A toenail that turns red, purple, brown, or black after a long run, hike, or day of walking can look alarming. In many cases, the discoloration is caused by repeated pressure inside the shoe rather than a single obvious injury.
The most common explanation is a subungual hematoma, which means that a small amount of blood has collected beneath the nail. Runners sometimes call this runner’s toe. It can develop when the toe repeatedly strikes the front or top of the shoe, especially during downhill movement or longer-than-usual activity.
However, not every dark toenail is a bruise. Fungal nail changes, infection, irritation around an ingrown nail, and certain pigment changes can sometimes look similar.
Usually caused by repeated impact, shoe pressure, or direct trauma.
A bruise commonly appears after a run, hike, impact, or day in tight shoes.
New, widening, irregular, or changing pigment should be professionally evaluated.
A black toenail that appears shortly after running, hiking, toe impact, or prolonged shoe pressure is often caused by bleeding beneath the nail. Arrange an examination if the pain is severe, the cause is unclear, the surrounding skin becomes inflamed, or the discoloration does not gradually move forward as the nail grows.
During running or hiking, the foot moves inside the shoe with every step. If a toe repeatedly touches the front, top, or side of the toe box, the pressure can damage small blood vessels beneath the nail. The resulting blood becomes trapped between the nail plate and the sensitive nail bed.
The discoloration may begin as red or purple and later become dark brown or nearly black. The nail may remain firmly attached, or it may gradually loosen if the underlying injury is more significant.
A shoe does not have to feel extremely tight to damage a toenail. A small amount of contact repeated thousands of times can be enough. At the same time, choosing an oversized shoe is not always the solution because excessive movement may allow the foot to slide forward.
Recurring problem? People who repeatedly develop nail trauma, blisters, forefoot pain, or other activity-related symptoms may benefit from a broader sports foot and ankle evaluation. The examination can consider footwear, nail health, pressure points, foot structure, and movement patterns rather than looking at the nail in isolation.
Runner’s toe does not look exactly the same in every person. Its appearance depends on how much blood has collected, where the trauma occurred, and whether the nail plate or nail bed was also injured.
A small hematoma may produce little or no pain. A larger collection of blood can create significant pressure and throbbing because the rigid nail plate leaves little room for swelling underneath it.
Color alone cannot reliably identify the cause of a dark toenail. A podiatrist may also consider how quickly the change appeared, whether there was a clear injury, whether the nail became thicker or brittle, and whether the surrounding skin is painful or inflamed.
| Possible cause | More typical clues | Recommended response |
|---|---|---|
| Subungual hematoma | Appears after running, hiking, impact, or shoe pressure. The area may be red, purple, brown, or black. | Reduce pressure and monitor the toe. Seek care for severe pain or extensive injury. |
| Toenail fungus | Usually develops gradually. The nail may become thick, brittle, crumbly, distorted, or lifted. | Have the nail examined. Testing may be appropriate before treatment. |
| Ingrown nail irritation | Pain, redness, or swelling is concentrated along one nail edge. | Avoid cutting into the corner. Arrange an evaluation if symptoms persist. |
| Bacterial infection | Increasing redness, warmth, swelling, drainage, odor, or worsening tenderness. | Seek timely medical evaluation. |
| Suspicious pigment change | A new or widening vertical band, pigment on nearby skin, nail splitting, or no clear injury. | Arrange a professional examination rather than assuming it is a bruise. |
Fungal nail changes commonly cause progressive thickening, brittleness, crumbling, distortion, or separation from the nail bed.
Learn about toenail fungus treatment →Pain and swelling along one edge can indicate irritation from an ingrown nail rather than blood beneath the center of the nail.
Learn about ingrown toenails →Treatment depends on the amount of discomfort, the extent of the injury, the stability of the nail, and whether another condition may be responsible for the discoloration.
