Risks and causes of melanoma
Your risk of developing melanoma depends on many things including lifestyle factors and some medical conditions. In the UK, around 85 out of 100 melanomas (around 85%) are caused by too much ultraviolet radiation.
Melanoma skin cancer is the 5th most common cancer overall in the UK. The number of people diagnosed with melanoma has increased over the last few decades.
Anything that can increase your risk of cancer is called a risk factor. Those that lower the risk are called protective factors.
Having one or more risk factors doesn’t mean that you will definitely get melanoma.
The risk of melanoma increases with age. So it's more common in older people. In the UK, more than 25 out of 100 people (more than 25%) diagnosed with melanoma are aged 75 and over. But, younger people can also develop it. Compared to most other cancer types, it's also quite common in younger people.
Ultraviolet light (radiation) is the main environmental factor that increases the risk of developing melanoma. Ultraviolet light comes from the sun or sunbeds. In the UK, around 85 out of 100 melanomas (around 85%) are caused by too much ultraviolet radiation.
Intermittent sun exposure
Some people are exposed to strong sunlight every now and then, like holidaying in a hot country. They are more at risk of melanoma than people who are very regularly exposed to sunlight, like people who work outdoors.
In the UK, most people are not exposed to the sun for the whole year. But the number of people getting melanoma has increased considerably in the UK since it became popular to holiday abroad for a few weeks each year and get a sun tan.
It is also important to be careful during hot spells in the UK.
Sunburn increases the risk of melanoma.
People who have had sunburn are more likely to get melanoma than those who have not. The risk is higher if you have had sunburn several times in your life. This increase in risk is seen with sunburn at all ages, not just in childhood.
Research shows that the type of ultraviolet light used in sunbeds (UVA) can cause all types of skin cancer. The International Agency for Research into Cancer (IARC) has classified using sunbeds as a cause of melanoma.
People have an increased risk of melanoma if they've ever used a sunbed. And the risk is highest for people who use a sunbed before the age of 35. Sunbed use by under-18s is banned in Scotland, England and Wales, and Northern Ireland.
Using a sunbed to get a tan before you go on holiday can also increase the risk of melanoma. There is no such thing as a safe tan.
It is difficult to study how sunscreen affects the risk of melanoma. This is partly because people who use sunscreen may stay longer in the sun because they think they are protected. So they actually get more exposure to ultraviolet light overall.
The best way to enjoy the sun safely and protect your skin is to use a combination of shade, clothing (including sunglasses) and sunscreen.
Shade and clothing are more effective than sunscreen at protecting your skin. Sunscreens shouldn’t be used to spend longer in the sun, but they can be useful for protecting the parts of skin not covered by clothing or shade.
Skin colour and freckling
Your skin type and colour affect your risk of developing melanoma. If you tend to burn in the sun, you're more at risk.
People who are very fair skinned, especially with fair or red hair, are more at risk of developing melanoma. So are people with a lot of freckles. People with darker skins can still get melanoma but they have more natural protection against it.
It's rare for black people in the UK to get melanoma. If African or Asian people do get melanoma, it's most often a type of melanoma that develops on the soles of the feet or the palms of the hands (acral lentiginous melanoma). This type of melanoma can also grow under the nail.
The more moles you have on your body, the higher your risk of melanoma. One study found that melanoma risk was higher in people with more than 100 common moles, compared with people with fewer than 15 moles.
This doesn't mean you will definitely get melanoma if you have lots of moles. But it does mean you should be very careful about exposing yourself to the sun. And you should keep an eye on all your moles.
People who have lots of unusually shaped or large moles (atypical mole syndrome) have a higher risk of melanoma than the general population. A large mole is one greater than 5mm in diameter.
Birthmarks are coloured marks on the skin and there are many different types. Different types of birthmarks are made up of different types of cells.
Most birthmarks, such as the common port wine stains and strawberry marks, carry no risk of developing into a cancer. But a very rare type, called a giant congenital melanocytic naevus, can develop into a melanoma if it is larger than 20cm.
Doctors recommend that you check all birthmarks regularly for any signs of change. But they recommend removing large congenital birthmarks at an early age if possible.
If it's not possible to remove the birthmark, it needs to be checked regularly. UK guidelines recommend that people who have large congenital melanocytic naevi should have regular checks by a skin specialist (dermatologist).
Family history and genetic factors
Your risk of melanoma is higher if you have a close relative who has had melanoma. This is probably partly because we tend to share the same sort of colouring and skin type as our close relatives.
Your risk is highest if:
- your relative had melanoma when they were younger than 30
- more than one first degree relative (brother, sister, mother, father, child) have had melanoma
Some families tend to have large numbers of moles, or moles that are unusual (atypical moles). The atypical moles tend to be an irregular shape or colour and may be larger than usual.
An inherited condition called familial atypical multiple mole melanoma syndrome (FAMMM) increases your risk of getting melanoma.
People with FAMMM have:
- many moles, some of which are unusual (atypical) and often different sizes
- at least one close relative who's had melanoma (a close relative is a parent, brother, sister, child, aunt, uncle or grandparent)
Some families with FAMMM are also at a higher risk of developing pancreatic cancer.
Scientists think that around 10 out of 100 cases of melanoma (10%) might be linked to inherited faulty genes. A gene called CDKN2A is known to cause FAMMM. For the small number of families who carry these genes, sun protection is even more important.
Other medical conditions
Research has shown that some medical conditions increase your risk of getting melanoma.
Inflammatory bowel disease (IBD)
Inflammatory bowel disease includes illnesses like Crohn’s disease and ulcerative colitis. The risk of melanoma skin cancer is higher in people with these diseases.
Treatment for inflammatory bowel disease might include drugs that suppress the immune system, which we know can increase the risk of some cancers. But the research shows an increase in melanoma risk even when people have not taken these drugs.
Weakened immune system
Your immune system protects the body against illness and infection. Studies have shown that people with weakened immunity are more likely to develop melanoma.
You might have a weakened immune system due to:
- HIV or AIDS infection
- medicines to suppress the immune system (immunosuppressants) - for example, after an organ transplant
Some studies show an increased risk of melanoma in men with a higher body mass index (BMI). This wasn't seen in women.
But any study looking at the risk factors for melanoma needs to take into account how much time the people have spent in the sun. It might be that women with a larger body mass index have less sun exposure than women with a lower body mass index. So this could be why their risk is lower.
Other possible causes
Stories about potential causes are often in the media and it isn’t always clear which ideas are supported by evidence. There might be things you have heard of that we haven’t included here. This is because either there is no evidence about them or it is less clear.