Black Toenail: Causes, When to Worry, and Treatment Options

Table of Contents

1. Causes of Black Toenail
2. Subungual Hematoma: The Most Common Cause
3. Black Toenail and Melanoma: When to Worry
4. Runner’s Black Toenail: Prevention and Treatment
5. Treatment Options
6. Best Products for Black Toenail Care
7. Warning Signs Requiring Immediate Evaluation
8. Frequently Asked Questions
9. The Bottom Line

A black toenail stops most people in their tracks — it looks alarming, and rightfully so. The good news is that the vast majority of black toenails are the result of blood pooling under the nail from minor trauma, and they resolve completely as the nail grows out. The important news is that not every dark toenail is a hematoma — and the rare cases that aren’t deserve urgent attention. In our clinic, we see black toenails weekly; after reading this guide, you’ll know exactly what you’re looking at and what to do about it.

Causes of Black Toenail

Black discoloration under or around a toenail has several distinct causes, each with different clinical implications:

• Subungual hematoma — Blood pooled between the nail plate and nail bed from trauma or repetitive pressure. The most common cause. Appears dark red, maroon, brown, or black. Usually painful initially, then less so as pressure equalizes.
• Toenail fungus (onychomycosis) — Advanced fungal infection can produce yellow-brown discoloration that appears dark, and debris accumulation under the nail can look black. Distinguished from hematoma by the presence of nail thickening, brittleness, and debris rather than fluid.
• Subungual melanoma — A melanocytic lesion (melanoma) developing in the nail matrix produces a dark streak or spot under or within the nail plate. Rare but serious. Not associated with trauma. Requires urgent biopsy.
• Subungual exostosis — A bony growth beneath the nail plate that exerts upward pressure can cause nail discoloration and lifting without trauma.
• Medication side effects — Certain medications (hydroxyurea, antimalarials, some chemotherapy agents) can cause diffuse nail pigmentation changes.
• Ethnic nail pigmentation (melanonychia striata) — Linear brown or black bands in the nail are normal in people with darker skin tones and should not be confused with melanoma — but evaluation by a dermatologist or podiatrist is warranted if new or changing.

Subungual Hematoma: The Most Common Cause

A subungual hematoma forms when blood vessels in the nail bed rupture from acute trauma (stubbing the toe, dropping something on it) or repetitive microtrauma (the toe striking the end of a shoe during running or hiking). Blood accumulates in the closed space between the nail plate and nail bed, creating pressure that produces the characteristic throbbing pain of a fresh hematoma and the dark red-to-black discoloration.

The appearance progresses predictably: fresh hematomas are bright red within the first hours; by 24–48 hours they darken to maroon, then brown-black as the blood desiccates. As the nail grows out over weeks and months, the dark area moves distally (toward the tip of the toe) at the nail growth rate of approximately 1–1.5mm per month. A big toenail takes 12–18 months to fully replace; a small toenail takes 6–9 months.

Key diagnostic feature: if you can clearly recall the trauma event that preceded the black nail by hours to days, and the black area is uniformly dark and corresponds to the nail bed, it is almost certainly a hematoma. If there’s no clear trauma history, the discoloration is a streak or spot rather than a uniform blush, or if the discoloration extends to the skin around the nail (Hutchinson’s sign), melanoma evaluation is urgent.

Black Toenail and Melanoma: When to Worry

Subungual melanoma represents approximately 2% of all melanomas in white-skinned populations and a higher proportion in darker-skinned populations, where hematoma is less likely to be mistaken for it. It is most commonly found on the great toenail or thumbnail. The features that distinguish melanoma from hematoma:

• No trauma history — Melanoma appears spontaneously. If you cannot identify a specific traumatic event that preceded the discoloration, evaluation is urgent.
• Longitudinal melanonychia — A dark streak running from the base of the nail to the tip (longitudinal banding), rather than a uniform dark blush in the middle of the nail.
• Hutchinson’s sign — Pigmentation extending from the nail onto the surrounding nail folds (the proximal or lateral nail fold skin). This is a major warning sign of subungual melanoma and requires immediate dermatologic or podiatric evaluation.
• Variegated color — Melanoma streaks often have multiple shades (dark brown, black, gray, tan) rather than the uniform dark red-black of a hematoma.
• The black area doesn’t move distally — A hematoma moves toward the nail tip as the nail grows. A melanoma remains in a fixed position relative to the nail matrix. If the dark area stays in the same location over 4–6 weeks without proximal movement, melanoma evaluation is warranted.

Subungual melanoma is highly treatable when caught early. The standard treatment for in-situ subungual melanoma is complete excision — often with nail removal and wide local excision of the nail matrix. Advanced subungual melanoma has the same prognosis as other Stage III-IV melanomas. Early diagnosis is life-saving.

Runner’s Black Toenail: Prevention and Treatment

Runner’s black toenail (also called “jogger’s toe”) is subungual hematoma caused by the repetitive impact of the toenail against the shoe during running — typically during downhill running, long-distance events, or running in shoes that are too short. The great toe and second toe (especially in Morton’s foot where the second toe is the longest) are the most commonly affected.

Prevention centers on proper shoe fit: the longest toe should have half an inch of space from the end of the shoe when standing. Many runners wear their running shoes too short to avoid the feeling of excess space, which backfires on long runs when the foot swells. Lacing techniques that create a “runner’s loop” or “heel lock” at the top eyelet can also reduce forward foot slide during downhill running — keeping the toes from repeatedly striking the shoe’s end.

