There are many kinds of fungi that can cause gray nails, the most important of which is the fungus ringworm. This fungus lives all around us, in the soil, on the ground in baths and swimming pools, on animals (cats, dogs, pigs, etc.), and in the rashes of people with dermatophytosis. Gray nails, like other ringworm diseases, are most often found in hot and humid areas. In addition to geographical factors, personal circumstances determine who is more susceptible to the disease, such as lack of personal hygiene, frequent labor or exercise, love of non-breathable shoes, old age and frailty, etc. It is often the case that the person first develops a skin disease such as tinea pedis (ringworm) and then infects the toe (finger) nail. It is not only contagious, but can also be transmitted to others. In recent years, in addition to the traditional topical ointment form, there are some new nail coatings and oral antifungal drugs that have been introduced, which are highly effective and have few side effects on gray nails, and are more safe and reliable.