What is a port wine stain?

A port wine stain (naevus flammeus) is a red or purple birthmark which affects about 3 out of every 1000 babies. It is a type of blood vessel birthmark which presents at birth as a uniform flat red, purple or pink mark on the skin, often on one side of the body, usually the face. They are congenital overgrowths of small blood vessels in the skin. Port wine stains are twice as common in girls as boys, and they may darken with age, thicken with raised bumps (papules) or ridges and increase in size proportionally to the child's growth. They grow with the individual and do not improve over time. They can occur on any part of the skin surface but cause most concern when they affect the face.