Dark toenails almost always come down to one of three things: blood trapped under the nail from an injury, a fungal infection, or pigment changes from medications or other systemic causes. The fix depends entirely on which one you’re dealing with, and telling them apart is the first step toward getting your nail back to normal.
Figuring Out What Caused the Darkening
A bruise under the nail, called a subungual hematoma, usually appears suddenly after you stub your toe, drop something on it, or spend hours in tight shoes. The discoloration tends to be deep red, purple, or black, concentrated in one spot, and it’s often painful right away. Runners deal with this constantly from repetitive pressure against the toe box during long runs.
A fungal infection looks different. It typically starts at the tip or sides of the nail and spreads inward over weeks or months. The color leans yellow, brown, or chalky white rather than the deep purple-black of a bruise. You’ll also notice the nail getting thicker, crumbly, or misshapen over time, sometimes with a slight odor or debris buildup underneath. Fungal infections usually start in one nail before spreading to others.
Certain medications can also darken toenails without any injury or infection. Chemotherapy drugs are well-known culprits, with some platinum-based agents causing nail pigment changes in up to 70% of patients. Antiretroviral drugs, some anti-seizure medications, antimalarials, and even certain antipsychotics can do the same. If your nails darkened after starting a new medication, that’s likely the connection.
Treating a Bruise Under the Nail
If you just injured your toe and blood is pooling under the nail, start with the basics: ice it for 10 to 20 minutes at a time (with a cloth between the ice and your skin), and prop your foot up above heart level to reduce swelling. Over-the-counter pain relievers can help with the throbbing.
When the pressure under the nail is intense, a doctor can drain the blood through a small hole in the nail surface, a procedure called trephination. This works best within 24 to 48 hours of the injury and is only appropriate when the nail is still intact and attached. It provides almost immediate pain relief. If you wait too long or the nail is already lifting, drainage won’t help much.
For mild bruises, the dark spot simply needs to grow out. Toenails grow about 1.6 millimeters per month, which is roughly half the speed of fingernails. That means a bruise near the base of a big toenail can take 9 to 12 months to fully disappear. The discoloration will gradually shift toward the tip as the nail grows, and eventually you’ll trim it away. There’s no way to speed this up.
Watch for signs of infection as the nail heals: redness or swelling around the nail, pus-like drainage, fever, or pain that gets worse instead of better. These warrant a trip to the doctor.
Getting Rid of Toenail Fungus
Fungal toenail infections don’t resolve on their own, and over-the-counter topical treatments have limited success on their own for moderate to severe cases. The most effective approach is oral antifungal medication, typically taken daily for 6 to 12 weeks. Here’s the catch: even after you finish the pills, you won’t see a normal-looking nail for months. The medication kills the fungus, but the damaged nail still has to grow out completely and be replaced by healthy growth. Four months or longer is typical before the nail looks clear again.
Medicated nail lacquer is another option, applied like nail polish directly to the affected nail. It’s less invasive than oral medication, but the trade-off is time: you may need to apply it daily for close to a year. Your doctor can help you weigh convenience against effectiveness based on how severe the infection is.
For stubborn single-nail infections that don’t respond to medication, or when the diagnosis is uncertain, a doctor may recommend removing the nail entirely. This allows direct access to treat the nail bed underneath and lets a fresh nail grow in. Full regrowth takes many months given that slow 1.6 mm per month growth rate.
When Dark Nails Signal Something Serious
Most dark toenails are harmless, but a specific pattern of discoloration can signal melanoma under the nail. This is rare, but it’s the one cause you don’t want to miss. Warning signs include a dark band running lengthwise along the nail that gets wider over time, uneven or blotchy pigmentation within the band, and brown discoloration that bleeds into the skin around the nail (particularly the cuticle area or sides). The nail itself may also become distorted or damaged-looking.
The key distinction: a bruise stays the same size or moves forward as the nail grows. A melanoma-related band stays anchored in place, widens, and darkens. If you have a dark streak on your toenail that hasn’t changed in months, hasn’t grown out with the nail, or is spreading to surrounding skin, get it evaluated by a dermatologist. A biopsy of the nail bed can confirm or rule out melanoma.
Medication-Related Darkening
If a medication is behind your dark toenails, the discoloration usually fades on its own once the drug is stopped, though this can take 6 to 12 months depending on how long you were on it. Don’t stop any medication without talking to your prescriber first. In many cases, the nail changes are cosmetic and don’t require treatment, just patience while the pigmented nail grows out and gets replaced.
Preventing Dark Toenails From Recurring
Runners and anyone on their feet for long periods can take several steps to protect their nails. Proper shoe fit is the most important factor. Your toes need enough room in the toe box that they aren’t jamming against the front of the shoe with every step, but not so much room that your foot slides around. Getting professionally sized at a running store is worth it, especially since foot size can change over the years.
Moisture-wicking socks reduce the slipping and friction inside your shoe that leads to repeated micro-trauma. Adjusting your lacing can also help lock your foot in place so it doesn’t shift forward on downhill stretches. Silicone toe pads add a layer of cushioning that absorbs impact and protects the nail bed from pressure.
For fungal prevention, keep your feet dry, wear breathable shoes, and avoid walking barefoot in communal showers or pool areas. If you’ve had a fungal infection before, you’re more likely to get another one, so staying on top of these habits matters long-term.