Have you ever looked down at your feet and noticed that one of your toenails has suddenly turned black, dark purple, or brown? At first, you might assume it is simply a bruise or the result of wearing uncomfortable shoes. In many cases, that assumption is correct. However, a black toenail can sometimes indicate an underlying condition that deserves medical attention.
Toenails can reveal more about our health than we might realize. Their color, thickness, texture, and growth patterns can change for several reasons, including physical injuries, fungal infections, circulation problems, and certain medical conditions.
One of the most common explanations for a black toenail is a subungual hematoma, which occurs when blood collects underneath the nail after an injury. This can happen after stubbing a toe, dropping something heavy on the foot, or repeatedly wearing shoes that place pressure on the toes.
However, not every dark toenail is caused by trauma. Fungal infections, skin pigmentation changes, certain medications, and, rarely, melanoma can also produce dark discoloration.
The important thing is knowing which changes are likely to be harmless and which should never be ignored.
Here are the most important causes of black toenails, the warning signs to recognize, and what you should do to protect your nail and overall health.
1. A Bruise Under the Toenail: The Most Common Cause
One of the most frequent reasons a toenail turns black is bleeding underneath the nail.
Medically, this condition is called a subungual hematoma.
It develops when small blood vessels beneath the nail become damaged, allowing blood to collect between the nail plate and the underlying nail bed.
As the blood becomes trapped, the nail may appear dark red, purple, brown, or nearly black.
This can happen after several types of injuries, including:
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Stubbing your toe against furniture.
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Dropping a heavy object on your foot.
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Wearing tight shoes for extended periods.
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Running or walking long distances.
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Repeatedly hitting the front of the shoe during exercise.
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Participating in sports that involve sudden changes in direction.
Sometimes, the injury is obvious. In other situations, the person may not remember anything unusual happening.
For example, runners and hikers can develop dark toenails after repeatedly striking the front of their shoes during long periods of activity.
The big toe and second toe are particularly vulnerable because they often experience repeated pressure during walking and running.
What does a bruised toenail look like?
A subungual hematoma typically appears as a dark patch beneath the nail.
The discoloration may cover a small portion of the nail or extend across most of its surface.
Depending on the amount of bleeding, the nail may also become painful, swollen, or sensitive when pressure is applied.
In many cases, the dark area gradually moves toward the tip of the toe as the nail grows.
This movement is an important observation because toenails grow slowly. A bruise does not disappear immediately; instead, the damaged portion gradually grows outward.
What should you do?
If the injury is minor and the pain is mild, protecting the toe, avoiding tight footwear, and monitoring the nail may be sufficient.
However, severe throbbing pain, extensive bleeding, significant swelling, or a suspected fracture should be evaluated by a healthcare professional.
A clinician may sometimes drain trapped blood from beneath the nail to relieve pressure. This procedure is called trephination and should only be performed by an appropriately trained professional when indicated.
Do not attempt to drill, puncture, or burn a hole through the nail yourself. Doing so can cause burns, infection, or additional injury.
2. Repeated Pressure From Tight Shoes
Not every black toenail results from a single accident.
Sometimes, the cause is repeated pressure over weeks or months.
Shoes that are too short, narrow, or poorly fitted can repeatedly press the toes against the front or sides of the footwear.
This is particularly common among runners, hikers, football players, and people who spend many hours walking or standing.
When the toes repeatedly strike the inside of a shoe, tiny blood vessels beneath the nail may become damaged.
Small amounts of bleeding can accumulate, eventually producing a dark discoloration.
This is sometimes called a runner's toenail or jogger's toenail.
Common warning signs
People may notice:
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A dark purple or black area beneath the nail.
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Tenderness after exercise.
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Pain when wearing closed shoes.
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Repeated discoloration of the same toenail.
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A nail that gradually becomes loose.
The problem may affect one or several toenails, depending on footwear and activity.
How can you prevent it?
Choosing properly fitted shoes is one of the most important preventive measures.