If the last blog post got you thinking that sunburns suck, you’re probably not alone. But what happens if you forget your sunscreen and get yourself a real backslapper of a burn? Your know, the kind that makes your not-so-well-meaning friends slap you on the back and ask “Does that hurt?” while trying to keep a straight face. So after you get over the pain of that slap, you may start to wonder…who your friends are. Probably. But you may also wonder what is going on in your skin when you get a bit too much sun.

Okay, now to get down to the science of sunburns. What is really going on in your millions of skin cells when the sun strikes them? The energy that comes from the sun, known as solar radiation, is exactly that, radiation! Radiation is very damaging to the hereditary material, or DNA, in your skin cells. DNA is found in all cells. It is the hereditary material that tells your cells when to make proteins, when to make pigments (color molecules) to make your skin dark like your mom’s or fair like your dad’s, and so forth. The radiation in sunlight can damage this DNA over time. If you are out in the sun for too long without sunscreen, this often happens, especially if you have fair skin.

So far so good, but why does your skin get all red and hot when this damage occurs? Whenever there is damage to cells in your body, a special healing response kicks in. When the cells in the skin are damaged, the body increases the flow of blood to the area. The blood brings special chemicals and cells with it that help heal the cells. When the blood rises to the upper layers of your skin, the skin looks red and hot—in other words, you’ve got a sunburn! Have you ever pressed your skin when you had a sunburn and noticed it went white? And then when you no longer pressed it, it went red again? When you pressed the skin, the blood moved, and the skin went back to white again. When you moved your hand, the blood came back and your skin went red again.

Of course, if you have darker skin, you may rarely, if ever, get a sunburn. This is because your skin has special pigment in it that absorbs the radiation from the sun before it can damage your cells. The darker your skin is, the more of this pigment you have. This is why red hair and freckles is the best invitation for sunburn known on the planet. These people have really pale skin with little pigment. On the other hand, if you have super dark skin, count yourself lucky. You will save a bundle when it comes to sunscreen and you have a much lower chance of getting skin cancer!