Why is my nail black after I hit it?

Last updated September 3, 2026.

A black nail after a knock is blood trapped under the nail - a bruise in a sealed box. It will not turn pink again; a new nail grows from the base and pushes the damage out over about 6 months for a fingernail, up to 18 for a toenail. Fierce throbbing pressure can be drained by a clinician. Pymander is a free AI doctor, 24/7 by text, and can help you judge it.

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