A black toenail is almost always a bruise under the nail, caused by blood pooling between the nail plate and the nail bed. Most cases heal on their own as the nail grows out, which takes 6 to 18 months for a toenail. What you need to do right now depends on how it happened, how much it hurts, and whether the nail is intact or coming loose.
Why Your Toenail Turned Black
The most common cause is trauma. You stubbed your toe, dropped something on it, or wore shoes that let your toes slam into the front with every step (common in runners and hikers). The impact ruptures tiny blood vessels under the nail, and blood collects in a dark red or black spot. The medical term is subungual hematoma.
Less commonly, a toenail turns dark because of a fungal infection. Fungal nails typically look thickened, chalky, or crumbly, and the discoloration tends to be yellow or brown rather than a sudden dark patch. In rare cases, a dark streak or spot under the nail can be subungual melanoma, a type of skin cancer. Melanoma under the nail often appears as a dark band running lengthwise, and pigment may spread onto the skin around the nail (called Hutchinson’s sign). A bruise from trauma will grow out with the nail over several months. A dark streak that doesn’t move or grow out warrants a visit to a dermatologist.
First Aid in the First 48 Hours
If you just injured your toe and the nail is turning dark, start with rest, ice, and elevation. Keep weight off the foot as much as possible for a few days. Apply ice with a thin cloth barrier for 10 to 20 minutes at a time, repeating every hour or two, but only within the first eight hours after the injury. Elevate your foot above heart level when sitting or lying down to reduce swelling and throbbing.
If the toe is swollen, you can wrap it lightly with a small elastic bandage, but don’t wrap it so tightly that you feel numbness or tingling. Over-the-counter pain relievers can help manage discomfort in the first couple of days.
When to Get the Blood Drained
If the pressure under the nail is intense and the pain is significant, a doctor or podiatrist can perform a simple procedure called nail trephination. They position a heated device, needle, or specialized tool over the center of the dark spot and apply gentle pressure to create a small hole through the hard nail plate only, not the tissue underneath. Blood drains out immediately, and the relief is often dramatic.
This procedure works best within the first day or two, while the blood is still liquid. It’s quick, usually done in a single office visit, and the nail itself stays in place. After drainage, keep the area clean and watch for signs of infection: redness spreading around the nail, swelling, pus, or fever. If any of those develop, or if the pain returns after initially improving, get it checked again.
What to Do if the Nail Loosens or Falls Off
A badly bruised toenail often separates from the nail bed as a new nail pushes up underneath it. This can happen weeks after the initial injury. If part of the nail is hanging off but still partially attached, gently trim away the loose portion rather than pulling it.
Clean the exposed nail bed with soap and water daily. Apply petroleum jelly to keep the area moist before covering it with gauze or a bandage. Don’t place adhesive tape or sticky bandages directly on the nail bed itself, as removing them will irritate the raw tissue. Instead, secure bandages to the surrounding skin, or use a loose elastic wrap for padding and protection. Keep this routine going daily until the area is no longer tender and new nail growth is visible.
A replacement toenail grows slowly. After injury, expect 6 months to 2 years for a full toenail to grow from the cuticle to the tip, with 12 to 18 months being typical. The new nail may look slightly ridged or uneven at first but usually normalizes over time.
If the Cause Is Fungal
A black toenail that wasn’t caused by an obvious injury, and that looks thick, crumbly, or cloudy, may be a fungal infection. Fungal nails can also separate from the nail bed, leaving visible space between the nail and the skin underneath.
Topical antifungal medications applied directly to the nail can help in mild cases, but they work best when combined with oral antifungal medication prescribed by a doctor. Oral treatment typically runs several months. Even after the fungus is eliminated, the discolored nail has to grow out completely before it looks normal again, which takes 12 to 18 months on average.
Preventing Black Toenails
Repetitive minor trauma is the most preventable cause. Shoes that are too short or too narrow let your toes hit the front of the shoe with every stride, and over time, this causes bruising under the nail. Runners, hikers, and people who spend long hours on their feet are especially prone.
When fitting shoes, leave a thumb’s width of space between your longest toe and the end of the shoe. Almost everyone has one foot slightly larger than the other, so fit to your bigger foot. Shop for shoes at the end of the day, when your feet are at their largest from natural swelling. Keeping toenails trimmed short and straight across also reduces the chance that the nail catches the shoe and takes repeated hits.
For downhill hiking or running, lacing techniques that lock the heel in place can prevent your foot from sliding forward in the shoe. If you consistently get black toenails during a specific activity despite good shoe fit, a half-size up in your athletic shoes is often the simplest fix.