Rapid changes in any mole, non-healing sores, or new lumps require medical evaluation to check for melanoma. Nevi have no function. However, they are important because they can sometimes lead to a potentially deadly skin cancer called malignant melanoma. Even more infrequently, melanoma can occur in the brain or spinal cord of those with neurocutaneous melanosis, even after external skin nevi have been removed. NCM has also occured in those with only a few satellite nevi.
Most moles are harmless, but some moles do have a greater chance to develop melanoma.
These include larger moles, very dark moles, and moles with varying colors. Changes in growth, in color, in surface texture, pain, bleeding, or itching are all of concern. Any such changes should be evaluated medically if they last longer than 2 weeks. Pregnancy increases the production of melanin in the body. There is currently no evidence that pregnancy increases the risk of melanoma for women with large nevi.