What should you know about subungual onychomycosis?

The infection often begins at the edge of the nail and moves beneath the plate. Debris can collect underneath, making the nail yellow, white or brown, thicker and harder to trim. It may become brittle, crumbly or separated from the nail bed. Athlete's foot can coexist because fungi may spread between skin and nails. A dark or altered nail has other possible causes, including injury and inflammatory nail disease, so a clinician may clip or scrape material for testing before prescribing treatment. See [Nail Fungus](/conditions/nail-fungus/), [Athlete's Foot](/conditions/athletes-foot/) and [Discoloured Nails](/symptoms/nail-discoloration/).

Keep feet or hands clean and dry, change damp socks, avoid sharing nail tools and treat associated athlete's foot. Topical antifungal treatment may suit limited disease but requires consistent application while healthy nail grows. Oral antifungal treatment can reach infection through the bloodstream and may require medication review or monitoring. Laser treatment is another option in some clinics, while nail surgery is reserved for selected cases. Treatment choice depends on the number of nails, involvement of the nail root, medical history and test result. Explore [Topical Antifungal Treatment](/treatments/medical-dermatology/topical-antifungal-therapy/) and [Oral Antifungal Treatment](/treatments/medical-dermatology/oral-antifungal-therapy/).

Arrange assessment when a nail remains thickened, discoloured or detached, particularly if several nails are affected or self-care has not helped. Seek prompt care for spreading redness, warmth, swelling, pus or fever around the nail. People with diabetes, reduced circulation or a weakened immune system should obtain medical advice early for foot or nail changes.

Should the nail be tested before treatment? Is the infection limited to the nail plate or involving the root? Which option fits my medicines and health history? How should I prevent reinfection?