Dark toenails almost always come down to one of three things: a bruise under the nail, a fungal infection, or pigment changes from a health condition or medication. The fix depends entirely on the cause, and some causes resolve on their own while others need months of treatment. Here’s how to figure out what you’re dealing with and what to do about it.
Bruised Nails From Trauma
The most common reason for a dark toenail is a pool of blood trapped between the nail and the nail bed, called a subungual hematoma. This happens after obvious injuries like stubbing your toe or dropping something on it, but it also develops gradually from repetitive pressure. Runners, hikers, and people wearing tight shoes often notice a blackish-purple big toenail without remembering a single incident that caused it.
If the bruise is painful, a doctor can drain the blood by making a small hole in the nail. This relieves pressure almost immediately. If it doesn’t hurt, there’s no medical reason to drain it. The dark color simply grows out as the nail replaces itself, which takes up to 18 months for a big toenail. After trauma, regrowth can take anywhere from 6 months to 2 years. There’s no way to speed this up; you’re waiting for the entire nail plate to cycle out from the cuticle to the tip.
If the nail edges are cracked or lifted and there’s a deep cut underneath, the injury may need more than drainage. That situation calls for a visit to urgent care so a provider can check the nail bed for lacerations that need repair.
Fungal Infections
Fungal toenails typically start with white or yellow discoloration, then gradually darken to brown or black as the infection progresses. The nail also thickens, becomes brittle, and may separate from the nail bed. If your dark toenail came on slowly over weeks or months without an injury, fungus is the likely culprit.
Treatment depends on severity, and the options vary dramatically in effectiveness. Prescription oral antifungal medication taken daily for 12 weeks clears toenail fungus in 38% to 76% of cases. That’s the most effective option available. Prescription topical nail lacquer applied daily for 48 weeks, by contrast, has a cure rate of only 6% to 9%. The gap is enormous, which is why most dermatologists recommend oral treatment for anything beyond a very mild case.
Laser treatment is marketed heavily for nail fungus, but the results are mixed. Initial improvement is common, but a sustained cure has proven elusive even with multiple sessions. The fungus often returns, and outcomes depend on the type of laser used. It’s expensive, rarely covered by insurance, and not clearly better than oral medication.
Home Remedies
Apple cider vinegar soaks (equal parts vinegar and water, 30 minutes daily) and tea tree oil applied directly to the nail with a cotton swab are the two most popular home treatments. Both have antifungal properties in lab settings, but rigorous clinical evidence for their effectiveness on established toenail infections is limited. Tea tree oil appears to work better when combined with an antifungal medication rather than used alone. If you try these approaches, expect to wait several weeks before seeing any change, and know that they’re unlikely to clear a moderate or severe infection without prescription treatment.
Pigment Changes From Health Conditions
Dark streaks or bands running lengthwise through the nail can result from a surprisingly wide range of systemic causes. Vitamin B12 deficiency is one of the more common nutritional triggers. Hormone conditions like Addison’s disease, Cushing’s syndrome, and overactive thyroid can darken nails. So can autoimmune and inflammatory conditions including lupus, scleroderma, and psoriasis.
Certain medications are well-known culprits, particularly chemotherapy drugs, antiretroviral therapy for HIV, and antimalarial medications. Pregnancy can also cause temporary nail darkening due to hormonal shifts. In these cases, the discoloration often resolves once the underlying cause is treated or the medication is changed, though you’ll still need to wait for the affected nail to grow out completely.
When Dark Toenails Signal Melanoma
Melanoma can develop under a toenail, and it’s the one cause of a dark nail you don’t want to dismiss. It’s rare overall but accounts for up to one third of all melanoma cases in Black, Asian, and Native American populations. Peak incidence falls between ages 40 and 70.
The warning signs to watch for include a brown or black band wider than 3 millimeters with irregular or blurred borders, pigment that spreads beyond the nail onto the surrounding skin (a classic red flag called Hutchinson’s sign), and a dark streak that changes in width, color, or shape over time. A nail discoloration that doesn’t improve despite treatment for fungus or that doesn’t grow out the way a bruise should is also concerning. A personal or family history of melanoma raises your risk further.
The key distinction: bruises grow out with the nail and lighten over months. Fungal infections respond (even partially) to antifungals. A melanoma-related streak stays in place, originates from the base of the nail, and may gradually widen. If you notice any of these patterns, get it evaluated promptly. A biopsy is the only way to confirm or rule out melanoma.
Preventing Dark Toenails
Most preventable cases come from repetitive foot trauma, particularly in runners and people who spend long hours on their feet. Shoes with a roomy toe box are the single most important factor. Your toes shouldn’t touch the front of the shoe when you’re standing or walking downhill. Getting properly fitted at a specialty store matters more than any lacing trick.
That said, lacing techniques can help if your shoes fit well but your foot still slides forward. The runner’s loop method locks your heel in place: lace normally up to the second-to-last eyelet, then thread each lace straight up into the top eyelet on the same side to create a small loop. Cross each lace through the opposite loop, cinch them down, and tie as usual. This keeps your heel snug against the back of the shoe so your toes don’t slam forward with each stride.
If you’re dealing with a pressure point on the top of your foot that’s forcing you into looser shoes (which then causes toe bumping), window lacing can help. Unlace down to the eyelet just below the sore spot, thread straight up to the next eyelet instead of crossing, then resume normal crisscross lacing from there. This creates a gap in pressure right where you need it.
For fungal prevention, keep your feet dry, rotate your shoes so they can air out between wears, and wear moisture-wicking socks. Fungi thrive in warm, damp environments, and the inside of a sweaty shoe is ideal real estate. Trimming nails straight across and keeping them short also reduces the risk of debris and moisture getting trapped under the nail edge.
Realistic Timelines for Improvement
No matter the cause, dark toenails take a long time to look normal again. Even after successful fungal treatment, the discolored nail has to grow out completely before you see a clear, healthy nail. A full big toenail replacement takes an average of 18 months. Smaller toenails grow faster but still take many months.
For bruises, you’ll see the dark area slowly move toward the tip of the nail over several months before you can trim it away. For fungal infections treated with oral medication, the new nail growing in from the base should look clear, but the darkened portion ahead of it will be there until it reaches the end. For systemic causes, the timeline depends on when the underlying condition or medication exposure is addressed, plus the full nail growth cycle after that.