Black Skin Under a Toenail: Causes and Next Steps

Blood can collect beneath the nail after stubbing the toe, dropping something on it, running, or wearing shoes that repeatedly press the nail. This is called a subungual haematoma. It may look red-purple at first and later turn brown or black. The mark should gradually move towards the nail tip as the nail grows.

Other explanations include fungal nail disease, staining, or pigment made within the nail unit. Subungual melanoma can present as a new or changing dark band, especially when pigment spreads onto the nearby skin. Appearance alone cannot reliably separate these causes.

If there was a minor injury, protect the toe, use roomy footwear, and keep the nail clean and dry. A wrapped cold pack can ease early swelling; avoid placing ice directly on skin. Do not pierce, cut, or burn through the nail at home, because this can injure the nail bed and introduce infection.

Take a clear photograph and note whether the dark area travels outward with nail growth. Arrange an assessment if there was no injury, the colour remains fixed near the nail base, or the nail becomes thick, crumbly, distorted, or detached.

Seek prompt care after a crushing injury, for severe throbbing pain, or if the toe looks bent or is difficult to bear weight on. A clinician can check for a fracture or nail-bed injury and decide whether trapped blood should be drained safely.

Get urgent advice if redness is spreading, warmth or swelling is increasing, pus appears, or you feel feverish. Book a dermatology assessment for a new dark streak without clear trauma, widening or irregular pigment, colour extending onto the cuticle or surrounding skin, bleeding, or a change affecting only one nail. People with diabetes, reduced circulation, numb feet, or a weakened immune system should seek advice early rather than treating the toe themselves.

Ask whether the pattern fits trapped blood, infection, or pigment arising in the nail unit; whether the nail bed or bone may be injured; and what changes should trigger reassessment. If a procedure is proposed, ask what it involves, how to protect the toe afterwards, and when normal footwear and activity can resume.