Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Moles ?
    ### Response:
    Moles are growths on the skin. They happen when pigment cells in the skin, called melanocytes, grow in clusters. Moles are very common. Most people have between 10 and 40 moles. A person may develop new moles from time to time, usually until about age 40. In older people, they tend to fade away.
    