Dark nails usually come from one of a handful treatable causes: a bruise under the nail, fungal infection, staining from nail polish, or a nutritional deficiency. The fix depends entirely on what’s causing the discoloration, so identifying the source is the first step toward clearing it up. Most cases resolve on their own or with straightforward treatment, though a small number of dark nail changes deserve prompt medical attention.
Figure Out What’s Causing the Darkening
Nail discoloration falls into a few broad categories, and each one looks and behaves differently. A bruise under the nail (subungual hematoma) typically follows an injury, like stubbing your toe or slamming a finger in a door. It appears as a dark red, purple, or black spot that stays in one place and slowly migrates toward the tip as the nail grows out. You’ll usually remember the injury, and the spot may be tender at first.
Fungal infections tend to start at the tip or edge of the nail and work inward. The nail often thickens, becomes brittle, and may lift slightly from the nail bed. The color can range from yellow-brown to dark brown or black, and multiple nails can be affected at once.
Cosmetic staining from dark nail polish leaves a uniform yellow or orange-brown tint across the nail surface. It’s superficial and doesn’t affect the nail’s texture or thickness. Repeated nail trauma from biting, picking, or wearing tight shoes can also trigger dark streaks or patches over time. And vitamin B12 deficiency causes hyperpigmentation of the nails, hands, and feet, often alongside fatigue, numbness, or mouth sores. People with medium to dark skin tones are more likely to develop harmless pigmented bands in the nails as a normal genetic variation.
Treating a Bruised Nail
If you’ve bruised a nail, the main question is whether you need to do anything beyond waiting. For most uncomplicated bruises, conservative management is the standard approach: ice the finger or toe, keep it elevated, and take over-the-counter pain relief if needed. The dark blood under the nail will gradually grow out as the nail replaces itself.
If the pressure under the nail is causing significant throbbing pain, a doctor can perform a simple procedure called trephination, which involves creating a small hole in the nail plate to release the trapped blood. This provides near-immediate pain relief. More involved treatment, like removing the nail entirely, is only necessary when there’s an underlying fracture with displacement, a significant tear in the nail bed, or the nail has been pulled away from the fold at its base. For a straightforward bruise without those complications, leaving it alone works fine.
The waiting game is the hardest part. Fingernails grow at about 3.5 mm per month, so a bruise near the base of a fingernail can take three to six months to fully grow out. Toenails grow at roughly 1.6 mm per month, which means a bruised big toenail may take nine months to a year to look normal again.
Clearing a Fungal Infection
Nail fungus rarely clears up without treatment. If your nail is thickened, crumbly, and discolored, you’ll likely need either a topical antifungal applied directly to the nail or an oral antifungal medication prescribed by your doctor. Oral medications work from the inside out and are generally more effective for moderate to severe infections, though they require daily use for several months.
Topical treatments can work for milder cases. One small clinical study tested a daily application of an oil containing tea tree oil (a natural antifungal) on patients with mild to moderate nail fungus. After six months of treatment, 50% of patients had complete resolution, and another 43% showed significant improvement. By 12 months (including six months after stopping treatment), 78.5% had achieved a full cure. These results are promising for mild infections, but more severe cases typically need prescription-strength options.
Whichever route you take, patience is essential. Because the medication treats new nail growth while the damaged portion grows out, full visual clearing depends on how fast your nails grow. Expect at least three to four months for fingernails and closer to a year for toenails.
Preventing Reinfection
Fungal nail infections have a frustrating tendency to come back. The fungus can survive in old shoes and socks, creating a reservoir for reinfection. Discard or disinfect footwear you wore during the infection, and replace insoles at minimum. Wash socks in hot water, since fungal organisms have been shown to survive cold-water washing cycles. Keep your feet dry, change socks if they get damp, and wear sandals or shower shoes in public pools, gyms, and locker rooms.
Removing Nail Polish Stains
Surface staining from nail polish is purely cosmetic and sits on the top layer of the nail plate. Soaking your nails in lemon juice for about 15 minutes can lift most of the discoloration. Rinse, dry, and repeat the next day if any yellow tint remains. A paste of baking soda and a small amount of hydrogen peroxide, gently buffed across the nail surface with a soft brush, can also help. To prevent staining in the future, apply a clear base coat before using dark polish colors.
Correcting a Nutritional Deficiency
Vitamin B12 deficiency can darken your nails along with the skin on your hands and feet. This is more common in people who follow a strictly plant-based diet, those with absorption issues, and older adults. A blood test confirms the deficiency (levels below 200 pg/mL are considered deficient). Once B12 levels are restored through supplementation or increased dietary intake of animal products and fortified foods, the hyperpigmentation gradually reverses as new, healthy nail grows in. The timeline follows the same growth rates: a few months for fingernails, closer to a year for toenails.
When Dark Nails Need Urgent Attention
Most dark nails are harmless, but subungual melanoma, a type of skin cancer that develops under the nail, is the exception that matters. It’s rare, but catching it early dramatically improves outcomes. A set of guidelines known as the ABCDEF criteria can help you spot warning signs:
- Age and ancestry: most common between ages 50 and 70, and in people of African, Japanese, Chinese, or Native American descent
- Band: a brown or black streak wider than 3 mm with irregular or blurred borders
- Change: the streak is growing wider or changing color over weeks or months
- Digit: the thumb, big toe, and index finger are the highest-risk locations
- Extension: pigment spreading from the nail onto the surrounding skin (known as the Hutchinson sign), which is strongly associated with melanoma
- Family history: a personal or family history of melanoma
A key distinction: bruises under the nail migrate toward the tip as the nail grows and eventually disappear. Melanoma-related streaks tend to stay in place or widen over time, and they appear without any history of injury. If you notice a dark streak or band that you can’t explain with trauma, that changes in size, or that bleeds pigment into the skin around the nail, have it evaluated by a dermatologist promptly.