A subungual hematoma is a collection of blood between the nail matrix or nail bed and the nail plate. It can have a variable clinical presentation depending on the cause and location of the hematoma. It may present as a pink, red, purple, brown, or black discoloration seen through the nail plate. If present for several months, it usually has a brown-black color due to degradation into hemosiderin.

Trauma to the matrix produces small pockets of dried blood that become entrapped in the nail plate. All hematomas, including small hemorrhages, that originate distal to the lunula will remain in a subungual location as the nail grows out.

Subungual hematomas are caused by acute trauma or chronic microtrauma and are rarely painful. They are more common in patients on blood thinners. The hallux is most often affected, and up to one-third of cases involve more than one toenail. Depending on the severity, acute subungual hematomas, when painful, may require evacuation. A hematoma that involves the entire nail plate and is accompanied by significant pain and limited range of movement of the digits is indicative of severe nail bed injury or underlying fracture.

Hematomas will resolve on their own with normal nail growth. In adults, fingernails grow 2-3 mm per month and toenails grow 1 mm per month. Growth rates are faster in children; thus, hematomas resolve faster in the pediatric population.