A port-wine stain, also commonly called a firemark, is almost always a birthmark; in rare cases it can develop in early childhood. It is caused by a vascular anomaly. Port-wine stains are named for their coloration, which is similar in color to port-wine, a fortified red wine from Portugal.
Port-wine stains ordinarily persist throughout life. The area of skin affected grows in proportion to general growth. Port-wine stains occur most often on the face but can appear anywhere on the body, particularly on the neck and upper trunk. Early stains are usually flat and pink in appearance. As the child matures, the color may deepen to a dark red or purplish color. In adulthood, thickening of the lesion or the development of small lumps may occur.