What should you know about green fungus under a nail?

Fungal nail disease often makes a nail thick, brittle, crumbly, or yellowish, while green staining can appear when moisture and bacteria collect beneath a lifted nail. These problems can occur together. Repeated wet exposure, tight footwear, nail injury, or an untreated foot infection can contribute. A clinician may examine several nails and the surrounding skin, and may test nail material before choosing treatment. Read about [Discoloured Nails](/symptoms/nail-discoloration/) and [Nail Fungus](/conditions/nail-fungus/) for background.

Keep the nail short, dry, and gently cleaned. Do not scrape underneath it, apply harsh chemicals, or cover persistent discoloration with polish. Change damp socks, let shoes dry, and check for peeling or itchy skin between the toes, which can accompany [Athlete's Foot](/conditions/athletes-foot/). A clinician may recommend [Topical Antifungal Treatment](/treatments/medical-dermatology/topical-antifungal-therapy/), [Oral Antifungal Treatment](/treatments/medical-dermatology/oral-antifungal-therapy/), laser treatment, or another approach after identifying the cause.

Arrange an assessment if the colour persists, the nail lifts or becomes painful, several nails change, or the skin around it becomes swollen. Seek prompt advice for spreading redness, drainage, fever, or difficulty walking. People with diabetes, poor circulation, or reduced immunity should not delay evaluation. [Nail Surgery](/treatments/surgical-dermatology/nail-surgery/) is reserved for selected problems rather than every discoloured nail.

Ask whether the colour is more consistent with fungus, bacteria, injury, or a mixed infection; whether testing is useful; how long treatment may take as the nail grows; and how to prevent recurrence in shoes and shared spaces.