A black toenail results from bleeding under the nail due to trauma. It often appears dark red, purple, or brown.12

1. Blunt Force Injury

Trauma to your toenail, like stubbing your toe, kicking something hard, or dropping a heavy object on your foot, can result in a black toenail. This injury, a subungual hematoma, is due to bruising under the nail, which appears black as it heals. It usually resolves on its own as the nail grows out.2

Contact a healthcare provider if you feel significant pressure or pain.3

2. Runner's Toe

Repetitive sports injuries often lead to black toenails. When your second or third toenails turn black, it might be "runner's toe." This happens if your nails are too long or your shoes don't fit well.2

In oversized shoes, your foot can slide forward, hitting the toe cap, especially downhill. Tight shoes can also pinch the nail, causing bleeding between the nail plate and nail bed.2

3. Malignant Melanoma

A more serious cause of black toenails is malignant melanoma, also called subungual melanoma. The term "subungual" refers to something that occurs beneath the nail. This condition is rare.2

Subungual melanoma is a dangerous form of skin cancer that can appear as a dark line running vertically along the nail's entire length.4

Early detection and treatment are crucial for melanoma. See a healthcare provider to rule out this cause of black toenail.2

What a Black Toenail Looks and Feels Like

Healthy toenails are usually strong, smooth, and uniform in color. When you have a black toenail caused by injury, you may experience:1

• Bleeding (hematoma)
• Brittle or loose nail
• Dark discoloration under the nail
• Pain or discomfort
• Swelling and bruising

How Are Black Toenails Diagnosed?

Your healthcare provider will ask about your symptoms and examine your feet, toes, and nails. They may inquire about potential causes like recent nail injuries, moisture exposure, or habits like frequent nail picking.4

They may also order:4

• Blood tests to assess for any other health conditions or infections
• Lab exam of nail samples or the nail matrix
• X-rays to evaluate the bone structure beneath the nail

What Are Effective Remedies for an Injured Toenail?

Treatment for a black toenail due to runner's toe or other minor injury usually involves:1

• Elevation
• Gentle compression
• Ice
• Rest
• Over-the-counter (OTC) pain medication

For more severe toenail injuries, your healthcare provider may recommend relieving pressure with a procedure called trephination. This procedure involves using a sharp instrument to puncture the nail, allowing the trapped blood to drain.1

In most toenail injury cases, your body will naturally reabsorb the hematoma, and the black nail will gradually grow out. This process typically takes approximately six to nine months.1

When To See a Healthcare Provider

Not all cases of black toenails require a visit to a healthcare provider. If you know the cause (such as an injury) and the discoloration affects less than 50% of the nail, you may be able to treat it at home.

See a healthcare provider if you don't know what's causing your black toenail, suspect your toe is broken, or you experience any of the following:21

• More than 50% of the nail is black
• Discoloration appears as a vertical line
• Bleeding that does not stop
• Intense pain
• Signs of infection, such as redness, discharge, or fever

If you notice darkening of the cuticle, it may be a sign of Hutchinson's sign. Seek immediate medical attention, as this could indicate a more aggressive form of melanoma.4

How To Prevent Toenail Injury

It can be difficult to prevent black toenails caused by accidental injury, but you can reduce your risk of toenail injury:

• Keep toenails trimmed and avoid sharp corners.
• Maintain good foot hygiene to prevent infections.
• Protect toes during sports with appropriate footwear.
• Wear properly fitted shoes, especially when running or doing aerobic activity.
• Wear protective footwear when doing home improvement projects or any construction work.