Definition of Port-wine stain:

A port-wine stain is birthmark in which swollen blood vessels cause a reddish-purplish discoloration of the skin.

Causes, incidence, and risk factors:

Port-wine stains occur in about 3 out of 1,000 people.

Port-wine stains may be a sign of Sturge-Weber syndrome or Klippel-Trenaunay-Weber syndrome.