Even minor trauma to the finger may cause changes in the nail. The nail may develop a small spot of white discoloration that starts at the injury location and grows up with the nail.
Severe damage to the nail bed, particularly from a crush injury, often results in permanent nail deformity. To reduce the risk of a permanent nail deformity, the injury should be repaired immediately (which requires removal of the nail).
Blood often collects under the nail (subungual hematoma) immediately after an injury (usually a direct blow, such as with a hammer). The blood appears as a purple-black spot beneath part or all of the nail and causes a great deal of pain. The doctor can release the blood and relieve the pain by making a small hole in the nail plate. Usually the doctor uses a heated wire (electrocautery device) to burn the hole. This procedure is painless and takes only a few seconds.
Because the blood has separated the nail from its bed, the nail usually falls off after several weeks, unless the hematoma is small. A new nail grows below the existing nail and replaces it when fully grown in.
A tumor beneath the nail can cause a similar purple-black spot, although such a spot appears slowly and not within minutes of an injury. However, any small hematomas should be watched to make sure that they grow out with the nail. Growing out with the nail distinguishes hematomas from tumors because tumors remain in the same spot under the nail.
Last full review/revision August 2007 by Wingfield E. Rehmus, MD, MPH