Every year, millions of us flock to warmer climates in search of sun, sea and relaxation. There’s no better feeling than lounging on a deck chair, soaking in those rays, and letting our solar friend top up that tan. But have you ever wondered how we tan, and why? To answer this, we need to start with the big ball of gas in the sky:
The sun is a thermonuclear fusion reactor – it outputs the same amount of energy in a single second, that the human race would use up in around a million years! Luckily, only around one one-billionth of that energy actually hits the earth, which is why we’re not being cooked alive.
When that energy eventually reaches us, around 10% of it arrives in the form of ultraviolet radiation. You might think this is the light and heat you can see and feel on a sunny day, but that’s actually a misconception – UV light is undetectable to humans. Couple this with the fact that UV light can penetrate our skin and damage our DNA, and you can see why it’s so dangerous.
Luckily, our body has a natural defence to UV light, in the form of melanin, which is a naturally occurring group of pigments in our skin. All of us have melanin, and it’s what that gives our skin its colour – people who have dark skin have more melanin, whereas people who have light skin have less.
When our body detects damage from UV radiation, cells deep within our skin, known as melanocytes, generate melanin and push it towards the surface. This then darkens the outer layer of the skin, which allows it to absorb UV energy and transform it into heat, preventing it from penetrating our DNA.
This darkening becomes visible a few hours after UV exposure, which is why your tan always seems to emerge during the evenings! Once you’re back home from your holiday, your skin gradually replenishes itself with cells containing less melanin, which is why your tan fades away.
Don’t forget though – your body can’t do all the work! So, the next time you’re sipping a cocktail under a clear sky, remember those sneaky UV rays, and give your skin a helping hand with some sun cream.