Why Is My Toenail Black? 7 Causes & When to Worry

A black toenail is almost always caused by one of three things: trauma (blood pooling under the nail), a fungal infection, or—rarely—melanoma, a serious form of skin cancer that requires immediate medical evaluation.

The discoloration you're seeing happens because something has disrupted the normal pink nail bed underneath your toenail. In most cases, that "something" is blood from a minor injury you may not even remember—stubbing your toe, dropping something on it, or wearing shoes that are too tight during a long walk or run. Less commonly, the black, grey, or purple color signals a fungal infection that has progressed, or in rare instances, a melanoma growing beneath the nail. Understanding which cause applies to you determines whether you need a doctor today, next week, or not at all.

What Causes a Black Toenail? 7 Common Reasons in 2026

The color change under your nail is almost always blood, fungus, or pigment—and each has distinct visual and symptom patterns that help you identify what's happening.

Your toenail itself is a translucent keratin plate. It has no color of its own. What you see as "nail color" is actually the nail bed showing through. When that nail bed is healthy, it looks pink because of the blood flowing through tiny capillaries. When something goes wrong—bleeding, infection, or abnormal cell growth—the color shifts to black, purple, grey, or even white.

Did You Injure Your Toe Without Realizing It?

The most common cause of a black toenail is subungual hematoma—a fancy term for blood trapped between your nail and the nail bed. This happens when small blood vessels rupture after impact.

You might think, "I didn't hurt my toe," but these injuries are often subtle. Runners frequently develop black toenails from repetitive micro-trauma: the toe hitting the front of the shoe thousands of times over a long run. Hikers descending steep trails, soccer players, and anyone who drops something heavy on their foot can develop the same problem.

"Subungual hematoma is extremely common in athletes and typically resolves on its own as the nail grows out, though it may take 6 to 9 months for the discoloration to fully disappear." — Dr. Jane Andersen, DPM at the American Podiatric Medical Association

The key identifier: the black or dark purple area usually appears within 24–48 hours of the injury, and you can often remember (or figure out) when the trauma occurred.

Is Your Big Toenail Turning Black From Tight Shoes?

Your big toe takes the most pressure inside your shoe—it's the longest, and it bears significant force when you walk, run, or stand. Shoes that are too narrow, too short, or too tight compress the toe repeatedly, causing cumulative damage to the nail bed.

This is particularly common in:
- Runners training for long distances
- People who wear steel-toed work boots
- Anyone breaking in new shoes
- Hikers on multi-day trips

The discoloration typically starts at the tip or sides of the nail and gradually spreads. Unlike sudden trauma, shoe-related damage often appears days or weeks after the compression began.

Could Fungal Infection Be Turning My Toenail Black?

Fungal infections (onychomycosis) usually start with the nail turning white, yellow, or chalky. But as the infection progresses and debris accumulates under the nail, the color can darken to grey, greenish-black, or brownish-black.

Signs that fungus is the culprit:
- The nail is thick and crumbly, not just discolored
- There's a foul odor
- Multiple nails are affected
- The discoloration developed gradually over months
- You have athlete's foot between your toes

"Approximately 10% of the general population and up to 50% of adults over 70 have toenail fungus. Dark discoloration often indicates advanced infection requiring prescription treatment." — Dr. Shari Lipner, MD, PhD at Weill Cornell Medicine, dermatology specialist

Also Read: Why Is My Foot Red? 9 Causes & When to See a Doctor

Why Is My Toenail Black Underneath Only?

When the discoloration appears specifically underneath the nail—rather than on the surface—you're seeing pigment in the nail bed or matrix (the tissue that produces the nail). This presentation requires careful attention because it can indicate:

1. Subungual hematoma: Blood pooled under the nail from injury
2. Subungual melanoma: A rare but serious form of skin cancer
3. Bacterial infection: Pseudomonas bacteria can cause greenish-black discoloration

The distinguishing factors matter. Blood from trauma usually has clear edges and may show a reddish-purple hue. Melanoma tends to appear as a longitudinal streak running from the base to the tip of the nail, often with irregular borders.

