Skin cancer risks & causes
Risks and causes of melanoma skin cancer
Melanoma skin cancer is the 5th most common cancer overall in the UK. Skin cancer rates are more than 4 times higher than they were in the late 1970’s in Great Britain.
Some of the increase in melanoma may be because doctors are better at watching people for signs of melanoma, and detecting it at an early stage. But it also may be to do with a change in how much time we spend in the sun, such as more people taking holidays abroad.
Your risk of developing cancer depends on many factors, including your age, genetics, and exposure to risk factors.
Having any risk factors does not mean you will definitely develop cancer.
Moles and melanoma
Some of us have more moles than others. The more moles you have on your body, the higher your risk of melanoma. 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.
Also, people with just 1 unusually shaped or very large mole (atypical naevi) have an increased risk of melanoma. The risk increases with the number of atypical naevi.
Birthmarks and melanoma
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 is 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 their whole skin checked every year by a skin specialist (dermatologist).
Ultraviolet light (radiation) is the main environmental factor that increases the risk of developing melanoma.
Ultraviolet light comes from the sun or sunbeds. But some people are more at risk of getting melanoma than others, as this page explains.
Studies show that people with solar keratoses on their head and neck have an increased risk of melanoma on their head, neck or limbs. Solar keratoses are patches of rough, dry skin caused by over exposure to sunlight.
Skin colour and freckling
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 is rare for black people in the UK to get melanoma.
If melanoma occurs in African or Asian people they are mostly a type that occurs 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.
If you have a tendency to get sunburn, you are at more than average risk of melanoma. People most at risk are those who don't tan at all, such as people with very fair skin and those who go red and then peel before getting a tan.
Intermittent sun exposure
In the UK, most people are not exposed to the sun for the whole year. But over the past couple of decades, more and more people have been going abroad for 2 or 3 weeks a year for a holiday and to get a sun tan. The number of people getting melanoma has increased considerably in the UK since it became popular to have a tan and go abroad for holidays.
People who are exposed to strong sunlight every now and then, like holidaying in a hot country, are more at risk of melanoma than people who are very regularly exposed to sunlight, like people who work outdoors.
People with a higher socioeconomic status have a higher risk of melanoma. This is probably because they can afford to take more foreign holidays. But there may be other factors involved. It is also important to be careful during hot spells in the UK.
Research has looked into the link between sunburn and melanoma. Sunburn definitely increases the risk of melanoma.
People who have had sunburn are more than twice as 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 increase in risk of melanoma if they have ever used a sunbed. And the risk is highest for people who use a sunbed before the age of 35.
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.
If you have a close relative who has had melanoma, you are more at risk yourself. This is probably partly because we tend to share the same sort of colouring and skin type as our close relatives.
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. They sometimes have a tendency to become cancerous (malignant). But most atypical moles do not turn into cancer. People with moles like this have a higher than average risk of melanoma.
Researchers have found that the family cancer syndrome - familial atypical multiple mole melanoma syndrome (FAMMM) increases your risk of developing melanoma. People who have FAMMM have more than 50 moles and at least one close relative has been diagnosed with a 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 1 in 10 cases of melanoma (10%) may 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.
The risk of melanoma increases with age. So it is more common in older people. Around half of people diagnosed in the UK with melanoma are aged 65 and over. However, younger people can also develop it and it is now the second most common cancer in adults under the age of 50.
Where you were born
Fair skinned people born in a hot country, for example Australia, have an increased risk of melanoma throughout their life. Their risk is higher than people who went to live in a hot country as a teenager or people with similar skin colouring who live in cooler climates.
Fair skinned people born in a hot country may have exposure to the sun as a baby and young child when the skin is most delicate. This doesn't mean you will definitely get melanoma. It just means you should be aware of taking care of your skin in the sun.
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.
It is very important not to think that using sunscreen allows you to spend longer in the sun. You still have to be careful. Most people don't put enough sunscreen on.
Previous melanoma or other cancers
People who have had a melanoma have an increased risk of getting a second melanoma. Their risk is between 8 to 15 times higher than other people in the population.
People who have had melanoma and also have a parent who has had melanoma have a much greater risk of getting another melanoma. Their risk is 30 times higher than the general population.
People who have had a non-melanoma skin cancer have about 3 times the risk of melanoma as the general population.
People who have melanoma of the eye (ocular melanoma), which is very rare, have double the usual risk of developing a skin melanoma.
Melanoma risk is also slightly higher in people who have had various other cancers. These include
non Hodgkin lymphoma
kidney cancer (renal cell carcinoma)
certain childhood cancers
The increase in risk may be because the cancer types share genetic or environmental risk factors.
Other medical conditions
Some studies have shown an increased risk of melanoma for people with Parkinson's disease. More research is needed to understand why this is.
Researchers have found that people with inflammatory bowel disease (Crohn’s disease and ulcerative colitis) have an increased risk of melanoma. Treatment for these bowel conditions may 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.
A meta analysis, which looks at the results of a number of studies together, looked at the link between a condition called sarcoidosis and cancer. The researchers found that people with sarcoidosis have a higher risk of skin cancer than people who do not have this condition.
It is not clear at the moment how the following skin conditions affect melanoma risk:
a type of eczema called atopic dermatitis
One study has shown that people who have asthma may have a slightly lower risk of melanoma.
Studies have shown that people with reduced immunity are more likely to develop melanoma. People may have reduced immunity due to infection with HIV or AIDS or medicines given to suppress the immune system after an organ transplant.
Some studies show an increased risk of melanoma in men who have a higher body mass index (BMI). The same has not been shown for 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 may 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.
Because more women than men get melanoma, researchers have been very interested in whether hormones had a part to play. There has been a lot of research into this area, looking at:
the role of female sex hormones
the pill and hormone replacement therapy (HRT)
There is no conclusive evidence that risk of melanoma is affected by any of these factors. Some women have a natural darkening of the skin during pregnancy. This may make moles show up more clearly. But it is not true that moles are more likely to become cancerous during pregnancy. There is also no evidence that pregnant women diagnosed with melanoma do worse than non pregnant women. If you are worried about this, talk to your GP.
Web content: Cancer Research UK, Accessed Oct 2019.