There are two broad categories of birthmarks: vascular and pigmented. Vascular birthmarks are often reddish because, as the name indicates, they're caused by enlarged blood vessel formations. The most common vascular marks are macular stains, hemangiomas and port-wine stains.
Macular (or flat) stains are often called salmon patches, angel kisses or stork bites. These marks almost always appear in areas above the neck, and although some last for many years, most disappear by the age of two.
Port-wine stains are another type of vascular birthmark. Their blotchy appearance looks a little bit like spilled wine. These marks are caused by abnormally developed blood vessels and they may become larger as a child ages. Unlike some other vascular birthmarks, port-wine stains never go away and often darken and may become more obvious with age. Although they generally can't cause health issues, if these appear near the eyes they can cause complications with vision, so a doctor may need to take action.
Hemangiomas, also called strawberry marks, are often raised and easy to differentiate from surrounding skin. About 30 percent of affected babies are born with these marks, while the other 70 percent of affected babies manifest their marks within four weeks of birth [source: Vascular Birthmarks Foundation]. Most of these marks have a reddish color due to the clusters of blood vessels that form them, however, hemangiomas extending deeper into the skin have a bluish cast.
Most hemangiomas disappear by the time a child reaches the age of 10, and as larger formations fade they may leave a scar. These kinds of marks can appear anywhere on the body, but most frequently affect the head and neck. They are most common in Caucasian girls.
Unlike most birthmarks, hemangiomas may have serious impact on a child's development. Their sometimes significant size and puffy structure can interfere with hearing, vision, breathing, eating and other critical bodily functions. Internal hemangiomas can grow on organs such as the liver, brain and intestines, and in some circumstances, they can be deadly. These growths are very difficult to detect, although some doctors have found success locating them with ultrasound.