What Do Longitudinal Brown Lines on Nails Mean?

A lengthwise brown or dark band may reflect pigment made in the nail unit, repeated injury, a mole-like change, medication effects or inflammation. Nail fungus more often causes thickening, crumbling or broader yellow, white or brown discoloration, while nail psoriasis can cause pitting, lifting or oil-like color changes.

Color alone cannot identify the cause. A clinician may examine the nail, surrounding skin and other nails, ask when the line began, and use magnification or photographs to compare change over time.

Take a clear photograph with the whole nail visible and note whether the band is widening, changing color or moving outward with nail growth. Avoid picking, aggressive filing and cosmetic products that hide the base of the nail before assessment.

Arrange a dermatology review for a new, persistent or changing band, especially when it affects one nail. Mention trauma, medicines, family history, skin changes and any signs of fungus or psoriasis. Do not start oral antifungal treatment without a diagnosis because it will not treat every cause of nail discoloration.

Seek prompt dermatology care if pigment spreads onto the surrounding skin, the band becomes wider or irregular, the nail splits, lifts or bleeds, or a dark mark appears suddenly without a clear injury. Pain, swelling or pus may indicate infection and also needs assessment.

Ask whether the pattern fits pigment, trauma, fungus or psoriasis, whether the nail should be photographed or tested, what changes to monitor, and whether any treatment is appropriate after the diagnosis is clear.