Do not puncture the nail with a needle, burn a hole with a heated object, or place sharp tools beneath the nail. Home drainage can introduce infection, cause additional nail-bed damage, or overlook a fracture or deeper injury.
A bruised toenail does not always fall off. A small hematoma may grow forward with the nail while the nail plate remains attached. After a larger injury, the nail may gradually loosen because it has separated from part of the nail bed.
There is no single return-to-running rule for every bruised nail. Continuing modified activity may be reasonable when discoloration is limited, pain is minimal, the nail is stable, and the source of pressure has been corrected.
Many dark toenails that appear after clear sports-related trauma are bruises. Professional evaluation is appropriate when the pattern does not behave like an ordinary injury.
Melanoma beneath or around a nail is uncommon, and a dark nail does not automatically mean skin cancer. However, a new or changing vertical band, pigment spreading to nearby skin, nail lifting, splitting, or an unexplained growth should not be repeatedly treated as a bruise or fungal nail without an examination.
Illinois Foot & Ankle Clinic evaluates suspicious foot and nail changes and can determine when testing or referral is appropriate. Read more about the evaluation of possible skin cancer on the foot.
People with diabetes, neuropathy, poor circulation, or reduced sensation should use a lower threshold for seeking professional care. Reduced sensation may allow continued pressure on an injury without the person realizing that it is getting worse.
Patients with diabetes should not puncture, cut, or remove an injured nail at home. Learn more about professional care for diabetic foot concerns.
The goal of an examination is not simply to confirm that the nail is dark. The provider must determine why the change developed and whether the nail bed, surrounding skin, or bone has also been affected.
When the change appeared, what activity preceded it, and whether the problem has happened before.
Shoe length, toe-box depth, foot movement, lacing, and pressure points may be considered.
The nail plate, surrounding skin, tenderness, swelling, drainage, thickness, and pigment pattern are reviewed.
Nail sampling, imaging, referral, dermoscopic assessment, or biopsy may be considered depending on the findings.
Prevention requires more than simply buying a larger pair of shoes. The goal is to create sufficient room for the toes while keeping the foot stable enough that it does not repeatedly slide forward.
A dark toenail after a clear episode of running, hiking, or shoe pressure is commonly caused by trauma beneath the nail. The cause becomes less certain when there was no obvious trigger, the nail is gradually thickening, the surrounding skin is inflamed, or a pigment band is changing over time.
Do not rely on color alone. Consider how the change began, whether the nail hurts, whether its structure has changed, and whether the discolored area is growing forward with the nail.
Illinois Foot & Ankle Clinic can examine the nail and determine whether the change is consistent with trauma, fungal infection, an ingrown edge, infection, or another condition.
Your visit may include an examination of the nail and surrounding skin, footwear and activity review, testing when appropriate, and guidance about protecting the toe and returning to activity safely.
Repeated contact between the toe and the inside of the shoe can damage small blood vessels beneath the nail. Blood then collects under the nail plate and creates red, purple, brown, or black discoloration.
A bruise often appears relatively soon after running, hiking, impact, or repeated shoe pressure. Fungal changes usually develop more gradually and may cause thickening, crumbling, distortion, lifting, or involvement of multiple nails.
Not necessarily. A small bruise may grow forward with the nail. After a more extensive injury, the nail may gradually loosen or separate from the nail bed.
Modified activity may be possible when pain is minimal, the nail is stable, and the pressure source has been corrected. Stop or reduce activity if you are limping, pain is worsening, or redness, swelling, or drainage is developing.
Do not attempt to drain the nail yourself. A healthcare provider may use nail trephination when pressure and pain are significant. Home puncturing or burning can introduce infection and worsen nail-bed damage.
Arrange an examination if a streak appeared without a clear injury, becomes wider or darker, contains irregular colors, extends onto the surrounding skin, or does not appear to move forward as the nail grows.
Illinois Foot & Ankle Clinic
This article provides general health information and does not replace an examination by a qualified healthcare professional.
