Vascular birthmarks are common, idiopathic (of unknown cause) clusters of blood vessel growths found in infants and children. They are present at birth but may not have a noticeable appearance for weeks and sometimes years.

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​These birthmarks are classified in two groups: tumors and malformations. Vascular tumors are neoplasms, involving cellular proliferation of vessels. Vascular malformations, on the other hand, do not involve active proliferation of the blood vessels and are stable throughout one’s lifetime; they are further classified according to the type of vessels found in the birthmark.