Brown Line in Toenail: Common Causes and Warning Signs

A brown line in a toenail can result from normal pigment, repeated pressure, injury, medication, or infection. However, a new, widening, irregular, or changing dark band deserves prompt medical assessment because, rarely, it can be a sign of melanoma under the nail.

What Does a Brown Line in a Toenail Mean?

A brown line in toenail is usually a narrow, lengthwise band that runs from the cuticle toward the tip. This pattern is often called longitudinal melanonychia. It happens when melanin, the pigment that gives skin and hair their color, is deposited in the growing nail plate.

Many brown nail bands are harmless, particularly when they have been stable for a long time, occur in more than one nail, or are related to natural pigmentation. Still, it is not possible to determine the cause reliably from color alone. A newly appearing, enlarging, uneven, or very dark line should be assessed by a qualified clinician.

The toenail grows slowly, so visible changes may persist for months. Looking at the whole pattern—including which nail is affected, whether the band is changing, and whether nearby skin is involved—provides more useful information than the color by itself.

Common Causes of Brown Nail Bands

Normal or increased melanin production is a frequent cause. Natural nail pigmentation is more common in people with darker skin tones and may affect several nails. It can also become more noticeable with age. In these situations, bands are often relatively even in color and width, although any new change should still be checked.

Repeated pressure or minor trauma can also affect toenails. Tight footwear, running, hiking, dancing, or a remembered injury may cause bleeding beneath the nail or stimulate pigment production. A bruise under the nail can look red-brown, purple, or nearly black. As the nail grows, the discolored area generally moves gradually toward the tip.

Other possible causes include inflammatory skin conditions, fungal nail disease, some medicines, nutritional factors, and benign pigment-producing growths in the nail matrix. Fungal infections more often cause thickening, crumbling, yellowing, or white discoloration than a clear single brown stripe, but appearances can overlap. Fungal nail infection can be evaluated when nail texture and color have changed together.

Less commonly, a dark band may be related to subungual melanoma, a form of melanoma that develops in the nail unit. This is uncommon, but early assessment matters because changes beneath a nail can be easy to overlook.

Features That Help Distinguish a Bruise From a Pigment Band

A bruise beneath the nail, also called a subungual hematoma, often follows a clear injury or repeated impact. It may be tender at first, and the discoloration is usually patchy rather than a consistently lengthwise stripe. Over time, it should move outward as the nail grows, leaving clearer nail behind near the cuticle.

A pigment band usually starts at the nail matrix, the tissue beneath the cuticle where the nail forms. Because new nail continues to grow from this area, the band may remain visible from the base of the nail to its tip. It may be light brown, dark brown, gray, or black.

It is sensible not to assume that a mark is only trauma because footwear pressure or a small injury is common. If the mark does not grow out, keeps becoming wider at the base, appears without an obvious explanation, or changes in appearance, a clinician should examine it rather than relying on home observation alone.

• More consistent with bruising: recent injury, early pain, a patch or blot rather than a neat band, and gradual movement toward the nail tip.
• More consistent with pigmentation: a lengthwise band that begins at the nail base and remains present as the nail grows.
• Needs assessment: new or evolving pigmentation, especially when only one nail is affected.

Signs That Need Closer Attention

Most nail discoloration is not melanoma, and a brown line does not by itself mean cancer. However, clinicians take certain patterns seriously because they may indicate an active change in the pigment-producing cells of the nail matrix. A dermatologist can assess these features with a close examination and dermoscopy, a magnified lighted device used to inspect skin and nails.

Features that warrant timely review include a band that is new in adulthood; becomes wider, darker, or more irregular; has several shades of brown, black, or gray; or is broader near the cuticle than near the tip. A band affecting one nail—particularly a thumb or big toenail—also merits attention when it is new or changing.

Pigment extending from the nail onto the surrounding cuticle or skin can be an important finding. Other concerns include nail splitting, lifting, distortion, a persistent lump beneath the nail, unexplained bleeding, or a sore that does not heal. These signs have causes other than melanoma, but they should not be ignored.

How a Brown Line in a Toenail Is Diagnosed

Diagnosis begins with a history and examination. The clinician may ask when the line first appeared, whether it has changed, whether there was trauma, which medicines are used, and whether there is a personal or family history of skin cancer. Examining all fingernails and toenails helps identify whether the pattern is isolated or part of more widespread pigmentation.

