A black toenail can be alarming at first glance. As shown in the image above, one of the toes displays a dark bluish-black discoloration beneath the nail plate, while the surrounding nails appear normal. This type of change is commonly associated with bleeding under the nail, but there can be several possible explanations. Understanding the causes, symptoms, and treatment options can help you determine whether it’s a minor issue or something that requires medical attention.

What Causes a Black Toenail?

The most common reason for a black toenail is a subungual hematoma, which is essentially a bruise under the nail. This usually happens after trauma to the toe. You may have dropped something heavy on it, stubbed your toe against furniture, or experienced repeated pressure from tight shoes during running or sports. Even if you don’t remember a specific injury, repetitive friction can cause small blood vessels under the nail to break and bleed.

When blood becomes trapped beneath the nail, it creates a dark red, purple, or black appearance. Over time, as the nail grows out, the discoloration gradually moves forward until it can be trimmed away.

Another possible cause is a fungal infection. In this case, the nail may not only turn darker but also become thickened, brittle, or crumbly. The discoloration from a fungal infection often starts as yellow or brown before turning darker in advanced stages.

In rare cases, a black streak or dark spot under the nail could signal subungual melanoma, a serious form of skin cancer. Unlike a bruise, this type of discoloration does not move as the nail grows and may spread to the surrounding skin.

Symptoms to Watch For

A black toenail caused by trauma is often painful at first. The pressure from trapped blood can create throbbing discomfort, especially within the first 24–48 hours after injury. Swelling and tenderness around the toe may also occur.

If the discoloration is due to infection, you might notice additional signs such as:

• Thickened or distorted nail shape

• Foul odor

• White or yellow streaks

• Crumbling edges

For more serious conditions, warning signs include:

• A dark line that widens over time

• Pigment extending onto the skin around the nail

• No history of injury

• Persistent pain without improvement

If you observe any of these red flags, it is important to consult a healthcare professional.

What Should You Do?

1. If It’s a Recent Injury

If the black toenail appeared after trauma and the pain is mild, you can usually treat it at home. Elevate your foot, apply a cold compress to reduce swelling, and rest the toe. Over-the-counter pain relievers may help with discomfort.

If the pain is severe and throbbing, a doctor may need to drain the trapped blood. This procedure is quick and can significantly relieve pressure.

Avoid attempting to puncture the nail yourself, as this can introduce infection.

2. If It’s Likely a Fungal Infection

Keep your feet clean and dry. Change socks regularly and wear breathable footwear. Over-the-counter antifungal creams or solutions may help, but stubborn infections often require prescription medication from a doctor.

Treatment can take several months because toenails grow slowly.

3. Monitor Nail Growth

In cases of bruising, the dark spot should gradually move forward as the nail grows. Toenails typically grow about 1–2 millimeters per month, meaning full replacement can take 9–12 months.

If the discoloration remains fixed in place or changes shape, seek medical advice.

Can the Nail Fall Off?

Yes, in some cases, the damaged nail may loosen and eventually fall off. This is common after significant trauma. A new nail will usually grow back, although it may take several months and may initially appear uneven.

Keep the area clean and protected if the nail detaches. Cover it with a sterile bandage and monitor for signs of infection such as redness, warmth, swelling, or pus.

When to See a Doctor

You should consult a healthcare provider if:

• Pain is severe or worsening

• There are signs of infection

• The discoloration appears without injury

• The dark area spreads or forms a streak

• You have diabetes or circulation problems

People with underlying health conditions should be especially cautious, as minor foot injuries can become more serious.

Prevention Tips

To reduce the risk of black toenails:

• Wear properly fitting shoes

• Trim nails straight across

• Use protective footwear during sports

• Maintain good foot hygiene

• Avoid prolonged pressure on toes

Final Thoughts

A black toenail is often the result of minor trauma and usually resolves on its own as the nail grows out. However, not all discoloration is harmless. Paying attention to accompanying symptoms and changes over time is key. When in doubt, it’s always safer to have a medical professional evaluate the condition.