Skin cells develop in a controlled and orderly manner. The new cells push the old ones to the skin surface where they die and are eliminated from the body. When some cells acquire DNA damage, uncontrolled growth of new cells can be triggered, resulting in this skin cancer.

Most of the time, the genetic changes associated with melanoma are acquired during life and are not passed on (not inherited). In some cases, they occur randomly in a cell, with no clear cause, and in others, they are likely to occur as a result of an external cause. It is therefore likely that a combination of environmental and genetic factors leads to the development of melanoma.

Ultraviolet (UV) rays, especially type B but also type A, are a major cause of melanoma as they can damage the DNA of skin cells. However, UV light does not cause all melanomas, especially those that occur on parts of the body not exposed to sunlight, so other factors can influence the risk of melanoma.

The following factors can increase a person's risk of developing melanoma:

Sun exposure: living at high altitudes or in areas with intense sunlight year-round are at increased risk, as well as staying outdoors during midday extended periods.
Indoor tanning in sunbeds, tanning salons, or sunlamps. Their use is strongly discouraged.
Moles: people with many moles or unusual, large moles with irregular shape and color (dysplastic nevi or atypical moles) are at increased risk.
Fair skin: people with fair complexion, blond or colored hair, blue eyes, and freckles have a higher risk of developing melanoma. This risk is also higher in people who tend to burn their skin rather than tan.
Previous skin cancer. People who have already had melanoma or basal cell or squamous cell skin cancer have a higher risk of developing melanoma.
Ethnicity: While it can develop in individuals of any ethnicity, people of Caucasian descent are 20 times more at risk than those of African descent.
Age: it occurs in young adults more frequently than many other cancers. The median age of diagnosis is around 50 years.
Weakened immune system: Both disease and immunosuppressive treatments increase the risk of developing skin cancer, including melanoma.

Additionally, and less frequently, it is possible to inherit genetic changes from parents that increase the risk of melanoma. About 10% of people with melanoma have a family history of the disease, the risk of developing melanoma is 2 to 3 times higher than the average risk if there is a close relative affected. This risk increases if several family members living in different places have been diagnosed with melanoma. In addition, hereditary familial forms of melanoma due to changes in specific genes such as CDKN2A, CDK4, P53, and MITF have been described, although they are rare. Other hereditary conditions (Xeroderma Pigmentosa, Li-Fraumeni syndrome, or hereditary breast and ovarian cancer, among others) are also associated with an increased risk of melanoma.

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