What should you know about a dark line on a nail?

A brown or black vertical band may reflect pigment produced in the nail, a small injury, or natural variation. Infection and inflammatory conditions can also alter nail colour, texture, or growth. Nail fungus more often brings thickening, crumbling, or yellow-white change, while nail psoriasis may bring pitting, lifting, or other surface changes, although appearances can overlap.

A single new line deserves attention if it widens, becomes irregular, changes colour, or extends onto the skin beside the nail. A photograph with the date can help show whether the band is moving outward with nail growth, but it cannot replace an examination.

Do not scrape, file, or paint over a changing line, and avoid picking at the cuticle. Note which nail is affected, when you noticed it, whether there was trauma, and whether the band is changing. Keep nails trimmed and dry, and do not start antifungal tablets based on colour alone.

A dermatologist may inspect the nail closely and decide whether testing is needed before treatment. If infection is confirmed, treatment may involve a prescribed topical option or oral antifungal treatment, depending on the organism, nail involvement, and your health history.

Arrange prompt dermatology review for a new or changing dark band, especially one that is widening, irregular, involves the surrounding skin, or affects one nail without a clear injury. Seek earlier care if there is bleeding, persistent pain, swelling, or nail separation. These features do not identify one diagnosis by themselves, but they should not be watched indefinitely.

Does the line appear to arise from the nail pigment-producing area or from an injury? Do I need a close examination, photograph monitoring, or a nail sample? Could fungus or psoriasis explain the texture? If treatment is needed, what monitoring is appropriate for the medicine?