Any mark, spot, or bump that is present in or around the time of birth on the skin of an infant is a birthmark.
Birthmarks can be categorized according to their composition. Marks as a result of excessive accumulations of melanin are called pigmented birthmarks, since the great majority of them are brown to black. Other birthmarks appear lighter than the rest of the skin due to a relative lack of melanin.
Some birthmarks are composed of blood vessels and are called vascular birthmarks. They are generally red, blue, or purple. Other birthmarks are composed of lymphatic tissue (cystic hygroma), breast tissue, and epidermal tissue, which are often yellow to flesh-colored.
Most birthmarks are probably due to defective migration of cells during fetal development. Once these cells start to multiply, they produce tissue with the characteristics of their cell type though they are not where those cells typically are located.
The treatment of birthmarks depends on the nature of the tissue involved. Generally, measures that destroy the involved cells of the birthmark are required for both pigmented or vascular birthmarks. Either scalpel surgery, lasers, and rarely radiation can be helpful.