My daughter has had a spot on her behind since birth. It is about the size of a half dollar and it looks just like a bruise but never goes away. She's two years old now. I always forget what it´s called. Will it ever go away?
The blue-black or slate-colored mark you describe is most likely a "Mongolian" spot. These are located on the lower back or buttocks and are badly named, since babies from the region of Mongolia are not the only ones born with them. In fact, up to 80 percent of Asian and African-American newborns have Mongolian spots, though only about 10 percent of Caucasian babies do.
They are harmless, cause no symptoms but take a long time to fade, usually diappearing by late childhood—or when girls begin to care how they appear in a bikini!