Black Toenail? Here's What It Means and What You Should Do

A dark toenail isn't always harmless—know when it's time to seek medical care.

A black toenail can be alarming the first time you notice it. While it is often caused by a minor injury, discoloration beneath the nail can sometimes signal an infection or, in rare cases, a more serious medical condition. Understanding the possible causes and knowing which warning signs require medical attention can help you protect your foot health and avoid unnecessary complications.

The Most Common Cause: A Bruised Toenail

The leading cause of a black toenail is a subungual hematoma, which occurs when blood collects beneath the nail after an injury. This can happen if you accidentally drop a heavy object on your foot, stub your toe, or repeatedly place pressure on the nail while running, hiking, or wearing tight-fitting shoes.

As blood becomes trapped beneath the nail, the toenail gradually turns dark purple, brown, or black. Over time, the discoloration slowly moves toward the tip of the nail as it grows out.

Typical symptoms include:

• Pain or throbbing shortly after the injury
• Tenderness when pressure is applied
• Dark discoloration beneath the nail
• Mild swelling around the toe

If the pain is severe because of pressure beneath the nail, a healthcare professional may be able to relieve it by draining the trapped blood.

Could It Be a Fungal Infection?

Not every black toenail is caused by trauma. A fungal infection may also darken the nail, although the discoloration often appears yellow, brown, or black over time.

Other signs of a fungal nail infection include:

• Thickened toenail
• Brittle or crumbly edges
• White or yellow streaks
• Distorted nail shape
• Unpleasant odor

Unlike a bruise, fungal infections usually develop gradually and often require antifungal treatment.

When a Black Toenail May Be More Serious

Although uncommon, persistent dark pigmentation beneath a toenail that does not follow an injury should always be evaluated by a healthcare professional. In rare cases, it can be associated with subungual melanoma, a type of skin cancer that develops under the nail.

Warning signs include:

• A dark streak or spot that gradually becomes larger
• Pigment extending onto the surrounding skin
• No history of trauma
• Persistent discoloration that does not grow out with the nail
• Changes in the nail without an obvious cause

These symptoms do not automatically mean cancer, but they should never be ignored.

What Should You Do?

If the black toenail developed after a recent injury and the pain is mild, you can often care for it at home by:

• Resting the foot
• Applying ice during the first 24–48 hours
• Elevating the foot
• Wearing comfortable shoes with plenty of toe room
• Taking over-the-counter pain medication if appropriate

Avoid trying to drill or puncture the nail yourself, as this can introduce infection.

If the discoloration appears without an injury, continues spreading, or is accompanied by severe pain, swelling, redness, drainage, or fever, seek medical attention promptly.

Can the Nail Fall Off?

Yes. After a significant injury, the damaged toenail may gradually loosen and eventually fall off as a new nail grows underneath. Complete regrowth usually takes 9 to 12 months, depending on the individual and which toenail is affected.

Keep the area clean and protected while the new nail grows, and watch for signs of infection such as increasing redness, swelling, warmth, or pus.

Prevention Tips

Many black toenails can be prevented by simple habits:

• Wear properly fitted footwear.
• Trim toenails straight across.
• Use protective shoes during sports or heavy work.
• Replace worn-out running shoes regularly.
• Treat fungal infections early before they worsen.

While most black toenails result from minor injuries and heal without lasting problems, persistent or unexplained nail discoloration should never be dismissed. If you're unsure of the cause, having it evaluated by a healthcare professional is the safest choice.