What Does a Grey or Purple Toenail Mean?

Not all abnormal nail colors are truly black. Grey and purple tones often indicate different underlying causes:

Grey toenails often signal fungal infection in its mid-stages or nail psoriasis. Purple typically means recent bleeding. Blue-black can indicate older blood or, in some cases, circulation problems where the toe isn't getting enough oxygen.

Why Is My Toenail Thick and Black?

When your nail is both thickened and darkened, you're almost certainly dealing with one of two conditions:

Advanced fungal infection: The fungus invades the nail plate, causing it to become thick, brittle, and discolored. The nail may separate from the nail bed (onycholysis), and debris accumulates underneath, creating the dark appearance.

Repeated trauma over time: Chronic pressure or injury causes the nail to thicken as a protective response. This is common in runners, hikers, and people who work on their feet. The darkening comes from dried blood or damaged tissue beneath the thickened nail.

A thick, black nail that has been developing for months or years is unlikely to be melanoma, which tends to grow more rapidly and typically appears as a streak rather than affecting the whole nail.

When Is a Black Toenail Actually Melanoma?

Subungual melanoma is rare—it accounts for only 0.7% to 3.5% of all melanoma cases—but it's critical to recognize because early detection dramatically improves outcomes.

Warning signs that warrant immediate medical evaluation:

• A dark streak running lengthwise from the cuticle to the nail tip (called Hutchinson's sign)
• The pigment extending onto the skin around the nail
• A band of color that widens over time
• Only one nail is affected with no history of injury
• You're over 50 and the discoloration is new
• The nail has started to crack, bleed, or separate from the bed without trauma

Melanoma is more common in people with darker skin tones, where it often goes undiagnosed because the normal nail pigmentation can mask early signs.

How to Tell What's Causing Your Black Toenail

A careful look at the discoloration pattern, your recent activities, and accompanying symptoms usually reveals the cause—but when in doubt, see a podiatrist or dermatologist.

Ask yourself these diagnostic questions:

1. Did I injure this toe recently? (within the past few weeks)
2. Have I worn tight shoes, new shoes, or done unusual exercise?
3. Is the nail thick, crumbly, or separating from the bed?
4. Is there a distinct streak of color, or is the whole nail affected?
5. Is the dark area spreading or changing shape?

For most people, the answer points clearly to trauma or shoes. If the nail is thick and multiple nails are affected, fungus is the likely culprit. If there's a single streak on one nail with no injury history, a medical evaluation is essential.

Also Read: Why Is My Left Foot Itching? Spiritual Meaning & Causes

How to Treat a Black Toenail at Home

Most black toenails from trauma heal on their own as the nail grows out—but fungal infections require active treatment, and melanoma requires immediate professional care.

For Trauma-Related Discoloration

If you know the black color is from an injury:

1. Leave it alone if there's no pain or pressure. The discolored nail will grow out over 6–9 months.
2. See a doctor if there's intense pressure or throbbing. They can drain the blood with a small hole in the nail, providing immediate relief.
3. Protect the toe from further injury with properly fitting shoes.
4. Keep it clean and dry to prevent secondary infection.

For Fungal Infections

Mild fungal infections sometimes respond to over-the-counter treatments, but thick, black, advanced infections typically require prescription antifungals. Options include:

• Topical antifungal solutions (ciclopirox, efinaconazole) applied daily for 6–12 months
• Oral antifungal medications (terbinafine, itraconazole) taken for 3 months
• Laser treatment (newer option with mixed evidence)

Home remedies like tea tree oil or Vicks VapoRub may help mild cases but rarely clear advanced infections. The key is patience—nail fungus treatment takes months because you're waiting for a completely new, healthy nail to grow.

