Birth marks are pigment spots or areas, often raised above the skin surface. The most common birthmark is the naevus, or large port-wine stain, which is a mass of dilated blood-vessels often located on the face. Small naevus of a reddish or bluish colour are more common elsewhere on the body. Naevus which are darker and hairy are often called moles.
There are two categories of vascular birthmarks. These are hemangiomas, which are the most common tumour of infancy, and vascular malformations. These two categories, while related, require different treatment. Hemangiomas are benign and will regress but vascular malformations will continue to grow.
Hemangiomas are abnormally dense collections of dilated small blood vessels (capillaries) that may occur in the skin or internal organs. They may be present anywhere on the body. The classically recognized hemangioma is a visible red skin lesion that may be superficial in the skin (in the top layers, called a capillary hemangioma), deeper in the skin (cavernous hemangioma), or a mixture of both. Hemangiomas are usually present at birth although they may appear within a few months of birth often beginning at a site that has appeared slightly dusky or colored differently than the surrounding tissue. Hemangiomas, both deep and superficial, undergo a rapid growth phase in which their volume and size increase rapidly. This phase is followed by a rest phase, in which the hemangioma changes very little, and an involutional phase where the hemangioma undergoes spontaneous regression. During the involutional phase, hemangiomas may disappear completely. Large cavernous hemangiomas distort the skin around them and despite full involution, will ultimately leave visible changes in the skin. The more superficial capillary hemangioma may involute completely, leaving no evidence of its past presence.