A dermatologist may use dermoscopy to examine the band’s color, lines, borders, and relationship to the nail folds. They may also compare photographs over time when a lesion appears low risk but requires monitoring. If fungal infection is suspected, nail clippings or scrapings may be sent for laboratory testing before treatment is recommended.

When there are concerning features or the diagnosis remains uncertain, a small biopsy of the nail matrix or nail bed may be advised. This is the only way to confirm or exclude melanoma definitively. Nail biopsy requires careful planning because the nail matrix is delicate and procedures should be performed by an experienced clinician.

Treatment and Nail Care

Treatment depends on the cause. A trauma-related bruise usually needs time to grow out, while reducing repeated pressure from footwear may help prevent further injury. A painful, fresh collection of blood under a nail may need urgent clinical drainage; people should not attempt to puncture or drain a nail at home because of the risk of infection and injury.

If testing confirms fungal disease, a clinician may recommend topical or oral antifungal treatment depending on the nail involved and the extent of infection. Dermatology assessment can help distinguish infection, inflammatory nail disease, trauma, and pigment changes so that treatment is directed appropriately.

Benign pigment bands may need no treatment beyond periodic review. If a biopsy identifies melanoma or another nail-unit tumor, care is planned according to the diagnosis and extent of disease. Management may involve dermatology, pathology, surgical specialists, and oncology teams. Melanoma treatment is individualized after proper diagnostic evaluation.

Until the cause is clear, it is helpful to avoid aggressive cuticle trimming, harsh nail chemicals, and repeated nail trauma. Keep toenails trimmed straight across, choose shoes with adequate toe room, and avoid covering a changing nail continuously with opaque polish, which can make monitoring more difficult.

When to Seek Medical Care

Arrange a medical appointment promptly for a new brown or black band in one toenail, particularly if it is getting wider, darker, or more uneven. It is also important to seek review if pigment reaches the surrounding skin, the nail becomes split or misshapen, or there is bleeding, pain, swelling, or a persistent sore.

Urgent assessment is appropriate after a significant toe injury when there is severe throbbing pain, a large dark area under the nail, an open wound, suspected fracture, or signs of infection such as increasing redness, warmth, pus, or fever. People with diabetes, reduced circulation, or immune suppression should contact a clinician early for new nail injuries or infections.

For a stable line that has been present for years without change, routine assessment can still provide reassurance and establish a baseline. Taking a clear photograph every few months in similar lighting, without nail polish, may help document change. Acibadem International’s multidisciplinary specialists and JCI-accredited hospitals can assess nail concerns and coordinate care for international patients when needed.

Frequently asked questions

Is a brown line in a toenail always melanoma?

No. Most brown nail lines have non-cancerous causes, including natural pigmentation, minor trauma, medicines, or benign changes in the nail matrix. However, melanoma under the nail can look similar, so a new or changing line should be evaluated rather than self-diagnosed.

Can tight shoes cause a brown line in a toenail?

Yes. Tight shoes and repeated impact can cause bruising beneath the nail or repeated minor trauma that affects nail pigmentation. A trauma-related mark should gradually grow toward the nail tip as the nail grows, but persistent or changing discoloration should be checked.

How long does it take for a toenail bruise to grow out?

Toenails grow slowly, so a bruise may take many months to fully grow out. The dark area should gradually move away from the cuticle toward the nail tip. If it stays fixed at the nail base or changes shape or color, medical assessment is advisable.

What is longitudinal melanonychia?

Longitudinal melanonychia is the medical term for a brown, gray, or black band running lengthwise along a nail. It reflects pigment in the nail plate and can be harmless, but the cause should be assessed when the band is new, isolated, or changing.

Should nail polish be removed before a nail examination?

Yes. Removing nail polish, gel products, and artificial nails before an appointment allows the clinician to see the full nail and surrounding skin. Avoid trying to scrape, file deeply, or cut into the affected area before the examination.

Which doctor should assess a dark line under a toenail?

A dermatologist is often the most appropriate specialist because they evaluate pigmented skin and nail changes and can use dermoscopy or arrange a biopsy when needed. A primary care clinician or podiatrist can also assess the problem and refer to dermatology if there are concerning features.

References

• American Academy of Dermatology
• American Cancer Society
• National Cancer Institute
• DermNet
• British Association of Dermatologists

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.