noun, plural: birthmarks
A mark on the skin that is visible at birth or shortly after birth
Birthmarks are marks on the skin at birth or shortly afterwards. They are an irregularity on the skin caused by an overgrowth of blood vessels, melanocytes, etc. or by dilated capillaries. There are two major types of birthmarks: vascular birthmarks and pigmented birthmarks. Vascular birthmarks are those that arise when blood vessels do not form correctly whereas pigmented birthmarks are those that are associated with a localized overgrowth of melanocytes. Vascular birthmarks are sometimes referred to as red birthmarks because of their lighter hue compared with the pigmented birthmarks. They are exemplified by nevus simplex (salmon patches), hemangiomas, and port-wine stains. Pigmented birthmarks include melanocytic nevus (moles), cafe au lait spots, and mongolian spots. The underlying cause of most birthmarks is still unfounded. Some of the birthmarks are not hereditary, e.g. macular stains, hemangiomas, and port-wine stains.
The term birthmark is sometimes used synonymously with nevus. However, the latter is a more wide-ranging term and birthmarks are only one of the different types of nevi.