Birthmarks are so-called because they are present at birth or appear within the first year of baby’s life. There are two types of birthmark, red birthmarks and pigmented birthmarks, and more than 10% of babies are born with one. They are usually harmless and do not require any treatment.
Red birthmarks, often referred to as port wine stains, are caused by an overgrowth of blood vessels or because capillaries are excessively dilated (open) at the skin surface. It is not known for sure what causes this to happen but they are not inherited from parents or caused by factors during pregnancy. They are probably due to a slight imbalance that causes more of the cells that make the lining of a blood vessel to be made than are needed.
Sometimes, treatment is required if the location of the birthmark has potential health implications. For example, if it is covering the eyes and preventing the individual from seeing properly. Otherwise, birthmarks are a factor of a unique childhood and in some cultures it is even considered good luck to touch someone with a birthmark!