What should you know about brown nail fungus?

Fungal organisms can live in the nail plate or beneath it, gradually making the nail thicker, less transparent and easier to break. Debris may collect underneath, and the nail can separate from its bed. Athlete’s foot may occur at the same time because fungus can spread between nearby skin and nails. Brown colour is not specific: injury, staining, inflammatory nail disease and, rarely, a pigmented nail lesion can look similar. A clinician may inspect the nail and take clippings or scrapings for testing.

Keep nails short and dry, change damp socks, avoid sharing nail tools, and treat athlete’s foot if present. Do not cover a changing dark streak with polish before assessment. Depending on the nail, test result and medical history, treatment may involve topical antifungal treatment, oral antifungal treatment, laser treatment for nail fungus or nail surgery. Oral medicines can interact with other medicines, so a clinician should review your health and medication list. See Nail Fungus and Discoloured Nails for related guidance.

Arrange a review when discolouration persists, spreads, or comes with thickening, pain, lifting or crumbling. Seek prompt attention for a new dark band affecting one nail, pigment extending onto surrounding skin, bleeding, or a rapidly changing mark. People with diabetes, poor circulation or reduced immunity should seek advice early when a nail becomes painful or the surrounding skin is inflamed.

Ask whether a sample should confirm fungus, which nail is affected, how long treatment may take, and how improvement will be judged as the nail grows. Discuss liver health and medicine interactions before oral treatment, plus ways to reduce reinfection.