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Long-tail guide: brown or black nail discoloration

Brown or black toenail: fungus, blood, or melanoma?

A dark band on a nail is not a fungal diagnosis. Infection, injury, medicines, and nail melanoma can all produce the same appearance, and the difference is not something you can read off the color.

Quick answer

Does a brown or black nail mean fungus? No. Dark nail pigment is called melanonychia, and fungal infection is only one of many causes. A single nail with a band that is widening, or pigment that has spread onto the skin around the nail, should be examined by a clinician before you start any home routine.

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Last reviewed: September 30, 2026. Content is educational and should be checked against your own health situation.

Quick safety note

This guide is educational. It does not diagnose a nail condition or replace medical advice. A dark nail change deserves a professional opinion rather than a home routine, particularly if it involves one nail, is widening, or has appeared on the skin around the nail. Ask a qualified healthcare professional before starting a home routine if you have diabetes, poor circulation, thyroid disease, iodine allergy, immune suppression, pregnancy, breastfeeding, open skin, ulcers, or a painful nail.

What a dark nail band actually is

  • The nail plate is translucent keratin. It is not normally pigmented.
  • Pigment-producing cells sit quietly in the nail matrix, the tissue at the base where the nail is made.
  • When those cells are switched on, melanin is laid into the nail as it grows. The result is melanonychia: brown or black discoloration.
  • It can cover the whole nail, or appear as a lengthwise stripe. A stripe is called longitudinal melanonychia, and it is common and usually harmless.

What can cause it

Grouping the causes by mechanism is more useful than listing them, because it shows why the appearance cannot point at one answer.

Pigment switched on

  • Repeated pressure from footwear, or a single injury such as a stubbed toe.
  • Nail biting, picking, or habitual rubbing.
  • Pregnancy, and some prescription medicines.
  • Inflammatory skin conditions such as psoriasis and lichen planus.
  • Infection, including fungal nail infection and some bacteria.

More pigment cells

  • A mole or a lentigo in the nail matrix.
  • In a minority of cases, melanoma of the nail unit.

Pigment from outside

  • Hair dye, henna, nail polish, paint, and some topical products.

Trauma and infection are common. Melanoma is uncommon, but it is the one that must not be missed.

Why nail color cannot identify an organism

  • It is tempting to read a color as a clue to which organism is present. It is not a reliable clue.
  • Fungal nail infection can produce dark pigment, and it is not limited to molds. Dermatophytes and yeasts have both been described with pigmented nails.
  • Molds such as Aspergillus make pigments of their own, and nail infection with them has been described as greenish, black, or brown.
  • So a brown or black nail does not point at any one organism, and it does not even confirm that an infection is present.
  • A thick nail, a lifting nail, and dark pigment can each come from causes that have nothing to do with fungus.

The organism groups, and why the same appearance can come from several of them, are set out on fungal types and nail invasion.

Important: the only way to know what is in a nail is a laboratory test on a sample from that nail. Appearance, including color, is not a substitute.

Features that need a professional check

A practical frame for a pigmented nail is the ABCDEF list. The more of these that apply, the more reason to have the nail looked at.

  • A — Age and ancestry. Age roughly 50 to 70, or ancestry including African, Japanese, Chinese, or Native American.
  • B — Brown to black band. A band at least 3 mm wide, with a blurred or irregular edge.
  • C — Change. The band or the nail's shape is changing, or it has not responded to treatment.
  • D — Digit. The thumb, big toe, or index finger is most often involved.
  • E — Extension. Pigment has spread from the nail onto the skin around it, at the base or the sides.
  • F — Family or personal history. Melanoma, or atypical moles, in you or a close relative.

Alongside that list, these are also reasons to stop and get advice:

  • Only one nail is affected. Many nails at once is more often a benign pattern.
  • The nail plate is becoming deformed, cracking, or lifting away from the nail bed.
  • There is a lump under the nail, an ulcer, or bleeding without a clear injury.
  • The band is getting wider towards the base of the nail.
Do not rely on color to reassure you: up to half of nail melanomas have little or no dark pigment. A nail that does not look black can still be the one that needs attention.

What a clinician may do

  • Examine the nail with a dermatoscope, which shows detail the eye cannot.
  • Take a sample for microscopy and culture if an infection is suspected.
  • Biopsy the nail matrix if melanoma is a concern. That is the only way to confirm or exclude it.
  • Treat injury-related pigment by waiting, since it grows out with the nail.

Timing matters more here than in most nail questions. Nail melanoma is often found late, and its outlook is generally worse than melanoma at other sites, largely because the nail hides it.

Brown staining from iodine is a different thing

  • Iodine stains. A brown or orange-brown tint that appears after you apply iodine is expected, and it fades.
  • Iodine staining sits on or near the surface, usually follows where you applied it, and appears only after use.
  • A pigmented band that grows out from under the cuticle, or that was already there before you started, is not iodine staining.
  • If a stain and a pre-existing dark band are both present, the band is the part worth having examined.

Expected staining is covered separately in iodine stains toenails.

Common questions

Can nail fungus cause a brown or black nail?

Yes. Fungal nail infection can produce dark pigment, and it is not limited to molds. But injury, medicines, and other skin conditions cause the same appearance, so color alone cannot separate fungus from anything else.

Is a dark line on a toenail always melanoma?

No. Most lengthwise dark bands have a benign cause such as repeated pressure, a stubbed toe, or a mole. A single band that widens, or pigment that spreads onto the skin around the nail, needs a clinician rather than a home routine.

Should I start iodine on a dark nail?

Ask a clinician first if the change is dark, confined to one nail, and spreading. A topical routine cannot treat melanoma, and in that situation delay is the main risk.

More specific questions

When is home care the wrong choice? Is brown staining from iodine expected? How do different organisms invade a nail? Why are thick yellow nails harder? Are white nail patches easier to treat? Can iodine reach fungus under the nail?

Related nail fungus guides

Using iodine for toenail fungus? When to see a doctor instead Iodine, toenail fungus, and diabetes: safety questions first Iodine for toenail fungus: possible side effects and warning signs Iodine nail fungus before and after timeline: what to photograph

Sources consulted for this guide

  • DermNet: Melanonychia (nail pigmentation). dermnetnz.org — the overview of causes, including injury, medicines, inflammatory disease, and infection.
  • DermNet: Melanoma of the nail unit. dermnetnz.org — source of the warning-sign list and the ABCDEF frame used above.
  • DermNet: Fungal nail infections. dermnetnz.org — background on onychomycosis and how it is confirmed.
  • Benati E, Ribero S, Longo C, et al. Clinical and dermoscopic clues to differentiate pigmented nail bands: an International Dermoscopy Society study. Journal of the European Academy of Dermatology and Venereology 2016 — the clinical and dermoscopic features used to separate benign bands from melanoma.
  • A review of onychomycosis due to Aspergillus species. Mycopathologia review, NCBI — notes that mold nail infection may appear greenish, black, or brown, and that diagnosis needs microscopy plus repeated culture or molecular testing.

Evidence note: this guide is about when to seek care, not about treating a nail at home. Nail pigmentation has many causes, and only a clinician can examine the nail and, where needed, arrange a sample or a biopsy.