Gray nails, also known as onychomycosis, are finger (toe) nail infections caused mainly by fungi such as dermatophytes, yeasts, and non-dermatophytic mycobacteria. Tinea nail is contagious and can be transmitted directly or indirectly to others. The pathogenesis of onychomycosis is that dermatophytes invade the nail plate and release various enzymes to break down and destroy the nail plate, and because the nail plate lacks cellular immunity, it is generally susceptible to fungi and the nail plate is suitable for long-term survival of fungi, which in turn makes it susceptible to fungal infections. Tinea capitis is more likely to occur if the patient has a combination of diseases such as diabetes or tuberculosis that cause a decrease in immunity or if the patient uses medications such as immunosuppressants for a long time. It may also be caused by damage to the barrier function of the nail after trauma, combined with fungal infection. If the gray nail is transmitted by another person, the common source of infection is a patient with tinea corporis, ringworm, ringworm of the head, ringworm of the hands, and nail fungus caused by fungal infection. It is transmitted through direct contact, such as close contact with the lesions of a fungus-infected patient or your own ringworm-infected finger (toe) nails, and indirect contact, such as using towels and gloves contaminated with the causative fungus. Patients with onychomycosis need to pay attention to regular disinfection of personal items such as nail clippers, towels, gloves, socks, shoes, etc., and separate them from others, as well as separate basins and towels for their own use, as well as keep their shoes in the sun often to keep them locally dry.