Black Toenail? Here’s What It May Mean — And What You Should Do

Noticing a black or dark toenail can be alarming, especially when it appears suddenly. While many cases are caused by minor injuries or pressure on the nail, doctors say some dark toenails may occasionally signal infections or more serious medical conditions.

Experts emphasize that understanding the possible causes may help people know when simple home care is enough — and when medical attention is necessary.

A Bruise Under the Nail Is One of the Most Common Causes

One of the most frequent reasons for a black toenail is a subungual hematoma, which occurs when blood becomes trapped under the nail after injury or repeated pressure.

This often happens because of:

• Tight shoes
• Running or sports
• Dropping heavy objects on the toe
• Repeated friction while walking

The trapped blood may turn the nail:

• Dark red
• Purple
• Brown
• Black

In many cases, the discoloration slowly grows out with the nail over time.

Fungal Infections May Also Darken the Nail

Doctors say certain fungal infections may cause toenails to become:

• Thickened
• Brittle
• Yellow, brown, or black
• Distorted in shape

Fungal infections often develop in warm, moist environments and may spread gradually if untreated.

People who frequently wear sweaty shoes or walk barefoot in public showers may face higher risk.

Sometimes It Could Signal Something More Serious

Although rare, experts warn that dark streaks or black discoloration under the nail may occasionally be linked to melanoma, a dangerous form of skin cancer.

Warning signs doctors pay attention to include:

• Dark lines spreading beyond the nail
• Color changes without injury
• Irregular pigmentation
• Nail destruction
• Bleeding or pain
• Changes that continue worsening

Persistent or unusual discoloration should always be evaluated by a medical professional.

What You Should Do If You Notice a Black Toenail

Doctors recommend:

• Monitoring the nail for changes
• Avoiding tight footwear
• Keeping feet clean and dry
• Resting injured toes
• Seeking medical care if pain becomes severe

Medical evaluation is especially important if:

• There was no clear injury
• The discoloration spreads
• The nail becomes painful
• Signs of infection appear
• The dark spot does not grow out normally

Can the Nail Fall Off?

In some injury-related cases, the damaged toenail may eventually loosen and fall off as a new nail grows underneath.

Doctors say this is fairly common after significant trauma, although regrowth may take several months.

The Bottom Line

A black toenail is often caused by bruising or pressure-related injury, especially among runners and active individuals. However, fungal infections and rare medical conditions may also be responsible.

Experts say persistent or unexplained nail discoloration should never be ignored, especially if it changes shape, spreads, or becomes painful.