Birthmarks are benign (noncancerous) skin growths composed of rapidly growing or poorly formed blood vessels or lymph vessels. Found at birth (congenital) or developing later in life (acquired) anywhere on the body, they range from faint spots to dark swellings covering wide areas.

Skin angiomas are composed of either blood vessels (hemangiomas) or lymph vessels (lymphangiomas)that lie beneath the skin's surface. Hemangiomas (strawberry marks) are found on the face and neck (60%), trunk (25%), or the arms and legs (15%). Congenital strawberry marks, 90% of which appear at birth or within the first month of life, grow quickly, and disappear over time. Lymphangiomas are skin bumps caused by enlarged lymph vessels anywhere on the body.

Vascular malformations are poorly formed blood or lymph vessels that appear at birth or later in life. One type, the salmon patch a pink mark composed of dilated capillaries (tiny blood vessels), is found on the...