Where do sunburns come from?

Vintage Sunburn Ads (1)

Last Monday, I reached over the stove while I was cooking and bumped my wrist against a hot saucepan, sustaining a semicircular blister burn. That Saturday, when my thermal burn was nearly healed, I went to Knoxville Pridefest in a sleeveless blouse and got a sunburn on my shoulders. As I write this, my week-old sunburn is shedding little pieces of skin onto the inside of my T-shirt.

These annoying but altogether normal experiences had me wondering: why do sunburns and thermal burns look and feel so different? Why did my thermal burn heal without peeling everywhere? Why do thermal burns hurt immediately, while sunburns glow warmly but painlessly for hours before you really feel them? And why does one increase the risk of skin cancer while the other does not?

As it happens, science has the answer! Well, science still has to work out the minute details, but on the basic level it has the answer.

When sunburn occurs, ultraviolet radiation penetrates the nuclei of the skin cells and mutates the DNA within. The mutant DNA gets transcribed into mutant bits of non-coding microRNA, which disseminates and triggers an inflammatory response. This inflammation is what makes the sunburn red and warm. If the mutations are pronounced enough, the cells in the first layer of skin will die and eventually peel off. The body has processes that stop the crazy sunburn mutations from spreading, but every time you get a sunburn it increases the statistical possibility that mutations will stick around – and that’s why sunburns increase the risk of skin cancer.

So sunburns are caused by DNA mutations from radiation. Real life is so much less glamorous than superhero comics.

A thermal burn from a hot stove, by contrast, happens when excessive heat melts the proteins inside the skin, causing it to break down. You feel this immediately, which is a good thing when you think about what would happen if you just left your hand sitting on a hot saucepan. Thermal burns have nothing to do with skin cancer because they do not mutate DNA.

It just goes to show that even common experiences can be an opportunity to learn some fascinating science – or, if you’re really smart, to come up with some fascinating science.

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