Some risk factors can be controlled, such as smoking, and some cannot be controlled, such as age and family history. Although risk factors can influence the development of cancer, most do not directly cause cancer. Some people with several risk factors never develop cancer, while others with no known risk factors do.
People with increased numbers of moles or those with unusual moles called dysplastic nevi (flat, large moles that have irregular color and shape) are at higher risk for developing melanoma. About 50 percent of melanoma cases occur in people who have dysplastic nevi. Also, people who have weakened immune systems or those who use certain medications that suppress immune function are at higher risk for developing skin cancer. In addition, people who have had one melanoma are at increased risk for developing additional new melanomas; overall, in the general population, two percent of people who develop one melanoma develop other new melanomas. People who have had a non-melanoma skin cancer are also at a somewhat increased risk for developing melanoma.
Approximately 10 percent of melanoma occurs in individuals who have a family history of melanoma. Therefore it is recommended that close relatives (parents, brothers and sisters, and children) of a person with melanoma routinely have their skin examined. Alterations in two genes that may lead to melanoma have been identified. These genes, however, only account for a small proportion of families with melanoma. Genetic testing for these two genes in not currently used in clinical practice. It is likely that other genes and environmental factors also affect risk of melanoma.
Exposure to Ultraviolet (UV) Radiation
Ultraviolet B (UVB) radiation from the sun produces sunburn and plays a role in the development of both melanoma and non-melanoma skin cancer. Ultraviolet A (UVA) radiation penetrates skin more deeply and may also play a role in the development of both melanoma and non-melanoma skin cancer. People who live in areas with bright sunlight year-round or at high altitudes have a higher risk of developing skin cancer, as do those who spend significant time outside during midday hours. People who use tanning beds, tanning parlors or sun lamps are also at increased risk for skin cancer. Even people who tan well increase their risk of melanoma with more sun exposure.
Less pigment (melanin) in skin offers poorer protection against UV radiation. People with light hair and light-colored eyes who have skin that tans poorly or freckles, or those who burn easily, are two to three times more likely to develop melanoma.
According to many scientific studies, multiple severe or blistering sunburns early in life increase the risk of developing melanoma.