Black spot on toenail: causes and when to worry

What causes a black spot on a toenail?

A dark spot on or under a toenail can look alarming, but most have a simple cause. The shape of the mark, how it started and whether it moves as the nail grows are the best clues:

This table is a guide, not a diagnosis. A spot you can’t explain, or one that changes, is worth having checked.

Blood under the toenail (subungual hematoma)

Bleeding under the nail is by far the most common reason for a black spot on a toenail. Small blood vessels in the nail bed, the skin under the nail, break and the blood gets trapped under the hard nail. It can happen in two ways:

• A single injury, such as stubbing your toe, dropping something heavy on it, or having it stepped on. The toe usually hurts and throbs right away.
• Repeated pressure, often called runner’s toe. The toe keeps hitting the front or top of the shoe during running, hiking, tennis or a long day on your feet. This kind often doesn’t hurt much, so many people don’t remember an injury at all.

What it looks like as it heals

The spot usually starts red or purple and turns dark brown or black over a few days. Unlike a bruise on your skin, it doesn’t fade. The trapped blood stays under the nail and grows out with it.

Toenails grow slowly, roughly 1 to 1.5 millimeters a month. A small spot near the tip may be gone in a few months, while a spot near the base of a big toenail can take 12 to 18 months to reach the end. If a lot of blood collected, the nail may loosen and fall off, and a new nail grows in behind it.

How to treat blood under the toenail

For a small, painless spot, you don’t need to do anything except let it grow out and trim it away as it reaches the tip. For a fresh, painful injury:

1. Rest and raise your foot for the first day or two.
2. Ice the toe for 15 to 20 minutes at a time, with a cloth between the ice and your skin. Skip the ice if you have diabetes, numb feet or poor circulation.
3. Take an over-the-counter pain reliever if it’s safe for you.
4. Wear roomy or open-toe shoes so nothing presses on the nail.

If the toe is throbbing badly and the blood appeared within the last day or two, a doctor can release the pressure by making a tiny hole in the nail. This is quick and often brings fast relief. Don’t try it at home with a heated pin or a drill: you can burn the nail bed or cause an infection.

If the nail is loose, keep it trimmed short and covered with a bandage so it doesn’t catch on socks. Don’t pull it off. If you dropped something heavy on the toe or it’s very swollen, an X-ray can check for a broken bone. Our guide to taping a broken toe explains what to do if it is broken.

How to prevent black toenails from running and walking

• Leave about a thumb’s width of space between your longest toe and the end of the shoe.
• Make sure the toe box is deep enough that the top of the shoe doesn’t press on your nails.
• Lace your shoes so your heel stays locked in place and your foot doesn’t slide forward on downhills.
• Keep your toenails trimmed straight across and not too long.
• Wear moisture-wicking socks that don’t bunch up.

Runners who get black toenails again and again may find our runner’s guide to stronger feet helpful.

Black spot on a toenail with no pain or injury

A painless black spot on a toenail is very common, and there are several possible reasons:

• An old bruise you don’t remember. Pressure from shoes can cause bleeding under the nail without much pain. These spots move toward the tip over time.
• Small black dots or thin dark lines under the nail. These are usually tiny spots of dried blood from pressure or a knock.
• A fungal infection, especially if the nail is also thick, crumbly or discolored in other places.
• A pigment band, a brown or black stripe that runs the length of the nail.

Painless doesn’t always mean harmless. Melanoma under the nail is usually painless too, so a spot or streak with no injury to explain it should be watched closely and checked if it doesn’t grow out.

Can toenail fungus cause a black spot?

Yes, sometimes. Toenail fungus (onychomycosis) usually turns a nail yellow, white or brown, but some fungi and molds make it dark brown or black. A bacterium called Pseudomonas can also turn part of a nail green to black, usually where the nail has lifted and stays damp.

With an infection, the dark color usually comes with other changes:

• a thick, brittle or crumbly nail
• debris building up under the nail
• the nail lifting away from the skin underneath
• athlete’s foot on the nearby skin

A podiatrist can clip a small piece of the nail and send it to a lab to confirm the cause, since about half of abnormal-looking nails turn out not to be fungal. See our guide to toenail fungus treatment for the options that work.

