A port-wine stain ("nevus flammeus"), also commonly called a firemark, is a discoloration of the human skin caused by a vascular anomaly (a capillary malformation in the skin).
A port-wine stain ("nevus flammeus"), 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 (a capillary malformation in the skin).