Freckle: A flat circular spot on the skin about the size of the head of a nail that develops after repeated exposure to sunlight, particularly in someone of fair complexion. Freckles may be yellow, tan, light-brown, brown, or black. They are always darker than the skin around them since they are due to deposits of the dark melanin, a dark pigment.
There are two basic types of freckles -- ephelides and lentigines. Ephelides (singular: ephelis) are flat light-brown spots that typically appear during the sunny months and fade in the winter. Lentigines (singular: lentigo) are small tan, brown, or black spots which tend to be darker than an ephelis-type freckle and which do not fade in the winter.
The sun is not the only factor that induces freckles. Heredity also influences freckling, as witnessed by the striking similarity in the total number of freckles on identical twins. Such similarities are considerably less marked in fraternal twins. A gene for freckles has been mapped to chromosome 4q32-q34.
Freckles are harmless. They may sometimes be confused with more serious skin problems. Conversely, more serious problems such as skin cancer may at times be passed over as a mere freckle. Anyone who has one or more pigmented spots of which they are not certain should be seen by a dermatologist. Treatments are available to lighten or eliminate those freckles whose appearance bothers their owners.