Black, thick toenail: causes and next steps

Blood trapped beneath the nail can create a dark patch after an impact or ongoing shoe pressure. Thickening, crumbling, lifting or debris beneath the nail may also occur with a fungal nail infection. An examination helps distinguish these patterns, especially when there was no clear injury.

A bruise beneath the nail often stays in one area and gradually moves towards the tip as the nail grows. Repeated rubbing from tight footwear can cause similar damage without a memorable single accident. Fungal changes more often make the nail rough, brittle or distorted and may affect neighbouring nails.

A dark streak or patch that begins without trauma, widens near the cuticle, changes shape, or colours the surrounding skin needs prompt assessment. These features do not establish a diagnosis, but a clinician should examine them to exclude a pigment-producing growth, including melanoma beneath the nail.

Wear shoes with enough toe room, keep the foot clean and dry, and trim only the free edge without digging into the sides. Do not drill, puncture or pull at the nail yourself; opening it can introduce infection and may injure the nail bed. Photographing the nail in similar lighting can help show whether the dark area is growing outward.

Arrange a routine appointment if thickening persists, the cause is unclear, or several nails are changing. A clinician may inspect the nail, ask about footwear and injuries, and take a clipping or sample when infection is suspected. Treatment depends on the cause rather than colour alone.

Seek urgent care after a significant toe injury if pain is severe, the toe looks bent, bleeding will not stop, or you cannot bear weight. Rapidly increasing redness, warmth, swelling, pus, fever or red streaking can signal infection and also warrants prompt attention.

Book an early dermatology assessment for unexplained dark pigment that spreads, reaches the skin beside the nail, or does not travel towards the tip with nail growth. People with diabetes, reduced circulation, numb feet or weakened immunity should obtain professional advice before attempting nail care.

Ask whether the pattern fits bruising, infection or another nail disorder; whether a nail sample or closer examination is appropriate; and how to trim the thickened nail safely. You can also ask what visible change should trigger a faster follow-up and whether your footwear is adding pressure.