We tan because our skin makes a brown pigment called melanin. The surprising part is that the colour doesn't come from the sun painting us brown on the outside. It comes from the inside — from the skin itself. So why does skin tan in the sun? The answer may be the opposite of what you think: a tan is not a sign that the skin is enjoying itself. It is a sign that the skin is defending itself against something we cannot see.
What happens in the skin when we tan?
Melanin is the name of the brown pigment the skin makes when sunlight hits it. Deep inside the skin sit tiny cells that work like little paint workshops. When the UV rays in sunlight reach them, they start making brown grains of melanin — and the more sun, the more grains.
But the melanin doesn't just stay put. The grains move upward and settle like a little roof right over the most important part of each skin cell. Think of a parasol on the beach: it isn't there to look pretty, it's there to give shade. Melanin does exactly the same thing inside your skin — it gives the cells shade from UV light.
Here is the part that flips everything around: your tan is the skin putting up parasols as fast as it can. It turns brown because it has to work, not because it feels good.
Why this matters for children
When children understand that a tan is the skin's defence, sunscreen suddenly makes sense instead of feeling like a chore. It isn't something grown-ups nag about for no reason. It's an extra parasol that helps the skin so it doesn't have to do all the work alone. This isn't about being afraid of the sun — being outside is healthy. It's about understanding what the skin does so we can give it a hand.
Try it at home: a sun print on paper
You can't see UV rays with your eyes. But you can see what they do — if you give them a little time.
You need: a sheet of coloured paper (dark works best), a few flat objects that won't move (keys, scissors, leaves), and a sunny windowsill where the paper can rest undisturbed for a few days.
- Lay the flat objects on the paper so they fully cover some areas.
- Put the sheet in full sun and leave it for a few days.
- Don't move the objects — check each day to see what is happening.
- After a few days, lift the objects away and look.
Where the sun reached the paper, the colour has faded. Where the objects shaded it, the colour is still strong. That fading is the UV rays at work — the very rays your skin protects itself from with melanin. What happens if you leave it another whole week?
Questions to wonder about
- If the skin makes parasols when it gets sun, why do we turn pale again in winter?
- Some people tan quickly and others barely at all — what is different about their skin?
- Animals have fur, feathers or scales but no sunscreen — how does a polar bear, a frog or a fish protect itself from the sun?
Every child is made of good atoms. At Good Atoms, we help them discover it. Explore free content at goodatoms.com.