviously, the higher the percentage, the more pronounced the tanning action, though higher percentages tend to be more susceptible to streakiness after application. Another chemical, erythrulose, can also be used, though as its tanning effect is more gradual, it’s more commonly used in conjunction with DHA (if at all).

Although its skin-browning effect was noted by german scientists in the 1920s, DHA’s action on the skin was turned to utilisation for tanning lotions by complete accident in the 1950s. Eva Wittgenstein, a scientist studying the use of DHA orally for children with glycogen defects, noted that spillages of DHA on the skin led to colouration. Research on this aspect culminated with the first tanning lotion being introduced in the 1960s. The first formulations, in fairness, probably still needed a little refining – there are plenty of tales of application leading to bright orange, streaky tans, which probably still colour our perception of fake tanning today.

So how does DHA work to induce the appearance of a tan? 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 skin’s 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.

You might think that, once a tan from tanning lotions has developed, this will afford your skin some natural protection from the sun’s rays. However, normal tanning is a result of the production of melanin in the skin; the melanoidins produced by tanning lotions do not afford the same protection. It’s estimated that a fake tan only affords an SPF of 3 – much too low to offer significant protection against the sun’s rays, so you need to make sure you still slap on the sunscreen!

Whilst DHA is approved for use in lotions, and the tanning effect it produces is non-toxic, its use in spray tanning booths is a little more of a grey area. This is because it’s entirely possible that ingestion or inhalation of DHA could occur during the process. There are no confirmed effects on the body at the concentrations used in tanning lotions or spray tans, but a study using much higher concentrations did find that DNA damage was observed in bacteria cells. However, the relevancy of the findings of this study to any mutagenic activity in humans has been disputed. Other studies have found that some DHA from tanning lotions is absorbed by living skin tissue (as much as 11%), but it’s unclear if this has any effect on the body.

In a slightly odder study, it was found that DHA can cause severe contact dermatitis in Mexican hairless dogs. Quite why someone decided to apply tanning lotion to Mexican hairless dogs isn’t entirely clear, but if you happen to own one… maybe go easy on applying tanning lotion to it?

In short, there doesn’t seem to be too much risk to using tanning lotions, as long as you remember that the tan they generate won’t really offer you any protection from the sun’s rays. With the evidence of increased UV sensitivity, they should definitely be used in combination with sunscreen!

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