Why Is Your Toenail Brown? Why It Happens

A brown toenail is usually the result of one of a few specific things: a fungal infection, blood trapped under the nail after an injury, a dark spot from melanin, or staining from polish or shoes. The color itself is a symptom, not a diagnosis. What causes it depends on whether the discoloration appeared suddenly or slowly, whether it affects one nail or several, and whether the nail has changed in thickness or shape.

Why Is Your Toenail Brown?

Brown discoloration happens when something deposits pigment inside the nail plate or underneath it. The nail plate is made of keratin, the same protein in hair. It is slightly porous and can absorb pigment from fungus, blood breakdown products, or external dyes.

The most common cause is a fungal infection called onychomycosis. Certain fungi produce pigments as they digest keratin, and those pigments range from yellow to brown to nearly black. A second common cause is a subungual hematoma — blood trapped between the nail and the nail bed after a stubbed toe, a dropped object, or repeated pressure from tight shoes. As that blood ages, it darkens from red to purple to brown to black.

Less often, brown color comes from melanin. Melanocytes are pigment-producing cells that live in the nail matrix, the tissue at the base of the nail where new nail is made. When those cells become active, they can push melanin into the growing nail, producing a brown or black stripe or patch. This can be harmless. In rare cases it reflects a serious problem, which is why any new dark streak on a single nail deserves a medical look.

What Causes Brown Toenails Besides Fungus?

Fungus gets most of the attention, but it is not the only explanation. Several other causes produce a similar look, and telling them apart usually requires a clinician.

• Trauma — a single injury or years of pressure from shoes can break small blood vessels under the nail. The pooled blood stains the area brown as it breaks down.
• Melanonychia — melanin deposited in the nail plate. It often appears as a lengthwise stripe rather than a broad patch.
• Staining — dark nail polish, hair dye, self-tanners, and even some topical medications can seep into the nail plate and leave a brown tint.
• Psoriasis — this skin condition can affect the nails, causing pitting, separation, and a brownish or oily-looking discoloration.
• Lichen planus — an inflammatory condition that can damage the nail matrix and leave permanent changes, including brown color.
• Nutritional or systemic issues — in some cases, poor circulation, thyroid problems, or certain vitamin deficiencies have been associated with nail changes, though the evidence linking them specifically to brown color is limited.
• Medications — some drugs, including certain antibiotics and chemotherapy agents, are known to discolor nails.

One cause that deserves separate mention: a subungual melanoma. This is a rare form of skin cancer that grows under the nail. It can look like a brown or black streak, and it is the reason a new dark band on one nail — especially one that widens over time — should be evaluated rather than watched at home.

How Can You Tell Fungal Infection From a Bruise?

These two causes look similar but behave differently. A fungal infection typically develops slowly over weeks to months. It often starts at the tip or side of the nail and spreads toward the base. The nail may thicken, crumble at the edges, or separate from the nail bed. Several toenails may be affected, especially if the feet stay warm and damp.

A bruise, by contrast, usually follows a specific event you can remember — dropping something on your foot, kicking a piece of furniture, or wearing shoes that press on the toes. It often affects one nail. The discoloration may appear within days and then gradually grow out with the nail.

There is a useful physical clue. With a bruise, the discoloration sits under the nail and the nail itself stays smooth. With a fungal infection, the nail plate itself is often thickened, brittle, or distorted. That said, the two can occur together, and neither pattern is reliable enough to skip a professional evaluation when the cause is unclear.

One non-obvious point: a bruise does not always appear right after an injury. If bleeding happens slowly under the nail, the color may take days to show up, which can make the connection to the original event easy to miss.

When Should a Brown Toenail Worry You?

Most brown toenails are not dangerous. But certain features warrant a prompt medical visit because they can signal melanoma or another serious problem.

• A new dark stripe or band on a single nail, especially one that widens over time
• Discoloration that extends onto the skin around the nail, called Hutchinson’s sign
• A dark spot that does not grow out with the nail over several months
• Bleeding from under the nail without a clear injury
• A nail that lifts, cracks, or becomes painful without explanation
• Any new nail change in someone with a personal or family history of melanoma

Subungual melanoma is uncommon, but it is often diagnosed later than melanoma on other parts of the body because it is mistaken for a bruise or fungus. That delay matters. When in doubt, have it looked at.

How Is a Brown Toenail Diagnosed?

Diagnosis starts with a physical exam and a history. A clinician will ask when the discoloration appeared, whether there was an injury, and whether it has changed. They will look at the nail, the surrounding skin, and the other nails.

If fungus is suspected, a sample of nail clippings or debris may be sent to a lab. Testing matters because not every thick, discolored nail is fungal, and treatment for fungus is long and not always effective. Confirming the cause first avoids unnecessary treatment.

If melanoma is a concern, the clinician may take a small biopsy of the nail matrix. This is the only way to know for certain. Imaging is generally not useful for diagnosing nail conditions.

What Actually Helps a Brown Toenail?

What helps depends entirely on the cause, which is why identifying it comes first. There is no single remedy that works across all causes.

For a bruise, no treatment is usually needed. The discolored area grows out with the nail over several months. Toenails grow slowly — roughly 1 millimeter per month on average, though this varies by person and by toe. A nail that has been fully bruised may take a year or more to grow out completely.

For fungal infection, treatment typically involves oral antifungal medication, topical antifungal lacquer, or both. Oral treatment tends to be more effective than topical alone for moderate to severe cases, but it requires a prescription and monitoring because these drugs can affect the liver. Topical treatments work best for mild, early infections. Cure rates are not high, and recurrence is common, especially if the feet stay damp or the shoes are not treated.

For psoriasis or lichen planus, treatment focuses on the underlying condition, often with topical corticosteroids or other anti-inflammatory drugs. Nail changes from these conditions can be stubborn and may not fully reverse.

For staining, the fix is to stop the source. The stain grows out with the nail.

For suspected melanoma, the treatment is surgical removal, and the sooner the better.

No home remedy — vinegar soaks, tea tree oil, bleach, or hydrogen peroxide — has been shown in controlled trials to cure a fungal nail infection. Some of these can irritate the skin. If you want to try them, know that the evidence is weak and they are not a substitute for a confirmed diagnosis.

Can You Prevent Brown Toenails?

Some causes are preventable, others are not. Fungal infections are the most preventable. Keep feet clean and dry, wear breathable shoes, and change socks when they get damp. Do not share nail clippers or shoes with someone who has a fungal infection. If you use a public shower or locker room, wear sandals.

To reduce trauma, choose shoes with enough room in the toe box. Trim toenails straight across rather than rounding the corners, which can lead to ingrown nails and pressure. If you play sports that involve stopping and starting — running, tennis, soccer — you are more likely to develop repeated minor trauma under the nails.

Melanonychia and melanoma are not preventable through behavior. The best approach is awareness: check your nails periodically and see a clinician if something changes.

Does a Brown Toenail Always Mean Something Serious?

No. Most brown toenails are caused by fungus, trauma, or staining, none of which is dangerous. The concern is that a small number are caused by melanoma, and that cause cannot be ruled out by appearance alone. The practical takeaway is simple: if a brown toenail is new, changing, or unexplained, get it checked. If it is clearly a bruise from a known injury and it is growing out, you can usually watch it. When in doubt, ask a clinician.