Medically reviewed by Dr. Tom Biernacki, DPM — Board-Certified Podiatric Surgeon — Balance Foot & Ankle, Howell & Bloomfield Hills, MI. Last updated April 2026.
What Causes Black Toenail in Runners?
Black toenail in runners—medically called subungual hematoma—is one of the most common running-related foot problems. It occurs when repetitive microtrauma causes bleeding beneath the toenail plate, creating a hematoma (collection of blood) in the space between the nail and the nail bed. In runners, the mechanism is repetitive impaction of the toe against the front or top of the shoe with each running stride—most commonly affecting the longest toe (the second toe in runners with Morton’s toe, or the first toe in others). The trapped blood darkens from red to purple to black-brown over days as it desiccates.
Acute onset black toenail can also result from a single significant trauma—stubbing the toe, dropping a heavy object on it, or a single-session run in particularly ill-fitting shoes. The clinical presentation is the same, but the history distinguishes them. Runners are also susceptible to nail changes from fungal infection (onychomycosis), which can cause discoloration ranging from yellow to black, though fungal nail changes are typically thicker, more brittle, and associated with debris under the nail.
Symptoms and What to Expect
A subungual hematoma may or may not be painful depending on the pressure it creates. Small hematomas are often painless and discovered incidentally when removing socks after a long run. Larger hematomas create significant pressure under the nail that causes throbbing pain—if pain is severe and pressure is significant, the nail may need to be trephined (a small hole made through the nail to release the pressure). After the initial period, the pain typically resolves as the pressure equilibrates or the blood reabsorbs. The nail will eventually fall off as the new nail grows in beneath—a process that takes 6–9 months for a toenail to fully grow out. The new nail may have some ridging or irregularity but usually grows in normally.
Prevention
The most effective prevention is proper shoe fit. Running shoes should be half a size to a full size larger than street shoes to accommodate foot swelling and forward movement during running. There should be approximately a thumb-width (10–15mm) of space between the end of the longest toe and the front of the shoe when standing. Lacing technique matters—keeping the shoe snug over the midfoot with the Heel-Lock lacing method prevents the foot sliding forward with each stride. Keep toenails trimmed short (straight across, not too short)—long nails catch on the shoe more readily. Moisture-wicking socks that fit without bunching reduce friction.
When to See a Doctor
Most runner’s black toenails require no medical treatment—watchful waiting and proper shoe fit correction are sufficient. See a podiatrist if: the hematoma is very painful and the nail needs to be trephined for pressure relief (an in-office procedure), you are uncertain whether the discoloration is a hematoma vs. fungal nail vs. more serious pathology, the dark discoloration does not grow out with the nail over several months, the discoloration extends beyond the nail onto the surrounding skin (Hutchinson’s sign—a warning sign for subungual melanoma), or the nail appears infected (increasing redness, swelling, pus). Any black or dark streak under the nail that did not result from clear trauma, that does not move distally as the nail grows, or that has irregular borders should be evaluated promptly to rule out subungual melanoma.
Frequently Asked Questions
Should I drain a black toenail?
Draining (trephining) a subungual hematoma is appropriate only if it is significantly painful—if pressure under the nail is causing throbbing discomfort that limits normal activity or prevents sleep. Small, painless hematomas do not need draining and should be left alone. Trephination is an in-office procedure where a small hole is made through the nail (using a heated wire or needle) to release the trapped blood and relieve pressure. It should be done within the first 24–48 hours when the blood is still liquid; older, clotted hematomas cannot be drained effectively. Do not attempt to drain your own toenail at home with a sharp object—this risks infection and additional nail damage. If you have significant pain from a black toenail, a podiatrist can assess whether trephination is appropriate and perform it safely.
How long does a black toenail take to heal?
