How the sun and UV cause cancer

Kids on a sunny beach

Overexposure to ultraviolet (UV) radiation from the sun or sunbeds is the main cause of skin cancer. In the UK more than 8 in 10 cases of melanoma, the most serious type of skin cancer, could be prevented through enjoying the sun safely and avoiding sunburn.

What is UV?

There are 2 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.

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.

Sunbeds give off UVA and UVB, but the mixture of the two is usually different to natural sunlight and the UV is often much stronger.

What is sunburn?

Sunburn is a clear sign that the DNA in your skin cells has been damaged by too much UV radiation. Getting painful sunburn, just once every 2 years, can triple your risk of melanoma skin cancer.

Sunburn doesn’t have to be raw, peeling or blistering. If your skin has gone pink or red in the sun, it’s sunburnt.

Sunburn is caused by 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.

What happens to my skin when it burns?

See what happens to your skin when you get sunburnt.

Sunburn and skin cancer, the burning issue | Cancer Research UK

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

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 sunburn.

The blood vessels around the sunburnt skin 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 sunburnt skin gives off heat – actually, it is 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 sunburn is swollen and painful.

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 damaged cells that could lead to cancer. Although skin peels and new skin layers form, some damage can still remain. So it is important to try to avoid burning in the first place.

What should I do if I get sunburnt?

Getting sunburnt doesn’t mean you will definitely develop skin cancer. But getting sunburnt a lot does mean you have a higher risk of the disease. So if you have had sunburn in the past, it’s a good idea to think about what more you can do to protect your skin next time.

If you notice your skin becoming pink or red, you should come out of the sun and cover up to help stop any more damage from happening. Putting on more sunscreen won’t help and won’t let you safely stay out in the sun for longer.

Can skin cancer spread?

Melanoma and non-melanoma skin cancers can be invasive. As well as growing across the surface of the skin, tumours can sometimes grow down through the layers of skin. If the tumour grows through the wall of a blood or lymph vessel, cancer cells can break off and spread to other parts of the body. This is why skin cancer is usually easier to treat successfully when it is caught at an early stage.

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