Gray nails are the common name for onychomycosis, which is a part of nail fungus disease and is caused by fungus that invades the nail plate or nail bed. Onychomycosis is part of nail fungus, a nail disease that results from the invasion of the nail plate or nail bed by dermatophytes. The disease is contagious and can be caused by direct infection of the nail by tinea pedis, or by infection of the nail or toenail by trauma to the fungus. Poor hygiene of the hands and feet, wearing impermeable shoes and socks, and impaired immune function can increase the risk of onychomycosis. Ringworm of the nails has a slow course and can remain untreated and spread to others. Treatment of the condition is based on medications, and topical medications are usually ineffective because the nail plate is difficult to penetrate. It is often treated with oral medications such as itraconazole, fluconazole and terbinafine. Nail fungus should be timely consultation, the specific use of drugs need to follow the doctor’s instructions, nail fungus easy to recur, need to adhere to the treatment.