Melanoma is a cancer that usually starts in the skin, either in a mole or in normal-looking skin. About half of all melanomas start in normal-looking skin.
The information in this section is about a skin cancer known as malignant melanoma. We also have information about other types of skin cancer known as non-melanoma skin cancers. These include basal cell carcinoma (rodent ulcer) and squamous cell carcinoma. The number of people developing melanoma is continuing to rise. It is one of the most common cancers in people aged 15–34. Although like most cancers, it’s more common in older people. People with black or brown skin are much less likely than people with white skin to get melanoma. This is because their skin has more natural protection against it. In women, the most common place to develop melanoma is on the legs. In men, it’s on the chest and the back.
About half of all melanomas start with a change in previously normal-looking skin. This usually looks like a dark area or an abnormal new mole. Other melanomas develop from a mole or freckle that you already have.
Risk Factors for Melanoma
A risk factor is something that increases your chance of developing a health condition such as cancer. For example, smoking is the best known risk factor for lung cancer. Having a particular risk factor doesn’t mean you definitely will get cancer, just as people without any known risk factors can develop cancer.
The main risk factor for developing melanoma is exposure to UV radiation. This can be through natural sunlight, or through the artificial light used in sunbeds or sunlamps. UV radiation damages the DNA (genetic material) in our skin cells. This can cause skin cancers such as melanoma.
In the United States, the number of white people developing melanoma and other skin cancers is steadily rising. One of the reasons for this is increased sun exposure during sunny holidays. Increased screening has also led to a rise in the number of very early and thin melanomas being diagnosed.
It’s important to be aware of the damage that too much sun exposure can cause, and to take steps to protect yourself. However, experts recommend regular exposure to a small amount of sunshine. This helps our bodies make vitamin D, which keeps our bones and teeth healthy. It also helps our immune system and has some anti-cancer effects.
The amount of exposure you need depends on your hair and skin type, the time of year and which part of the world you live in. It’s important not to stay out in the sun for long enough to let your skin redden or burn. Episodes of severe sunburn that cause the skin to blister, especially during childhood, can increase the risk of melanoma in the future.
Sunbeds use artificial UV rays that damage the DNA in your skin. They may increase the risk of melanoma. The more you use a sunbed or lamp, and the earlier in life you begin using them, the greater your risk. It’s important not to use sunbeds and to take precautions to protect yourself from too much sun exposure. This is especially important if you’ve had melanoma (or any other type of skin cancer) in the past. It’s also important if you’re at an increased risk of melanoma (see below).
Although exposure to UV radiation from the sun or sunbeds is the main risk factor for developing melanoma, it’s not the only risk factor. Like other cancers, there are many things that may lead to the development of melanoma.
Your skin type
People with fair skin, red or fair hair, blue eyes and freckles are more sensitive to the sun. Because of their skin type, they burn more easily and so are more at risk of getting melanoma. Having naturally dark (brown or black) skin lowers your risk of getting melanoma, but it doesn’t mean that you’ll never get it.
Having lots of moles and unusual moles
People who have a lot of moles (especially over 100) have a higher risk of getting melanoma. So do people with moles that are bigger than average, or that have an irregular shape or color. These moles (sometimes called atypical dysplastic naevi) rarely change into melanoma, but it’s important to check them regularly for changes. Having lots of moles and atypical moles can run in some families. If you were born with a dark, hairy mole or a birthmark over 20cm (congenital naevi) this also increases your risk of melanoma. If you have lots of moles or unusual moles, you can be referred to a skin specialist for advice and an assessment of your skin.
Family history of melanoma
This increases your risk, especially if you have two or more close relatives who’ve had melanoma. Only a small number of melanomas are thought to be caused by inherited genes. Some of these genes may also be linked to pancreatic cancer. This helps explain why some families at risk of melanoma are also at increased risk of pancreatic cancer. People with a family history of melanoma or pancreatic cancer should be referred by their PCP to a family cancer clinic.
People with a weakened immune system have an increased risk of melanoma. This could be due to HIV or taking drugs that suppress the immune system (for example, after an organ transplant).