Complications

Melanoma is the main complication of moles. Some people have a higher than average risk of their moles becoming cancerous and developing into melanoma. Factors that increase your risk of melanoma include:

• Being born with large moles. These types of moles are called congenital nevi. On an infant, such moles are classified as large if they're more than 2 inches (5 centimeters) in diameter. Even a large mole seldom becomes cancerous and almost never before the child reaches puberty.
• Having unusual moles. Moles that are bigger than a common mole and irregular in shape are known as atypical (dysplastic) nevi. They tend to be hereditary. And they often have dark brown centers and lighter, uneven borders.
• Having many moles. Having more than 50 ordinary moles indicates an increased risk of melanoma. Two studies add to the evidence that the number of your moles predict cancer risk. One showed that people under 50 years old who have 20 or more moles on their arms are at increased risk of melanoma. Another showed a relationship between the number of women's moles and breast cancer risk.
• Having a personal or family history of melanoma. If you've had melanoma before, you are at increased risk of a mole becoming cancerous. In addition, some types of atypical moles lead to a genetic form of melanoma.