Moles are growths that can form anywhere on the skin and are typically round or oval in shape. They can be solitary or several, rough or smooth, flat or elevated. They develop when the melanocytes—the cells that produce color in the skin—grow in groups rather than uniformly throughout the skin. Moles often measure less than a quarter of an inch. Although some moles may occur later in life, the majority of moles appear before the age of 20.