Birthmarks are not caused by stress or aging; they are caused by extra pigment in the skin or blood vessels that bunches together under the skin, according to WebMD. It is unknown why some people have birthmarks, and others do not.
There are a variety of birthmarks a person may develop, including salmon patches, congenital moles, cafe-au-lait spots and Mongolian spots, explains WebMD. Hemangiomas and port wine stains are also common birthmarks.
Salmon patches are light, thin, and red or pink, often appearing on the back of the neck or around the forehead, states WebMD. Congenital moles are brown, and they can appear on any area of the body. Cafe-au-lait spots appear on the torso, legs or buttocks and are smooth. These spots range from light brown to chocolate brown in color.
Mongolian spots are typically uneven and blue or blue-gray in color. They often appear on the buttocks or lower back, asserts WebMD. Hemangiomas are raised off of the skin, and they are red, blue or purple in color. They can appear anywhere on the skin and may even grow deep into the body. Port wine stains appear as pink or red at birth, and they usually darken over time.