For prevention, moisture-wicking socks that fit without bunching (Darn Tough, Balega) reduce friction. Keeping toenails trimmed straight across at or just below the top of the toe eliminates the leading edge that strikes the shoe first during downhill running.

Treatment Options

For Small, Painless Hematomas

The majority of small subungual hematomas (covering less than 25% of the nail area) in patients with intact nails and no trauma to the nail plate require no treatment. Clean the surrounding skin, trim any damaged nail edge with clean nail scissors, and protect the toe with a cushioned bandage. The nail will grow out over the coming months, and the dark area will migrate toward the tip until the nail is fully replaced.

For Large, Painful Hematomas

A hematoma covering more than 50% of the nail area, or any hematoma with severe throbbing pain, benefits from trephination — the creation of one or two small holes through the nail plate to release the blood and decompress the nail bed. This is performed in our clinic using a heated needle or a small drill bit under sterile conditions. The procedure is nearly painless (the blood under pressure is the source of pain, not the nail itself) and the pain relief is immediate upon drainage. Do not attempt home trephination with sharp objects — infection risk is significant.

Nail Loss

Large hematomas often result in complete nail loss — the nail plate separates from the nail bed and eventually falls off or is removed. This is not an emergency. A new nail will grow from the nail matrix in 6–12 months. Keep the exposed nail bed covered with a non-stick dressing (Telfa) and antibiotic ointment until the new nail provides coverage. If the nail hasn’t grown back within 12 months, evaluation for nail matrix damage is appropriate.

Best Products for Black Toenail Care

Nexcare No-Sting Liquid Bandage — Applied around the nail edge to protect the skin border from infection and friction while the hematoma resolves. Particularly useful for athletes who cannot take time off from training.

→ Find Nexcare No-Sting Liquid Bandage on Amazon

Compeed Blister Plasters — Hydrocolloid dressings that protect the nail and surrounding tissue when the nail plate has been lifted or partially detached. Stay adhered through activity and prevent secondary friction injury.

→ Find Compeed Blister Plasters on Amazon

Dr. Scholl’s Cushioning Bandage — Thick protective padding around the toe when the toenail is sensitive or partially separated, allowing continued walking and activity with reduced discomfort.

→ Find Dr. Scholl’s Cushioning Bandage on Amazon

Darn Tough Running Socks — For runners: moisture-wicking Merino wool socks that eliminate the friction and moisture that worsen toenail trauma during long runs.

→ Find Darn Tough Running Socks on Amazon

Frequently Asked Questions

Should I drain a black toenail at home?

No. Home drainage of subungual hematomas with needles, pins, or other unsterilized instruments carries significant infection risk and should never be attempted. Podiatric trephination in a clinical setting takes 5 minutes, is nearly painless, and is performed under sterile conditions with instruments sized appropriately for the nail plate. If your hematoma is causing significant throbbing pain, call our office — same-day appointments for acute nail pain are available.

How long does a black toenail take to heal?

The dark discoloration of a subungual hematoma takes as long as the toenail takes to grow out — approximately 6–9 months for lesser toes and 12–18 months for the great toenail. The dark area moves progressively toward the tip of the toe at the nail’s growth rate (about 1–1.5mm per month). The nail may or may not fall off completely; if it does, the new nail will take the same time to grow back from the matrix. Pain typically resolves within 2–4 weeks of the initial injury regardless of nail appearance.

Can you run with a black toenail?

In most cases, yes — after the acute pain has subsided (typically 2–5 days after the injury). Protect the nail with a hydrocolloid bandage and cushioned sock, and address the shoe-fit issue that caused the hematoma (add half a size to running shoe length). If the nail plate is partially detached, tape it down with a skin-safe tape (Hypafix or Nexcare) before running to prevent it from catching and being forcibly avulsed — painful and a meaningful infection risk.

The Bottom Line

Most black toenails are subungual hematomas — blood pooled under the nail from trauma — that resolve completely as the nail grows out. Small painless hematomas need only protection; large painful ones benefit from professional drainage. The non-negotiable caveat: any dark nail discoloration without a clear trauma history, any dark streak running longitudinally through the nail, or any pigmentation extending onto the skin around the nail fold requires urgent podiatric or dermatologic evaluation to rule out subungual melanoma. In this small but serious category, early diagnosis is genuinely life-saving.

Sources

1. Tan KB, et al. “Subungual melanoma: a study of 124 cases.” J Am Acad Dermatol. 2007;57(3):441–443. PubMed
2. Tully AS, et al. “Longitudinal melanonychia: evaluation and management.” J Am Acad Dermatol. 2011;65(4):812–819.
3. Cohen PR. “Longitudinal erythronychia: individual or multiple linear red bands of the nail plate: a review of clinical features and associated conditions.” Am J Clin Dermatol. 2011;12(4):217–231.
4. Tosti A, Piraccini BM. “Biology of nails and nail disorders.” Fitzpatrick’s Dermatology. 9th ed. McGraw-Hill; 2019.
5. Jellinek N. “Nail matrix biopsy of longitudinal melanonychia: diagnostic algorithm including the matrix shave biopsy.” J Am Acad Dermatol. 2007;56(5):803–810.