A black toenail occurs when blood collects under the nail after trauma, creating what’s known as a subungual hematoma. This condition often results from stubbing the toe, dropping something heavy on it, or repetitive pressure - common in runners or hikers.
The blood buildup is usually caused by injury to the small blood vessels beneath the nail. Tight-fitting shoes or activities that repeatedly jam the toes against the front of the shoe can also lead to this condition. In some cases, the nail may eventually loosen or fall off as new nail growth pushes it out.
Symptoms include dark discoloration (black, blue, or purple) under the nail, throbbing pain, and pressure. Your foot specialist can diagnose a subungual hematoma by examining the nail and may relieve pain by draining the blood if necessary. Imaging may be done if a fracture is suspected.
