Grey nails are caused by fungal infection of the surface layer of the nail bed, and there are several reasons for the formation of this disease: 1. Women frequently do nail art in pursuit of beauty, using a nail contouring knife to remove all the protective layer on the surface of the nail, so that the nail plate’s defense against the outside world is reduced, and when the fungus in the air falls on the nail plate, it will proliferate and multiply on it, leading to grey nails; 2. Wearing shoes that are too thin, or walking in high heels will squeeze the toes. In serious cases, the nail and nail bed will separate, and then the fungus will enter the wound and cause gray nails; 3. Patients who have tinea pedis, due to incorrect treatment and improper care, cause the fungus to spread to the nail plate and multiply and form gray nails. Gray nails are contagious and can increase the number of their own gray nails and also infect other people through direct or indirect contact, so the patient’s household items should be separated from other people’s to prevent infection until they are cured.