Why does my nail biter client have blood pooling under her nails?

This sounds like it may be a subungual hemorrhage, which is when blood gets trapped under the nail secondary to trauma, in this case from nail biting. However, there are many things, some serious, that can cause discoloration of the nail. If the problem persists I would recommend that she see a dermatologist.

— Dana Stern, M.D. is a board-certified dermatologist specializing in nails. She works in private practice in New York City.