Why is my nail black after I hit it?

The black is blood. The hit broke small vessels in the nail bed, and the blood had nowhere to go - the nail seals it in place like a bruise under glass. The NHS confirms what happens next: nails can change colour, become loose, and eventually fall off after an injury, and that is a normal sequence, not a disaster. The timeline is the long part: the discoloured section does not turn pink again - instead a fresh nail grows from the base and slowly pushes the damage out. The NHS puts regrowth at about 6 months for a fingernail and up to 18 months for a toenail. Right after the injury, ice the finger or toe and keep it raised to limit the bleed. The exception worth knowing: if the pressure builds enough, the throbbing can be fierce, and MedlinePlus describes the fix - a clinician can create a small hole in the nail to drain the blood and relieve the pressure, a quick job best done within the first day or two. Do not attempt that one at home. See a doctor too if the nail bed or surrounding skin is cut, if the finger looks bent or you cannot rule out a broken bone, or if the area later gets redder, more swollen, weeps pus, or you develop a fever - trapped blood plus a wound can infect. Otherwise the black nail is a waiting game: trim what loosens, protect the bed, and let the new nail arrive. Pymander is a free AI doctor, 24/7 by text, that can help you judge yours.