Birthmarks are areas of raised or flat discolored skin that are usually visible on a baby's skin at birth. They tend to be the result of an abnormal development of blood or lymph vessels, but no one knows the exact cause of all birthmarks. Certain types of birthmarks may not show up for several days or weeks after a baby's birth.
Some marks endure for life, while others fade away over time.
Birthmarks come in a wide range of shapes, sizes, and colors and can show up anywhere on a child's body. Moles, which vary in size and may be raised or flat, smooth or hairy, black or brown. Large ones are known as nevi . Bluish or greenish Mongolian spots on the back or buttocks, which usually fade by school age, although they may never disappear altogether. They are most common in babies with dark skin.