What Causes Melanoma?

The exact cause of melanoma is not known. A number of factors, however, can increase a person’s chances of developing melanoma, including:

• Fair complexion and blond or red hair - People with light skin are at higher risk than darker-skinned, dark-haired persons. This is because they have lower levels of melanin in their skin. Melanin helps to protect the skin against sun damage and causes it to tan when exposed to the sun.
• Frequent tanning or sunburn - Excessive sun exposure is a major risk factor for all types of skin cancer. Exposure to ultraviolet radiation from the sun or from tanning booths can damage the skin over time and make it more susceptible to skin cancer. People who have had one or more severe, blistering sunburns are at increased risk for melanoma.
• Dysplastic nevi - Abnormal moles called dysplastic nevi are more likely than normal moles to become cancerous. Many people have a few of these abnormal moles. Those who have many dysplastic nevi are at higher risk for developing melanoma. People with a family history of both dysplastic nevi and melanoma are at highest risk for melanoma.
• Many moles - Having many moles increases the risk of developing melanoma.
• History of skin cancer - People who have been diagnosed with any form of skin cancer in the past are at higher risk for developing melanoma.
• Weakened immune system - People whose immune systems have been weakened due to chemotherapy drugs or medical conditions are at increased risk for several types of cancers, including melanoma.
  

Over the past several decades, the incidence of all types of skin cancer has been increasing each year in the United States. Skin cancers were once found much more often in people over age 50, but are now beginning to occur more often among younger people. One reason for this increase is believed to be the increased amount of sun exposure throughout the world, due in part to the popularity of sun tanning outdoors and in tanning salons.

In addition to these risk factors, there are less common, genetic risk factors for melanoma. Approximately 10 percent of people diagnosed with melanoma have a family history of the disease and are therefore at higher risk. At highest risk are members of rare, melanoma-prone families. These families usually have three or more affected members in two or more generations on the same side of the family. These family members often have dozens or hundreds of atypical moles.

A rare, inherited skin condition called xeroderma pigmentosum also increases the risk for melanoma. People with this disorder are extremely sensitive to ultraviolet light because of a genetic defect that prevents the repair of sun-induced damage to DNA. As a result, they have a 1,000 times higher risk of developing skin cancer than people without the disorder. Almost half of people with xeroderma pigmentosum develop some form of skin cancer by the age of 8. The condition shortens life expectancy by more than 30 years.