What are large, flat, reddish-purple birthmarks called?

Large, flat, reddish-purple birthmarks are known as port-wine stains. These birthmarks are a type of vascular malformation caused by an overabundance of capillaries just beneath the surface of the skin. Port-wine stains can vary in size and typically do not fade over time; they may change slightly in texture, but their color generally remains stable.

In contrast to hemangiomas, which are raised and can be red or purple and often fade without treatment, port-wine stains remain throughout a person's life and can be associated with certain syndromes if they occur in specific areas, such as the face. Strawberry marks, or infantile hemangiomas, are also raised and may resemble strawberries, while Mongolian spots are blue-grey pigmented lesions commonly found on the lower back or buttocks of newborns, unrelated to the reddish-purple appearance of port-wine stains.