When You Need Professional Help

See a healthcare provider if:

• The discoloration appeared without any known injury
• There's a streak of color extending to the cuticle
• The nail or surrounding skin is bleeding
• You have diabetes or circulation problems
• The black area is expanding or changing
• Pain is severe or increasing
• Signs of infection appear (redness, swelling, pus, warmth)

For people with diabetes, even minor toenail problems require professional evaluation. Poor circulation and reduced sensation mean small issues can quickly become serious.

Preventing Black Toenails in the Future

The right shoe fit prevents most traumatic black toenails—leave a thumb's width of space between your longest toe and the shoe's end.

Practical prevention steps:

• Buy shoes in the afternoon when feet are slightly swollen
• Size up for athletic shoes, especially for running or hiking
• Keep toenails trimmed straight across, not rounded at corners
• Wear moisture-wicking socks to reduce friction and fungal risk
• Rotate shoes to let them dry completely between wears
• Use antifungal powder if you're prone to fungal infections

For athletes, proper lacing techniques can reduce toe pressure. Skipping the top eyelet and using a heel-lock lacing pattern keeps the foot anchored in the shoe, preventing it from sliding forward on descents.

Also Read: Why Is My Skin So Textured? 9 Causes & Fixes

In Short

A black toenail is usually harmless—most often caused by trauma from an injury or tight shoes—and will grow out on its own over several months. Fungal infections causing thick, black nails require treatment with antifungal medication. However, a dark streak on a single nail without injury history could signal melanoma and needs prompt medical evaluation. When in doubt about the cause, or if you have diabetes or circulation issues, see a podiatrist or dermatologist to rule out serious conditions.

What You Also May Want To Know

Why Is My Toe Black But My Nail Looks Normal?

When the skin of your toe is black but the nail appears normal, you're likely dealing with a circulation issue, bruising to the skin itself, or—in serious cases—tissue damage from lack of blood flow. Frostbite, peripheral vascular disease, and blood clots can all cause skin darkening without nail involvement. Unlike nail discoloration, black skin on the toe is a medical emergency if accompanied by numbness, coldness, or spreading darkness. See a doctor the same day.

Why Is My Toenail White Instead of Black?

A white toenail usually indicates superficial fungal infection, nail separation from the bed (onycholysis), or liver/kidney conditions in rare cases. White spots can also result from minor trauma to the nail matrix. Unlike black discoloration from blood, white areas don't contain pigment—they're either air pockets between the nail and bed, fungal damage to the nail surface, or circulation issues. Persistent whiteness across multiple nails warrants a medical checkup.

How Long Does It Take for a Black Toenail to Grow Out?

A black toenail from trauma typically takes 6 to 9 months to fully grow out and return to normal appearance. Toenails grow at approximately 1.6mm per month—much slower than fingernails. During this time, you'll see the dark area gradually move toward the tip of the nail as new, healthy nail grows in from the base. If the nail is severely damaged, it may fall off entirely and take 12–18 months to fully regrow.

Can I Exercise With a Black Toenail?

Yes, you can usually continue exercising with a black toenail from trauma, as long as there's no severe pain or signs of infection. However, you should address the underlying cause—typically ill-fitting shoes—to prevent worsening. If the nail is throbbing or feels like it's under pressure, a doctor can relieve this by draining the blood. For fungal black toenails, exercise is fine, but keep feet dry and wear moisture-wicking socks to avoid spreading the infection.

Should I Remove a Black Toenail Myself?

No, you should not forcibly remove a black toenail yourself. If the nail is loose and ready to separate naturally, you can gently trim the detached portions. But pulling off an attached nail risks infection, severe pain, and damage to the nail matrix—potentially causing permanent nail deformity. If the nail needs removal, a podiatrist can do it safely under local anesthesia, ensuring the nail bed is properly cleaned and protected.

Reviewed and Updated on May 11, 2026 by George Wright