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How does UV cause skin cancer

Too much UV radiation from the sun or sunbeds can damage the genetic material (the DNA) in your skin cells. If the DNA builds up enough damage over time, it can cause cells to start growing out of control, which can lead to skin cancer.

There are two main types of UV rays that damage our skin. Both types can cause skin cancer:

  • UVB is responsible for the majority of sunburns.
  • UVA penetrates deeper into the skin. It ages the skin, but contributes much less towards sunburn.

Both UVA and UVB can damage DNA in the skin, which can lead to skin cancer. A third type of UV ray, UVC, is the most dangerous of all, but it is completely blocked out by the ozone layer and doesn’t reach the earth's surface.

Your body has ways of repairing most of the damage. But it is not perfect - some damaged DNA can be left behind. Your body's attempt to repair this damage is what causes the painful symptoms of a sunburn. Getting a painful sunburn just once every two years can triple the risk of melanoma. This is why it is important to avoid getting caught out by sunburn.

What is sunburn?

Sunburn is a clear sign that the DNA in your skin cells has been damaged by too much UV radiation. Sunburn doesn’t have to be raw, peeling or blistering. If your skin has gone red in the sun, it’s sunburnt.

Sunburns are caused by ultraviolet radiation (UV) from the sun. You can’t feel UV rays – the heat from the sun comes from infrared rays, which can’t burn you. This is why people can still burn on cool days.

Check out our sunburn animation below to see what happens to your skin when you get sunburnt.

Do I have to worry about sunburn in the UK?

Most people think about sunburn as something that happens on holiday or in hot, sunny places. But in a recent survey more than a third of people admitted the last time they were sunburnt was in the UK. And beware of getting burnt while you’re out and about, rather than deliberately 'sunbathing'. You may be outdoors watching sport, doing the gardening, walking round town or just sitting in the park.

Why are sunburns red, hot or painful?

When UV radiation damages DNA, your body tries to repair the damage. The blood vessels in the local area swell, allowing blood to rush into it. This is why sunburn looks red.

Blood inside your body is also hot, which is why it feels like sunburns give off heat - actually, they are usually no hotter than your core body temperature. The wider blood vessels allow the cells of your immune system to travel to the site of the damage. They also release chemicals which trigger inflammation - this is why bad sunburns are swollen and painful.

Why do sunburns peel?

Sometimes, the sun damages skin cells so severely that they must be destroyed. Peeling after sunburn is your body's way of getting rid of these damaged cells. This is necessary because cells damaged by the sun are at risk of becoming cancerous.

Although skin peels and new skin layers form, some damage can remain. This can build up over time, and increase your risk of skin cancer. So it is important to try to avoid burning in the first place.