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A risk factor is something that increases the risk of developing cancer. It could be a behaviour, substance or condition. Most cancers are the result of many risk factors. Exposure to ultraviolet radiation (UVR) from the sun, tanning beds or sun lamps is the most important risk factor for melanoma.
Melanoma is being diagnosed more often in both men and women. In Canada, melanoma is slightly more common in men than in women. Older people have a greater risk of developing melanoma, but it is also found in younger people.
Risk factors are generally listed in order from most to least important. But in most cases, it is impossible to rank them with absolute certainty.
There is convincing evidence that the following factors increase your risk for melanoma.
Exposure to ultraviolet radiation (UVR) is the most important risk factor for developing all types of skin cancer.
The sun is the main source of UVR. Most cases of melanoma are caused by exposure to UVR from the sun. It could be from on and off exposure to the sun over your lifetime or exposure to the sun early in your life.
Indoor tanning equipment is also a source of UVR. This equipment includes tanning beds and sun lamps. Exposure to UVR from indoor tanning equipment can cause melanoma.
Having a tan means that your skin has been damaged by exposure to UVR. UVR can cause sunburns, premature aging, melanoma, squamous cell carcinoma (SCC) and cataracts.
Find out more about ultraviolet radiation.
A mole, or melanocytic nevus, is a non-cancerous mark or area of abnormal tissue on the skin. Moles occur when melanocytes grow together in a group. Melanocytes are cells that make melanin, which gives colour to your skin, hair and eyes. Babies aren’t usually born with moles. Moles often begin to appear when you are a child.
Most moles are harmless. But if you have many moles you have a higher risk of developing melanoma.
An atypical mole is also known as a dysplastic nevus. Atypical moles look different from normal moles. They tend to be larger than 6 mm, while normal moles are usually smaller than 6 mm. Atypical moles have an irregular shape with undefined borders, but a normal mole is usually round. Atypical moles often have different colours in them, which can range from pink to dark brown.
Atypical moles can look like a melanoma, but they are not cancerous. Having atypical moles increases your risk of developing melanoma. This risk increases with the number of atypical moles you have.
Congenital melanocytic nevi are birthmarks, or large moles, that are present at birth or develop shortly after. They may be classified as small (less than 1.5 cm), medium (1.5–19.9 cm) or large (greater than 5% body surface area in preteens or greater than 20 cm in teens or adults).
The larger the congenital melanocytic nevus, the greater the risk of developing melanoma.
FAMMM syndrome is an inherited condition. People with FAMMM have many moles (more than 50). They also have one or more first- or second-degree relatives with melanoma. First-degree relatives include your father, mother, brother, sister or child. Second-degree relatives include your aunts, uncles, grandparents, grandchildren, nieces, nephews or half-siblings.
People with FAMMM have a very high risk of developing melanoma.
People with fair or light-coloured skin have a higher risk of developing melanoma than people with other skin types. People with blonde or red hair and blue, green or grey eyes also have a higher risk of developing melanoma. Their risk is greater because people with these features have less melanin. Melanin is what gives colour to your skin, hair and eyes. Experts think that it also helps protect the skin from UVR.
People with a fair or light-coloured skin who had very bad sunburns at an early age have the highest risk for melanoma. People with dark (brown or black) skin have a lower risk of developing melanoma, although it is possible. People with dark skin may be more likely to develop a rare type of melanoma called acral lentiginous melanoma. This type of melanoma occurs on areas not exposed to the sun, such as the soles of the feet or palms of the hands.
Find out more about health effects of UVR exposure and how it affects people with different skin types.
People who have already had melanoma have a higher risk of developing another primary melanoma. Having had basal cell carcinoma (BCC) or squamous cell carcinoma (SCC) is also linked with a higher risk of developing another skin cancer, including melanoma.
Your risk of developing melanoma increases if one or more of your first-degree relatives has been diagnosed with melanoma. First-degree relatives include your father, mother, brother, sister or child. This may be due to family members having similar skin colour and sun exposure habits. It can also be due to similar genetic mutations, although this is rare.
Sometimes genes can change, or mutate, so they increase the risk of cancer. These mutated genes can be passed down from parents to their children. If several family members have the same type of cancer, or if family members have related types of cancer, they might share an inherited gene mutation.
About 5%–25% of families with a higher risk for melanoma have an inherited gene mutation in the CDKN2A gene. This gene is normally a suppressor gene, which means it helps control the growth of cancer cells. When there is a CDKN2A gene mutation, cancer may develop.
Find out more about inherited cancer risk.
People with a weakened immune system have a higher risk of developing melanoma. The immune system can be weakened by certain diseases. It can also be weakened by drugs that people need to take to suppress their immune system following an organ transplant.
People who have had at least one blistering sunburn as a child or teenager have a higher risk of developing melanoma later in life. The more sunburns you have had, the greater the risk of melanoma.
The following inherited conditions can increase the risk of developing melanoma.
Xeroderma pigmentosum (XP) is a rare inherited condition that affects the skin so it can’t repair sun damage. When someone has XP, their skin is more sensitive to UVR so that it changes colour and ages prematurely. People with XP also have a high risk of developing both melanoma and non-melanoma skin cancer.
Werner syndrome is a rare inherited condition that causes the skin to age prematurely. Werner syndrome is most common in people of Japanese ancestry. People with this condition have a higher risk of developing melanoma.
The following factors have been linked with melanoma, but there is not enough evidence to show they are known risk factors. Further study is needed to clarify the role of these factors for melanoma.
The MC1R gene is linked with pigmentation. Certain variations of the MC1R gene determine red hair and fair skin. People with an MC1R variant that causes red hair and fair skin may have a higher risk of developing melanoma.
People who have had radiation therapy in the past or who were exposed to nuclear fallout are likely to have a higher risk of developing melanoma. Some research has also shown that some people who work with ionizing radiation, such as radiation technologists, have higher rates of melanoma.
PCBs are chemicals that were used in many different industries. For example, they were used in electric appliances and plastics manufacturing. PCBs were banned in 1979 because of their harmful effects on people and the environment. A number of studies have suggested that occupational exposure to PCBs likely increases the risk of melanoma, but more research is needed.
PUVA is a common treatment for skin conditions like psoriasis. It uses the drug psoralen and ultraviolet A (UVA) radiation. Psoralen makes the skin more sensitive to UVA light. Receiving PUVA therapy for a long period of time may increase your risk of developing melanoma.
Research has shown that people who are tall may have a slightly higher risk of melanoma.
It isn’t known whether or not the following factors are linked with melanoma. It may be that researchers can’t show a definite link or that studies have had different results. Further study is needed to see if the following are risk factors for melanoma: