A black spot on your toenail is almost always one of three things: a bruise from trauma, a fungal infection, or (rarely) a type of skin cancer called subungual melanoma. Each has a different treatment, so the first step is figuring out which one you’re dealing with. Most cases are simple bruises that resolve on their own as the nail grows out, but some require medical treatment.
What’s Causing the Black Spot
The most common cause is a subungual hematoma, which is blood trapped under the nail after an injury. You might remember stubbing your toe or dropping something on it, but repetitive pressure from tight shoes or running can also cause it without a single obvious event. The blood pools beneath the nail and appears as a dark red, purple, or black spot.
Fungal nail infections can also turn parts of the nail dark brown or black. These tend to develop gradually and come with other signs: the nail thickens, becomes brittle, and may lift away from the nail bed. The discoloration usually isn’t a clean, round spot but spreads unevenly across the nail.
Subungual melanoma is the least common cause but the most serious. It typically appears as a dark vertical streak or band running from the base of the nail to the tip, rather than a round spot. Key warning signs include a band wider than 3 mm with uneven borders, a streak that changes in size or shape over time, and pigment that spreads beyond the nail onto the surrounding skin (known as Hutchinson’s sign). This type of melanoma is more common in people with darker skin tones, where it can account for up to one-third of all melanoma cases.
How to Tell a Bruise From Something Serious
A bruised toenail will gradually move forward as your nail grows and eventually disappear off the end. Toenails grow at roughly 1.6 mm per month, so a spot near the base of the nail can take 9 to 12 months to fully grow out. If the dark area is clearly moving with the nail over time, that’s a strong sign it’s just trapped blood.
Be concerned if the dark mark doesn’t move with the nail, if it’s a vertical streak that stays fixed in place, or if the pigment extends onto the skin around the nail. A spot that grows wider or darker over weeks also warrants a visit to a dermatologist. When in doubt, take a photo of the spot every few weeks and compare. Movement toward the tip of the toe is reassuring. No movement is not.
Treating a Bruised Toenail
Small bruises that cover less than 25% of the nail and aren’t painful need no treatment at all. The blood will slowly reabsorb or grow out with the nail. You can apply ice wrapped in a cloth to reduce swelling and pain in the first day or two after the injury.
If the bruise covers more than 25% of the nail bed or the pressure is causing significant pain, a doctor can drain the trapped blood through a procedure called trephination. This involves creating a small hole in the nail to release the blood underneath. The most common method uses a heated instrument that melts through the nail. Once it reaches the blood pocket, the tip cools and stops, which prevents damage to the nail bed below. The relief is usually immediate. This procedure is only effective within the first few days after injury, before the blood begins to clot.
In cases where the bruise is very large, the entire nail may need to be removed to inspect and repair the nail bed underneath. This sounds dramatic but the nail regrows over several months.
Treating a Fungal Infection
Fungal toenail infections don’t resolve on their own and typically get worse without treatment. Over-the-counter antifungal creams and ointments are worth trying for mild cases, but they often struggle to penetrate the nail deeply enough to clear the infection entirely.
For persistent or severe infections, prescription oral antifungal medication is the standard treatment. You take the medication daily for 6 to 12 weeks, during which a new, healthy nail slowly grows in and replaces the infected portion. Because the toenail grows so slowly, it can take several months after finishing the medication before the nail looks fully normal again. These drugs can affect the liver, so your doctor will likely order blood tests during treatment to monitor for side effects.
A prescription antifungal nail polish is another option. You paint it on the infected nail and surrounding skin daily, wipe off the accumulated layers with alcohol once a week, and start fresh. This approach requires daily use for close to a year, which makes compliance a challenge, but it avoids the systemic side effects of oral medication.
Preventing Black Toenails
If you’re a runner or spend long hours on your feet, repetitive microtrauma to the toes is the usual culprit. The fix starts with shoe fit. Your toes need enough room in the toe box that they aren’t pressing against the front of the shoe with each step, but the shoe shouldn’t be so loose that your foot slides forward on downhill stretches. Getting fitted at a specialty running store, where staff assess your foot structure and gait, makes a real difference.
Lacing technique matters more than most people realize. Different patterns can redistribute pressure across the top of the foot, reducing the repetitive contact between your longest toes and the end of the shoe. If you notice black toenails after long runs, try loosening the laces near the toes while keeping the midfoot snug. Keeping toenails trimmed short and straight across also reduces the leverage that turns minor contact into a bruise.
For non-runners, the simplest prevention is wearing shoes that fit properly and being mindful of heavy objects around bare feet. Steel-toed boots are worth considering if you work in environments where things get dropped.