A black toenail is almost always one of three things: a bruise under the nail (subungual hematoma), a fungal infection, or, rarely, melanoma. The fix depends entirely on which one you’re dealing with, so the first step is figuring out the cause. Most black toenails from injury will resolve on their own as the nail grows out, but some need medical drainage, antifungal treatment, or further evaluation.
Identify the Cause First
The most common reason for a black toenail is trauma. You stubbed your toe, dropped something on it, or your running shoes let your toes slam against the front of the shoe over miles of repetitive impact. Blood pools under the nail, creating a dark blue, purple, or black discoloration. You’ll usually remember the injury, and the nail is often painful or throbbing, especially in the first day or two.
Fungal infections can also turn nails dark. Certain species of fungus produce black or dark brown pigment as they grow through the nail plate. A fungal black toenail tends to develop slowly, often alongside thickening, crumbling, or a yellowish edge. There’s typically no single moment of injury you can point to.
The most serious possibility is subungual melanoma, a type of skin cancer that grows under the nail. It’s uncommon but worth knowing about. Unlike a bruise, melanoma isn’t linked to an injury and isn’t painful. It often appears as a dark brown or black streak running lengthwise through the nail. One key warning sign is the Hutchinson sign, where dark pigment extends from under the nail onto the surrounding skin near the cuticle or nail fold. People between 50 and 70, and those of African, Japanese, Chinese, or Indigenous heritage, are at higher risk. If you see a dark band wider than 3 millimeters with an irregular border, or a streak that’s changing in size, get it evaluated promptly.
Home Care for a Bruised Toenail
If you’ve clearly injured the toe and the bruise covers less than half the nail, home care is usually enough. Wrap ice in a soft cloth and apply it to the toe to reduce swelling and pain. Elevate your foot when you can. The discoloration will stay put as the nail slowly carries the dried blood forward, eventually growing out and trimming off at the tip.
Toenails grow at about 1.6 millimeters per month, which is significantly slower than fingernails. A full replacement of a big toenail, from cuticle to tip, takes up to 18 months. That means a bruise near the base of the nail could take the better part of a year to disappear completely. It’s a slow process, but if the nail is intact and pain is manageable, there’s nothing else you need to do.
If your pain gets worse over the next few hours rather than gradually improving, that’s a sign the pressure under the nail is building and you should seek medical care rather than waiting it out.
When the Nail Needs Medical Drainage
A large, painful hematoma covering more than half the nail surface often needs to be drained. A doctor can relieve the pressure by making a small hole in the nail plate using a heated cautery device or a large-bore needle. The procedure, called trephination, releases the trapped blood and typically provides near-immediate pain relief.
Timing matters. This procedure works best within one to two days of the injury. After that, the blood clots and can no longer drain through a small hole. If you wait too long, a doctor may need to remove part or all of the nail to inspect and repair the nail bed underneath, particularly if there’s concern about a laceration beneath the nail.
Small hematomas that aren’t very painful, or ones that have already drained on their own from the edge of the nail, don’t require the procedure. You can let them grow out naturally.
Treating a Fungal Black Toenail
If fungus is the cause, the nail won’t fix itself without antifungal treatment. Oral antifungal medications are typically the first choice because they reach the infection through the bloodstream and work faster than topical options. Even so, expect treatment to take four months or longer to fully clear the infection.
A medicated nail polish is another option. It’s painted on the infected nail and surrounding skin once a day. After seven days, you wipe off the built-up layers with alcohol and start fresh. This approach requires daily application for close to a year, so it demands patience and consistency. Your doctor can help you decide between oral and topical treatment based on the severity of the infection and your overall health.
Regardless of the treatment method, the damaged portion of the nail still has to grow out completely before the toenail looks normal again. Since toenails grow so slowly, the cosmetic improvement lags behind the actual cure by months.
Signs of a Secondary Infection
A damaged toenail creates an opening for bacteria. Watch for these warning signs that a secondary infection has developed:
- Redness and warmth spreading around the nail fold or toe
- Increasing pain and swelling that worsens rather than improves over the first couple of days
- Pus buildup visible as a white or yellow pocket under or alongside the nail
If an abscess forms, it may need antibiotics or drainage. People with diabetes, poor circulation, or weakened immune systems should contact a provider at the first signs of infection rather than trying home remedies first.
Preventing Black Toenails
Runners and hikers get black toenails so often it’s sometimes called “runner’s toe.” The fix is almost always shoe fit. Your running shoes should have about a thumb’s width of space between your longest toe and the front of the shoe. That extra room accounts for the natural forward slide of your foot during downhill sections and the slight swelling that happens on long runs.
Your heel should sit snugly in the back of the shoe. A loose heel lets your foot slide forward with every stride, which is exactly what causes toes to bang against the front. If your toes feel cramped together or you can’t wiggle them freely, the shoe is too narrow. Lacing techniques that lock the heel in place, such as a runner’s loop near the top eyelet, can also help reduce forward movement inside the shoe.
Keeping toenails trimmed straight across and not too long removes another common trigger. A nail that extends past the tip of the toe catches on the shoe’s interior with every step. For non-athletes, simply wearing shoes that fit properly and protecting your feet during activities where heavy objects could fall on them covers most prevention.