Gray nail is the common name for onychomycosis or nail fungus, which is mainly caused by dermatophytes. In addition, Candida and mold-like fungi (such as Aspergillus) can cause nail infections. The lesions often begin at the sides and ends of the nail plate, which gradually thickens and becomes brown or even black in color, with keratin and debris accumulating under the nail, causing the nail to loosen and the nail plate to separate. In some patients, the lesions start at the root of the nail and the nail becomes gray or brown, and some of them may fall off. In some cases, the whole nail is deformed and atrophied or missing. In some cases, the nail surface only appears as a white patchy cloudy area. The following conditions are prone to nail fungal disease: 1, suffering from ringworm and other dermatophytosis without timely treatment; 2, often wearing too tight, uncomfortable feet, impermeable shoes; 3, a history of nail trauma; 4, long-term use of corticosteroids or immunosuppressants; 5, immunocompromised patients such as diabetes. Treatment is usually topical antifungal medication, but should be adhered to until the new nail is completely grown out, and tinea capitis should be treated at the same time. If necessary, oral antifungal drugs can be used. Surgical nail extraction is feasible in cases of total nail disfigurement.