You finished a 10 km proud of your time, then when you took off your sneakers, shock: a toenail had turned black. For many runners, that first black nail comes with the increase in kilometers. Some see it almost as a necessary step. Others are mainly concerned about the pain and appearance.
What we call black running toenail, or subungual hematoma, corresponds to blood stuck between the nail and the nail bed after repeated micro-trauma. The phenomenon is common among joggers and marathon runners, but it most often remains benign when it follows an identifiable effort.
Runner’s black nail: what happens under the nail
With each stride, especially when going downhill, the toes come up against the front of the running shoes. The small vessels under the nail rupture, an effusion forms, first red or purplish, then dark brown. The big toe and the second toe are the most exposed among trail runners and long outing enthusiasts.
When the affected surface is limited and not very painful, the nail plays the role of a natural dressing. A toenail generally takes between six and twelve months to completely grow back, with the new healthy nail eventually growing back and gradually removing the damaged plate.
Black nail when running: causes to watch out for
In most cases, the main cause remains the shoe. Too tight, it compresses a foot which swells during exercise; too big, it lets the foot slide forward. Prolonged descents accentuate this phenomenon, especially if the lacing is loose and if the nails are too long. Thick cotton socks that retain moisture also increase friction, hence the importance of breathable technical socks.
Socks and skin condition also play a role. The running coach sums up the situation well: explains Martin Yelling to Red Bull.
Preventing and managing a black nail after running
To avoid black nails, it all starts with the equipment and a few simple steps. The idea is to reduce repeated impact on the toes and continued pressure in the shoe over long distances, such as preventing runner injuries.
If, despite everything, a nail turns black but remains minimally painful, clean the foot, protect the area and let it grow back; you can continue running if the shoe doesn’t hurt. Severe throbbing pain, significant swelling, fever or black nail without trauma should lead to consulting a sports podiatrist or a doctor to rule out fracture, infection, nail fungus or more rarely subungual melanoma.
Can I continue running with a black toenail?
Yes if the pain is mild and the shoe does not compress the affected toe. Stop as soon as it pulses.
How long does it take for the nail to grow back?
It often takes between six and twelve months to regain a completely healthy toenail.
When should I consult for a black nail?
If the pain is severe, the nail becomes widely detached or the color changes without a clear sporting reason.