Dark streaks and pigment bands

A brown or black stripe that runs from the cuticle to the tip of the nail is called longitudinal melanonychia. It happens when pigment cells in the nail matrix, the root at the base of the nail where the nail is made, add color to the growing nail. Common harmless causes include:

• Natural pigment. Bands are very common in people with brown or Black skin, often on several nails, and become more common with age.
• Friction or pressure, for example from shoes rubbing the same toe.
• A mole or freckle in the nail matrix.
• Some medicines, including certain chemotherapy drugs and a few others, such as minocycline and antimalarials, which can darken several nails.
• Pregnancy and some health conditions, such as low vitamin B12 or hormone disorders, which usually affect several nails at once.

Because a pigment band starts at the nail root, it doesn’t move forward as the nail grows. That’s the key difference from blood. Bands on several nails that have been stable for years are rarely a concern. A new band on a single nail in an adult should be checked, whatever your skin color.

Could a black spot on my toenail be melanoma?

Subungual melanoma, a melanoma that starts in the nail matrix, is rare. It’s most common on the big toe and the thumb, usually in adults, and it can happen in people of any skin color. It makes up a small share of melanomas overall, but a larger share in people with darker skin. Found early, it’s much easier to treat, which is why dark streaks deserve attention.

Warning signs to have checked:

• a brown or black streak in a single nail with no injury to explain it
• a streak that gets wider or darker over weeks or months
• a streak with blurry, uneven edges or several shades of brown and black
• pigment spreading onto the cuticle or the skin around the nail
• a dark mark that doesn’t move forward or grow out as the nail grows
• the nail splitting, bleeding, lifting or developing a lump underneath
• a personal or family history of melanoma

An injury doesn’t rule melanoma out. People often put a dark nail down to a knock they half remember, and a melanoma can sit under a nail for a long time before anyone checks it. If a “bruise” isn’t growing out, have it looked at.

If a doctor is concerned, they’ll look closely with a lighted magnifier (dermoscopy) and may recommend a biopsy, taking a small sample from the nail matrix. A biopsy is the only way to be sure. A podiatrist or dermatologist can do this or refer you to the right specialist.

How to tell a bruise from something more serious

Take a photo. It’s the simplest home check, and it gives your doctor a useful record:

1. Take a clear, close-up photo of the nail in good light, with a ruler or coin next to it for scale.
2. Note how far the spot is from the cuticle, the skin at the base of the nail.
3. Take another photo the same way after 4 to 6 weeks. Toenails grow slowly, so changes take a while to show.
4. Compare. Blood moves toward the tip, and a clear gap of normal nail appears behind it. A pigment band or melanoma stays attached to the cuticle and may widen.

Don’t wait for the photo check if the spot has any of the warning signs above. Book a visit instead.

How to treat a black spot on your toenail

Treatment depends on the cause, so there’s no single cream or remedy that removes a black spot:

• Blood under the nail: let it grow out and trim it as it reaches the tip. Painful, recent bleeding can be drained by a doctor.
• Fungal infection: prescription antifungal pills or nail solutions work best. Over-the-counter creams don’t get through the nail, and foot soaks soften and soothe but don’t cure it.
• Pigment band: usually watched with photos, with a biopsy if it changes or looks unusual.
• Melanoma: treated with surgery by a specialist team. The earlier it’s found, the simpler the treatment.

Nail polish hides a dark spot, but it also hides any changes. If you’re watching a spot, leave the nail bare between checks.

When to see a podiatrist about a black toenail

Get care the same day if:

• the toe is throbbing badly after an injury, or it looks bent or out of shape
• you have signs of infection: spreading redness, swelling, warmth, pus or a fever
• you have diabetes, neuropathy or poor circulation and have injured a toe

Book a visit soon if:

• a dark spot or streak appeared and you don’t remember an injury
• a streak is getting wider or darker, or pigment is spreading onto the skin
• the spot hasn’t moved forward after a month or two
• only one nail is affected and the mark doesn’t look like a bruise
• the nail is thick, crumbly or lifting, which suggests fungus

If you have diabetes, check your feet every day and have any nail change looked at promptly, since small problems can turn serious quickly. Learn more about diabetic foot care.

What to expect at your visit

A podiatrist will ask when you first noticed the spot, whether you injured the toe and what shoes you wear, then look closely at the nail and the skin around it. Depending on what they find, they may:

• trim the nail back to look underneath
• clip a sample to test for fungus
• take an X-ray after an injury (Evolve Health podiatrists have digital X-ray on site)
• recommend a biopsy, or refer you to a dermatologist, if a streak looks suspicious

Most black spots turn out to be old blood that simply needs time. If yours has no clear cause, or it’s changing, don’t wait to find out. You can read about nail care at Evolve Health, or find a podiatrist near you and book online.