freckle, a small, brownish, well-circumscribed, stainlike spot on the skin occurring most frequently in red- or sandy-haired individuals. In genetically predisposed individuals who have been exposed to the ultraviolet radiation of sunlight, production of the pigment melanin increases in the pigment cells of the skin (melanocytes); the number of melanocytes does not increase. Freckles do not form on surfaces that have not been exposed to the sun. The freckles usually appear after the age of five and tend to fade somewhat in adults. Apart from avoiding sunlight, there is no known way of preventing them. They may, on occasion, be confused with pigmented nevi.