Capillary malformations (CM) result from an increased number of capillaries (the smallest blood vessels) concentrated in the superficial skin layers, leading to an increase in blood flow in that area of skin. Because the lesions are close to the skin surface, the increased blood flow at the site causes an externally visible red mark or "stain." CMs are present at birth and are often located on the head and neck area, but can appear on any part of the body. Capillary malformations are equally common in males and females, as well as in full-term and premature infants.
Some capillary malformations may indicate the presence of other rare conditions such as Sturge-Weber syndrome, Parkes Weber syndrome, Klippel-Trenaunay syndrome, Proteus syndrome, and macrocephaly-capillary malformation syndrome. CMs that extensively involve the eyelids may be associated with the development of glaucoma.
Recent research suggests that some CMs may be the result of a genetic mutation that occurs shortly after conception. While the exact cause is not completely understood, experts agree that CMs are not caused by anything the mother did during her pregnancy. There are no known ways to prevent this condition.