What should you know about fungal melanonychia?

Melanonychia describes brown, grey, or black pigment appearing in the nail plate, often as a line or wider band running from the nail base towards the tip. Fungal infection can contribute to this appearance, especially when the nail is also thickened, brittle, crumbly, lifted from its bed, or surrounded by scaling skin.

Colour alone cannot identify the cause. A dark nail mark can also follow injury, medicines, skin conditions, or pigment-producing changes within the nail. A clinician may examine the nail and nearby skin, review its pattern and progression, and take a nail clipping or other sample when infection needs confirmation. A sample can help distinguish fungus from conditions that need a different evaluation.

Arrange a dermatology or primary-care assessment for a new pigmented nail band, particularly if the colour is changing or involves one nail. Keep nails clean and dry, change damp socks or gloves promptly, and avoid picking, scraping, or covering the nail with cosmetic products before assessment. Do not start oral antifungal medicine without a diagnosis, because treatment depends on the organism and on whether fungus is actually present.

If testing supports fungal infection, treatment may involve a prescribed nail medicine or another antifungal approach. Nails grow slowly, so the healthy part becomes visible gradually as the affected nail grows out. Follow the treatment instructions and attend any recommended review so the clinician can check the response.

Seek a prompt assessment if the band is widening, has uneven shades or edges, reaches the skin at the nail fold, or is accompanied by bleeding, persistent pain, swelling, or a nail that is lifting without a clear injury. These features do not establish a serious diagnosis, but they should not be attributed to fungus without examination. Seek urgent care for rapidly increasing redness, warmth, swelling, pus, or fever around the nail.

Ask: Could this colour change be caused by fungus or another condition? Does the nail need a clipping, scraping, or closer examination? Which treatment is suitable for this nail and how long should I use it? What change should prompt an earlier review? Mention any recent nail injury, medicines, skin rashes, or similar changes in other nails.