Guide · Feet
Black toenails from running
Quick answer
A black toenail from running is usually bleeding under the nail (a subungual hematoma) caused by the toe repeatedly hitting the front of the shoe, especially on downhills or in shoes that are too short. Prevent it with enough toe room, short nails and good lacing. Don't pull off a loose nail. See a doctor for throbbing pain or a dark streak that you can't link to an injury, which can rarely be melanoma.
- Runner's toe comes from repeated toe strikes against the shoe, a small toe box and downhill running.
- Keep nails short, get shoes with toe room and lace to stop the foot sliding forward.
- Never drain it at home; a clinician can relieve painful pressure.
- A dark streak with no clear injury, or one that doesn't grow out, should be checked for melanoma.
What causes it
Cleveland Clinic explains runner's toe as repeated trauma: the toe strikes the front or top of the shoe over thousands of steps, made worse by a toe box that's too small and by downhill running.[1] The trauma causes bleeding under the nail, called a subungual hematoma.[2]
How to prevent it
- Shoes with enough length and toe-box height; feet swell late in long runs.
- Trim toenails short and straight across a few days before a race.
- Lace to hold the heel in place so the foot doesn't slide forward on descents.
- Moisture-wicking socks; some runners use silicone toe pads.[1]
What to do if you have one
Leave it alone if it isn't painful. Don't pull off a loose nail.[1] A throbbing, pressured nail can be drained by a clinician; Cleveland Clinic advises never draining it at home. A lost nail takes about 6 to 9 months to grow back.[2]
When a dark nail needs a doctor
The American Academy of Dermatology lists warning signs of nail melanoma: a brown or black streak, often on the big toe, darkening of the skin next to the nail, or a nail that lifts or splits. A past injury doesn't rule it out.[3] If a dark area doesn't grow out with the nail or you can't remember an injury, get it checked.
FAQ
Will a black toenail from running fall off?
Sometimes. If it loosens, let it come off on its own and keep the area clean and covered. A new nail takes about 6 to 9 months to grow.
Are black toenails a sign of bad shoes?
Often. Shoes that are too short or shallow in the toe box are a common cause, along with long nails and downhill running.
Sources
- How to prevent and treat runner's toe. Cleveland Clinic.
- Subungual hematoma. Cleveland Clinic.
- Nail melanoma. American Academy of Dermatology.
