Everyone has moles (also known as “nevi”), sometimes 40 or more. They are usually brown in color and can be various sizes and shapes. The brown color is caused by melanocytes, special cells that produce the pigment melanin. Moles probably are determined before a person is born. Most appear during the first 20 years of a person’s life, although some may not appear until later in life. Any rapid or suspicious changes in a mole, including changes in color, shape, symmetry, or size, especially when one mole on an individual looks different than the rest, should prompt immediate evaluation to ensure that it is not evolving into melanoma skin cancer.