Port wine stain is another birthmark of the vascular nature. It can come up on any area of the skin, but usually affects only one side of the body, and the face and upper trunk are the most common sites. It is due to the blood vessels being kept open abnormally and this shows up as a permanent blush in pink, red, or purple.

Initially it is flat, smooth and pink, but later in life it becomes darker in colour, raised and even bumpy, and bleeds easily.

Mostly they do not cause any discomfort. Port wine stain near the eyelids may lead to increased pressure inside the eyeball, and increased incidence of seizures. When it is extensive on a limb, the growth of that limb may be more than the rest of the body. Unlike strawberry naevus, port wine stain persists through out life and enlarges together as the body grows in size.

It can be cosmetically embarrassing when it appears on the face. Camouflage creams are often very helpful in hiding the disfigurement. Active treatment with pulsed dye lasers can be effective, but it usually requires multiple treatments, and may not clear completely. Depending on the size and site, responses can be quite different. Port wine stains on the limbs respond less well than those on the face. Treatment is more successful when given early in life, before the birthmark becomes thickened.