A black toenail is almost always either a bruise under the nail (subungual hematoma) or a fungal infection, and the right treatment depends entirely on which one you’re dealing with. In most cases, a bruised toenail from trauma heals on its own as the nail grows out over several months. Fungal infections require medication. And in rare cases, dark pigmentation under the nail signals something more serious that needs prompt evaluation.
Identify the Cause First
Before you start treating a black toenail, you need to figure out why it turned black. The three main causes require very different approaches.
A subungual hematoma, or bruise under the nail, is the most common cause. It happens when blood pools between the nail and the nail bed after trauma. That trauma can be obvious, like stubbing your toe or dropping something on it, or subtle, like weeks of your toes hitting the front of tight shoes during running. The discoloration is typically painful at first and moves toward the tip of the toe as the nail grows out.
Fungal infections can also darken a toenail, though they usually start as yellow or white discoloration before progressing to brown or black. Fungal nails tend to thicken, become brittle, and sometimes smell. The key difference: fungal discoloration doesn’t migrate with the nail the way a bruise does.
Subungual melanoma is rare but serious. In about 65% of cases, it first appears as a dark vertical band running the length of the nail. These bands are often wider than 3 mm, with irregular borders and widening near the base of the nail. If the dark pigment extends beyond the nail onto the surrounding skin (called a Hutchinson sign), that raises additional concern. Unlike a bruise, melanoma pigmentation doesn’t move distally as the nail grows and isn’t linked to any injury you can recall.
Treating a Bruised Toenail at Home
If your black toenail came from a clear injury, like dropping a weight on your foot or a long hike in bad shoes, start with basic first aid. Apply ice wrapped in a cloth for 10 to 20 minutes at a time, repeating every hour or two for the first day. Elevate your foot above heart level when resting to reduce swelling and throbbing. Over-the-counter pain relievers can help manage discomfort in the first few days.
For mild hematomas where the pain is manageable and the nail is intact, no further treatment is needed. The bruise will slowly grow out with the nail. Toenails grow much more slowly than fingernails, so expect this process to take anywhere from 6 months to 2 years. A full toenail replacement averages about 18 months. During this time, keep the nail trimmed and the area clean to prevent any secondary infection.
When a Doctor Needs to Drain It
If the pressure under your nail is severe, with intense throbbing pain that doesn’t ease with icing and elevation, a doctor can perform a simple procedure called trephination. This involves creating a small hole in the nail to let the trapped blood escape, and it provides almost immediate pain relief.
This works best within 48 hours of the injury. A clinician will clean the toe with antiseptic solution, then use either a heated device or a needle to bore a tiny hole through the nail directly over the hematoma. The blood drains out, the pressure drops, and the nail is bandaged with sterile gauze. You’ll need to keep the area clean and dry afterward. The procedure sounds dramatic but is quick and typically not very painful since the nail itself has no nerve endings.
If the nail bed underneath is significantly torn, if there’s a fracture in the bone at the tip of the toe, or if the nail has been partially pulled away from the nail fold, more involved repair may be necessary. An X-ray can rule out a fracture if the injury was forceful.
Treating a Fungal Black Toenail
Fungal toenail infections don’t resolve on their own and almost always need medication. Topical treatments applied directly to the nail are an option for mild cases, but they have limited ability to penetrate a thickened nail plate. These medicated lacquers or solutions are typically applied daily for 24 to 48 weeks.
Oral antifungal medication is more effective for moderate to severe infections. The most commonly prescribed option is taken once daily for 12 weeks. Other oral antifungals may be prescribed for longer courses, sometimes 6 months or more for toenails. Your doctor will choose based on the type of fungus involved and your overall health, since oral antifungals can affect the liver.
Even with successful treatment, the nail won’t look normal right away. You’re waiting for the damaged nail to grow out completely and be replaced by healthy new growth, which takes 12 to 18 months for toenails. So even after the fungus is gone, cosmetic improvement is slow.
Signs That Need Prompt Medical Attention
Certain black toenails should not be treated at home. See a healthcare provider if you notice any of the following:
- No clear cause: The nail darkened without any injury or trauma you can recall.
- A dark vertical band: A streak running from the base to the tip of the nail, especially if it’s wider than 3 mm or has irregular borders.
- Pigment spreading beyond the nail: Dark coloring extending onto the skin around the nail fold.
- Signs of infection: Increasing redness, warmth, swelling, pus, or red streaks moving up the toe after an injury.
- Nail dystrophy without trauma: The nail is crumbling, splitting, or changing shape alongside the dark color.
Subungual melanoma is most common between ages 50 and 70 and occurs disproportionately in people of African, Asian, and Native American descent. It most often affects the big toe or thumb. In any case of suspicious pigmentation that can’t be explained by trauma, a biopsy is the only way to confirm or rule out melanoma. Early diagnosis matters significantly for outcomes.
Preventing Black Toenails
Runners and hikers are especially prone to black toenails from repetitive microtrauma. Your feet swell during extended activity as blood flow increases and impact forces accumulate, sometimes expanding up to a half size during a long run. That swelling pushes toes into the front of the shoe with every step.
Buy running shoes a half size larger than your regular shoes, and shop for them in the afternoon or evening when your feet are naturally at their largest. Leave at least a thumb’s width of space between your longest toe and the front of the shoe. If you have a longer second toe (Morton’s toe), pay attention to which nails take the most pressure, since it may not be the big toe.
The “heel lock” lacing technique, where you create an extra loop near the top eyelets to anchor your heel, reduces forward sliding inside the shoe. This is especially useful on downhill sections where gravity pulls your foot forward with each stride. Keeping toenails trimmed short also reduces the surface area that catches against the shoe. Moisture-wicking socks help prevent the combination of sweat and friction that contributes to both bruising and fungal growth.