The timeline depends on whether the nail falls off and how much of the nail is affected. If the nail remains attached (small hematoma), it will grow out over 6–9 months as the new nail pushes the old nail forward. If the nail separates and falls off (more extensive hematomas), the new nail begins growing immediately but takes 6–9 months to fully replace the lost nail. During this period, runners can continue training—the underlying nail bed is not usually significantly painful once the initial pressure resolves—with a bandage covering the exposed nail bed if the nail has separated. Some runners use a gel toe protector for comfort. The new nail may grow in with some initial ridging or abnormality but usually normalizes by the time it is fully grown.
Can I keep running with a black toenail?
Yes—most runners can continue training with a black toenail once the initial pain settles (typically within a few days). If the nail is not loose and is not significantly painful with running, continuing at normal training is generally safe. If the nail is loose (attached only partially), apply a small piece of athletic tape over it to protect the nail bed during runs—do not forcibly remove a partially attached nail. Address the shoe fit issue before returning to training to prevent recurrence: ensure adequate toe box length (half to full size up) and use a heel-lock lacing technique. If running continues to cause significant toe pain, a brief reduction in mileage and a shoe fit evaluation are warranted before resuming full training.
Medical References & Sources
- PubMed Research — Subungual Hematoma in Runners
- PubMed Research — Running Shoe Fit and Foot Injuries
- American Podiatric Medical Association — Nail Conditions
Dr. Tom Biernacki, DPM is a board-certified podiatric surgeon at Balance Foot & Ankle in Howell and Bloomfield Hills, Michigan. He evaluates nail conditions in runners including subungual hematomas, nail fungus, and pigmented nail lesions, providing accurate diagnosis and appropriate treatment.
Dr. Tom’s Recommended Products for Toenail Problems
📍 Located in Michigan?
Our board-certified podiatrists treat this condition at two convenient locations. Same-day appointments often available.
These are products I personally use and recommend to my patients at Balance Foot & Ankle.
- Nail Tek Intensive Therapy II — Restores brittle, discolored, and damaged nails — base coat that strengthens nail plate after trauma or fungal damage
- Kerasal Fungal Nail Renewal — Visibly improves nail appearance for both fungal and non-fungal discoloration within 8 weeks
- Professional Toenail Clipper — Harperton Nail Nipper — Stainless steel curved jaw cuts thick or ingrown toenails cleanly — prevents nail trauma and subungual hematoma
📧 Get Dr. Tom’s Free Lab Test Guide
Discover the 5 lab tests every person over 35 should ask their doctor about — explained in plain English by a board-certified physician.
Affiliate disclosure: As an Amazon Associate, Balance Foot & Ankle earns from qualifying purchases. We only recommend products we trust for our own patients.
Join 950,000+ Learning About Foot Health
Dr. Tom shares honest medical advice, supplement reviews, and treatment guides you won’t find anywhere else.
Subscribe on YouTube →Medically Reviewed by: Dr. Jeffery Agnoli, DPM — Board-Certified Podiatrist, Balance Foot & Ankle Specialists
Black Toenail From Running?
A black toenail may be a simple bruise — or it could signal a subungual hematoma that needs drainage. Our podiatrists can evaluate it quickly and get you back to training.
Sources
- Mailler EA, Adams BB. “The wear and tear of 26.2: dermatological injuries reported on marathon day.” Br J Sports Med. 2004;38(4):498-501.
- Vlahovic TC. “Black toenails: what to do about them.” Podiatry Today. 2015;28(2):34-38.
- Richert B, André J. “Nail disorders in runners and athletes.” Clin Dermatol. 2013;31(5):576-588.
Dr. Tom Biernacki, DPM is a double board-certified podiatrist and foot & ankle surgeon at Balance Foot & Ankle Specialists in Southeast Michigan. With over a decade of clinical experience, he specializes in heel pain, bunions, diabetic foot care, sports injuries, and minimally invasive surgery. Dr. Biernacki is a member of the APMA and ACFAS, and his patient education content on MichiganFootDoctors.com and YouTube has reached over one million views.
Related Treatments at Balance Foot & Ankle
Our board-certified podiatrists offer advanced treatments at our Bloomfield Hills and Howell locations.
Recommended Products from Dr. Tom