Vitiligo: A condition in which the skin turns white due to the loss of pigment from the melanocytes, cells that produce the pigment melanin that gives the skin color. In vitiligo, the melanocytes are destroyed, leaving depigmented patches of skin. The hair that grows in areas affected by vitiligo may also turn white. The skin is not otherwise damaged. People with vitiligo must protect their skin from exposure to the sun. Also known as piebald skin and acquired leukoderma.