Moles (nevi) are a common type of skin growth. They often appear as small, dark brown spots and are caused by clusters of pigment-forming cells (melanocytes). Most people have 10 to 40 moles that appear during childhood and adolescence and may change in appearance or fade over time.

Most moles are harmless. Rarely, they become cancerous. Being aware of changes in your moles and other pigmented patches is important to detecting skin cancer, especially malignant melanoma.

More Info: www.mayoclinic.org