Moles are growths on the skin that are usually brown or black and can appear anywhere on the skin, alone or in groups. They are caused when cells in the skin called melanocytes grow in clusters instead of being spread throughout the skin. Melanocytes are responsible for producing melanin, the natural pigment that gives skin its color. The number of moles a person has is mainly determined by genetics, but exposure to sunlight, especially in childhood and early teenage years, can lead to new moles developing.

Most moles are harmless and do not require treatment. However, if a mole changes in size, shape, or color, or if it starts to itch, bleed, or become painful, it should be evaluated by a dermatologist. Unusual moles that have irregular borders or an asymmetrical shape, or that change in color, shape, size, or height, may indicate melanoma, a type of skin cancer.

In summary, moles are caused by clusters of melanocytes in the skin and are usually harmless. While most moles are not dangerous, changes in a moles appearance or symptoms such as itching, bleeding, or pain should be evaluated by a dermatologist.