All moles are medically known as melanocytic nevi (singular: nevus). Colloquially, they are referred to as moles, birthmarks or beauty marks. However, the term “birthmarks” can also refer to vascular red marks, as well as pigment deformities. When moles are present from birth, they are called “congenital moles,” or “congenital nevus.” When they develop later in life (usually before age 40), they are called “acquired moles,” or “acquired nevus.” The term “melanocytic” means that the pigments found in your mole come from your skin’s melanocytes, which produce melanin (i.e. pigment). Moles are the result of overactive melanocytes in your skin. We describe how melanocytes work on our page about hyperpigmentation, which we encourage you to read, here. The concept is almost the same as when a person forms brown, flat marks on the skin. However, pigmentation that results in freckles, port wine stains or melasma is not nearly as advanced as melanocyte clusters that have formed into moles. Adults can have between 10 and 40 harmless moles on their body. Some people are simply born with a condition that makes them prone to developing moles. When there are many, many brown spots on the skin, a person can have dysplastic nevus syndrome, also known as atypical multiple mole-melanoma (FAMMM) syndrome. Dysplastic nevi (irregular-shaped moles) are more likely to become skin cancer than other types of moles. If you have them, you should be checked by a doctor regularly. UV exposure (such as from the sun, or tanning beds) can also put you at risk for moles. These can fall under categorizations of sun damage, which we explain in detail, here. When moles are from sun damage, they are typically called “lentigo,” or “lentigines.” If you have a pre-existing tendency to form moles, you may be at greater risk of developing melanoma (i.e. skin cancer) from UV exposure. You should be extra careful about being in the sun, and you should not tan. When moles turn into cancer, they can become squamous cell carcinoma, basal cell carcinoma, and melanoma. Sometimes, moles can go away on their own. Most of the time, this is not an issue. However, when a cancerous mole disappears, there is cause for concern. It can indicate the cancer has spread to other areas of the body. For that reason, you should regularly be checked for suspicious moles. The best way to prevent moles - whether or not you are genetically predisposed to them - is to stay out of the sun, and use a strong, broad-spectrum sunscreen (even on cloudy days). This ‘rule’ is especially important between 10 a.m. and 4 p.m., when the sun’s rays are at their strongest. Never use tanning beds, either. Please see more on our website.