Black Toenail: Causes, Treatment, and When to See a Podiatrist

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

What Causes a Black Toenail?

A black or dark toenail — medically called a subungual hematoma when caused by bleeding under the nail plate — is one of the most common foot complaints, particularly in runners and athletes. Understanding the different causes of nail discoloration is important, because while most black toenails are benign and self-resolving, a small number require urgent evaluation.

Subungual Hematoma: The Most Common Cause

A subungual hematoma is a collection of blood beneath the nail plate, caused by direct trauma to the toe. The blood appears dark purple, maroon, or black through the translucent nail. The most common mechanisms are: stubbing the toe against a hard surface, dropping a heavy object on the toe, repetitive microtrauma from a shoe that is too short (runner’s toe), and sudden deceleration in sports where the foot slides forward inside the shoe.

Immediately following the injury, the pooling blood under the nail creates significant pressure — this is the source of the throbbing pain that accompanies large hematomas. Small hematomas covering less than 25% of the nail area are typically managed with observation. Larger hematomas, or those causing severe pain, benefit from nail trephination — creating a small hole through the nail to release the blood and relieve pressure.

Nail Trephination: Draining the Hematoma

Nail trephination is a simple office procedure performed with a heated cautery device or a fine drill — typically using a heated needle — creating a small opening through the nail plate to drain the accumulated blood. The procedure itself is essentially painless because pressure makes the nail insensate. Within moments of drainage, pressure relief is dramatic and pain resolves significantly.

Trephination is most effective when performed within 24–48 hours of the injury, before the blood begins to coagulate and harden. After 48–72 hours, the hematoma may have solidified and trephination is less effective. At that point, nail avulsion (removal of the nail) may be needed if significant pain persists.

What Happens to the Toenail?

Following a large subungual hematoma, the nail typically separates from the nail bed over the following weeks as the nail bed heals and the nail plate detaches from below. The old nail loosens and eventually falls off, with a new nail growing in from the nail root. New nail growth occurs at approximately 1 mm per month — full nail regrowth of the great toenail takes 9–12 months.

During the transition period, the exposed nail bed requires protection with a bandage or tubular gauze to prevent discomfort and infection. Topical antibiotic ointment reduces infection risk during the vulnerable period between nail loss and new nail coverage.

Ruling Out Subungual Melanoma

The most serious differential diagnosis for nail discoloration is subungual melanoma — a rare but potentially deadly skin cancer occurring beneath the nail. Unlike a hematoma, melanoma grows from the nail matrix (root) and tends to produce a longitudinal brown-black streak (melanonychia striata) rather than a diffuse stain. Key warning signs: a pigmented streak that extends from the nail plate onto the skin around the nail (Hutchinson’s sign), a streak that is widening or darkening, nail discoloration without any history of trauma, and multiple colors within the lesion.

If you have nail discoloration without a clear traumatic history — or if discoloration persists for longer than a nail growth cycle without new nail growing in from the root — prompt evaluation is warranted. A nail biopsy may be recommended. Subungual melanoma has a worse prognosis than other melanoma types because it is frequently diagnosed late due to being mistakenly attributed to trauma.

Runner’s Toe: Chronic Nail Trauma

Runners who repeatedly sustain black toenails in the same toe should evaluate their shoe fit. The most common cause is a shoe that is too short — the great toe (or longest toe, which is sometimes the second) strikes the toebox repeatedly during downhill running or with prolonged forward foot slide. Shoes should be fitted with a thumbnail’s width of space in front of the longest toe. Running socks without seams reduce friction. Lacing techniques (toe-box lacing modifications) can reduce forward slide.

When to See Dr. Tom

Seek podiatric evaluation for: large hematomas causing severe pain (trephination needed), any nail trauma with suspected underlying fracture, nail discoloration without clear traumatic history, nail discoloration that doesn’t resolve as a new nail grows in, signs of infection under the nail (pus, increasing pain, foul odor), and any melanonychia striata (pigmented longitudinal band) that is new, widening, or concerning. Balance Foot & Ankle — Howell and Bloomfield Township — call (810) 206-1402.

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Black Toenail Treatment

A black or bruised toenail (subungual hematoma) can result from trauma, repetitive pressure from shoes, or underlying nail conditions. At Balance Foot & Ankle, we provide safe drainage and proper evaluation to ensure nothing more serious is occurring.

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Clinical References

1. Roukis TS. “Subungual Hematoma.” Clinics in Podiatric Medicine and Surgery. 2004;21(4):567-589.
2. Jellad A, et al. “Subungual Hematoma in Athletes.” Physician and Sportsmedicine. 2014;42(1):85-90.
3. Wollina U. “Acute Paronychia: Comparative Treatment with Topical Antibiotic Alone or in Combination with Corticosteroid.” Journal of the European Academy of Dermatology and Venereology. 2001;15(1):82-84.