Gray nails are medically known as onychomycosis, which is contagious. Onychomycosis is a disease caused by dermatophytes that invade the nail plate or nail bed. The pathogenic fungus of onychomycosis mainly comes from the patient himself, onychomycosis is mostly spread by the patient himself who suffers from tinea pedis. Patients with tinea infection can act as a source of infection, spreading it directly or indirectly (contaminated home or public area environment) to close contacts, and therefore it is contagious. Therefore, it is necessary to pay attention to personal hygiene and reduce direct contact with patients with tinea pedis, tinea corporis, tinea cruris and tinea capitis. Avoid sharing slippers, bath towels, bedding and other items to prevent indirect transmission. Through health education, improve personal hygiene habits and enhance self-care awareness. Enhance disinfection and antibacterial of public environments such as bathhouses and swimming pools. If you are suffering from onychomycosis, please go to the hospital in time and standardize the medication under the doctor’s guidance.