It’s that time of year, the clocks have gone back, the days are darker, and skin doesn’t see any real sunlight anymore; in fact personally I’ve been so cold lately that most of my skin hasn’t seen much that isn’t the inside of my new chunky knit jumper and super fluffy slippers for over a fortnight at this point.
And this brings me to a question that I ponder every year; while many people are asking themselves if it’s time to get the fake tan bottle out, I’m nerdily staring at all the fake tan in the supermarket and wondering how does it actually work? It obviously doesn’t simply cover your skin like a coat of paint; otherwise it would wash straight off, so it must actually do something to temporarily chemically change the colour of your skin, surely? It’s intriguing.
Well this year is the year that I stop staring at tanned strangers in the street with a perplexed look on my face. I have discovered how fake tan works… and it’s REALLY COOL. Now instead of staring at tanned strangers, I can tell them how their fake tan actually works. I’m fairly sure that’ll make me seem loads more normal and friendly, yes?
So. Your skin is made up of different layers of cells, and the outermost layer, the one that faces the world every day, is the stratum corneum. The stratum corneum is made up of dead skin cells that migrate from the layers below. This layer of protective cells is your body’s first barrier against the outside world; it protects the living skin cells underneath. One of the key components of the stratum corneum is the keratin protein. Keratin gives the stratum corneum its structure; it is the molecular scaffolding of your skin.
The active ingredient of most fake-tanning products is dihydroxyacetone (DHA). DHA, when applied to skin, reacts with the amino acids, the individual units that make up the keratin protein scaffold. This reaction is known as the Maillard reaction, and it’s weirdly very similar to the reaction that causes bread to brown in the oven. The term fake bake has literally never been more applicable, although obviously fake tan doesn’t require you to actually cook yourself. Luckily.
The fake-bake reaction is as follows: DHA reacts with the amino group (NH2) of an amino acid in keratin to produce water and N-glycosylamine. Glycosylamine, sadly, is a highly neurotic and unstable chemical, and, upon being formed, instantly panics, has an identity crisis and rearranges itself into a ketosamine instead. The ketosamines can then react further to become melanoidins, which pigment your skin. This reaction takes a little time, which is why fake tan darkens in the hours after you apply it, the DHA has to infiltrate your skin and locate the keratin scaffold to start reacting. And, of course, the more DHA you apply, the darker you will go, as more DHA means that more amino groups can produce melanoidins.
Over the course of the next few days, your skin gradually continues to replace the dead cells in the stratum corneum with new dead cells that migrate from the layer below. As this happens, the cells that contain the melanoidins produced by the DHA reaction are naturally shed, and your skin returns to its original lighter colour.
And that’s how fake tan works. It might just be me but I think that’s really pretty cool; and since it only affects the stratum corneum, the layer of dead cells at the surface of your skin, no lasting damage is caused, unlike when UV rays cause your skin to tan, which is even better!