Most people get sunburn super easily, it just takes a few minutes sitting in your garden or on a beach, and then a couple days later the skin starts peeling off. It’s seriously pretty gross—not exactly the effect most people go for when they sunbathe.
But, what really happens when you get a sunburn? Most burns occur if you come in contact with something hot, like when you scald the roof of your mouth on a slice of pizza. But sunburns are actually not caused by heat. Sunlight is made up of a bunch of different types of radiation.
One of them is infrared radiation, which is primarily what makes sunlight feel hot. But there’s also visible light, which allows us to see sunlight, and then there’s ultraviolet radiation. Ultraviolet, or UV, radiation is what causes a sunburn. It can wreak havoc on skin cells by disrupting important molecules, like DNA.
So, your body does its best to protect you from it. When UV radiation hits your skin, pigments called melanin absorb it, and shield your DNA from harm. Now, melanin is present in our skin cells all the time—it’s what gives your skin its particular color. It’s created by special cells called melanocytes, which then distribute the melanin to other cells called keratinocytes.
Those are the most common cells in your outermost layer of skin. When your skin is exposed to UV, the melanocytes ramp up their melanin production, and also transfer more melanin to the keratinocytes. This happens to varying degrees based on your genetic makeup, but that’s why your skin might turn darker, or tan, if you’re out in the sun for a while. But, the melanin defense is far from foolproof—regardless of how dark your skin is, or how much you tan, some UV rays can sneak past.
And when they do, they can damage your DNA. This can actually happen in a few different ways. Sometimes the radiation will directly zap your DNA, damaging it in just a trillionth of a second. Alternatively, UV rays can do something more sinister—they can actually turn your melanin against you.
The radiation can make your cells produce these harmful molecules called free radicals. Now, this is a little bit complicated, but essentially the free radicals excite an electron in your melanin. The melanin then bumps into your DNA and excites an electron there—which can cause the DNA to kink. Regardless of how it happens, once your cells are damaged they start producing warning molecules, signalling that something bad is going on.
If enough cells produce the signal, your body will mount an inflammatory response, sending lots of different types of blood cells to the area to stop and repair the damage. And it’s this influx of blood that causes the redness you typically see with a sunburn, depending on how light your skin is. So, what about the peeling? Well, your skin cells are shedding all the time without you noticing it. You actually have stem cells in your skin that live for decades.
The stem cells produce layers of keratinocytes, which fall off and are replaced over time. But those keratinocytes don’t mature properly when they’re damaged by UV. So instead of flaking off inconspicuously, they all clump up and peel off together. Now, your body actually has enzymes that repair a lot of the DNA damage caused by UV rays.
But, it can’t always repair all of it. And if the damage isn’t fixed in one of your stem cells, you might have a real problem. When those cells replicate, they might create a mutation at the site of the damage. And depending on where the mutation occurs, this could lead the cell to become cancerous sometime down the road.
Remember, even if you don’t tend to burn, UV radiation can damage your DNA. So if you know you’re going to be out in the sun for a while, make sure you’re covered up or wearing sunscreen. For most people, being outside and exploring the world is super important for their happiness, and excites their curiosity. But it’s way more fun to go on an outdoor adventure without coming home to disgusting peeling skin.

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