Black Toenail: Causes, Treatment & When to Worry | DPM

Quick answer:A subungual hematoma is blood trapped under the toenail after an injury, leaving it dark and often throbbing. Our Michigan podiatrists can relieve the pressure to ease the pain, check for an underlying fracture, and monitor the nail as it grows out over several months. Call (810) 206-1402.

Medically reviewed by Dr. Tom Biernacki, DPM — Board-Certified Podiatric Surgeon — Balance Foot & Ankle, Howell & Bloomfield Township, MI. Last updated April 2026.

A black toenail from a subungual hematoma — blood trapped under the nail after trauma — is common and usually resolves on its own as the nail grows out. However, a persistent dark streak under the nail without a clear trauma history requires immediate evaluation to rule out subungual melanoma, which can be fatal if diagnosed late. Dr. Tom Biernacki, DPM at Balance Foot & Ankle in Howell and Bloomfield Township, Michigan evaluates and treats black toenail conditions with particular attention to the important diagnostic distinction between hematoma and melanoma.

What Causes a Black Toenail?

The most common cause is direct trauma — dropping something on the toe, stubbing the toe, or repetitive microtrauma in runners where the longest toe repeatedly impacts the front of the shoe. The trauma causes bleeding between the nail plate and the nail bed. As blood pools and oxidizes, it turns black or dark red-brown. The pressure from the hematoma can be painful, particularly in the first 24–48 hours. In runners, black great toenail or second toenail is extremely common after long training runs or races — the second toe is often the longest and contacts the shoe with every stride.

Treatment: When to Drain vs. Wait

Subungual hematomas involving more than 25–50% of the nail surface area with significant pain may benefit from trephination — creating a small hole through the nail to drain the accumulated blood and relieve pressure. This is performed in-office with a heated wire (electrocautery) or a fine drill bit, is essentially painless, and provides immediate pressure relief. Hematomas involving less than 25% of the nail surface area, or those presenting after 24–48 hours when clot has organized, do not typically benefit from drainage and are managed with observation. The nail will eventually fall off and regrow over 6–12 months as the hematoma grows out.

The Critical Warning Sign: Melanoma vs. Hematoma

Subungual melanoma is a rare but serious skin cancer that presents as a dark streak under the nail — visually identical to a subungual hematoma. Missing this diagnosis is a potentially fatal error. The key differentiating features: a hematoma has a clear trauma history and moves distally as the nail grows over weeks to months (photograph the nail at presentation and compare at 3–4 weeks); a melanoma is a fixed pigmented streak that does NOT move with nail growth, often features irregular borders at the nail fold (Hutchinson’s sign — pigment extending to the skin adjacent to the nail), and has no trauma history. Any dark nail discolouration without a clear trauma history requires biopsy or dermatology/podiatry evaluation — not watchful waiting.

Hutchinson’s Sign: A Dermatologic Emergency

Hutchinson’s sign is the extension of dark pigmentation from under the nail onto the surrounding nail fold (the skin next to the nail). It is a specific finding for subungual melanoma and constitutes a dermatologic emergency requiring immediate biopsy. In a subungual hematoma, discolouration does not extend beyond the nail plate. Any patient with dark nail pigmentation and Hutchinson’s sign should be seen urgently by a podiatrist or dermatologist for nail biopsy regardless of trauma history — subungual melanoma can occur on a traumatized nail.

Runner’s Black Toenail Prevention

Runners can significantly reduce black toenail incidence with proper shoe fitting: ensure a full thumb’s width between the longest toe and the end of the shoe (foot measurements at the end of a run when feet are most swollen), use thin moisture-wicking socks that reduce friction-related microtrauma, keep toenails trimmed straight across at or slightly below the longest toe tip, and consider silicone toe caps for the most commonly affected toes during ultra-distance events. In patients with recurrent runner’s black toenail, custom orthotics with metatarsal accommodation can reduce the toe-strike pattern that causes nail trauma.

Most Common Mistake With Black Toenail

The most common mistake is assuming all dark toenail discolouration is from trauma and never having it evaluated. Subungual melanoma of the foot accounts for a disproportionate share of all-cause melanoma mortality because it is diagnosed late — patients (and sometimes clinicians) assume it is a persistent bruise. The rule: any dark toenail without a confirmed trauma history, or any dark streak that does not move distally over 3–4 weeks, requires biopsy evaluation.

When to See a Podiatrist

See a podiatrist same-day for significant pain from a subungual hematoma (trephination provides immediate relief), within 1–2 weeks for a dark toenail without clear trauma history, and urgently for any dark pigmentation extending to the nail fold (Hutchinson’s sign). Dr. Biernacki evaluates subungual hematoma and nail pathology with dermoscopy when appropriate, performs in-office trephination for painful hematomas, and coordinates biopsy for nail lesions requiring histopathological evaluation. Call (810) 206-1402 or book online — Howell and Bloomfield Township, Michigan.

Visit Balance Foot & Ankle — Same-Day Appointments Available

Our podiatry team serves patients throughout Michigan including Howell, Brighton, and Bloomfield Township. If you’re dealing with heel pain, ingrown toenails, or a foot injury, we have same-day appointment availability.

Frequently Asked Questions

How long does it take a toenail to grow back?

6-12 months for a full big toenail. Smaller toenails 4-6 months. Speed varies with age, circulation, and nutrition.

Will this affect other nails?

Trauma affects only the injured nail. Fungal infection can spread without treatment. Systemic causes affect multiple nails simultaneously.

Should I cover the nail or leave it open?

Cover with a breathable bandage during work or activity. Leave open at night for healing. Keep dry and clean.