Birthmarks refer to a change in the skin that is present at birth (or becomes evident shortly thereafter). They are created by tissues forming while the fetus is developing in the uterus of the mother, and are remnants of blood vessels, lymphatics, mole cells, hair follicles, oil glands and other cells. Birthmarks are popularly explained by folk lore and superstition but are purely lesions of cellular biology. Most are small, although some are large and can disfiguring. Some birthmarks disappear or fade as the child ages. Consequently, barring some other compelling reason (not just grandmother's desire to have it gone), none should be treated until about age five. Lesions are treated by surgical excision, skin grafts, irradiation, lasers or other modalities, but scarring is common and therapeutic experience and good judgment is required.