Gray nails generally refers to onychomycosis, a nail lesion caused by dermatophytes invading the nail plate, for which both iodophor and tincture of iodine are effective. Povidone-iodine has a broad-spectrum bactericidal effect, can kill bacterial propagules, fungi, protozoa and some viruses. Povidone-iodine is effective in the treatment of onychomycosis. Tincture of iodine has a strong bactericidal effect on fungi, viruses and amoebae, compared to povidone-iodine, tincture of iodine has a better therapeutic effect on onychomycosis, but it is relatively more irritating to the skin, and can only be used on unbroken skin. However, it should be noted that tincture of iodine needs to be deiodized by alcohol before use. In addition, tincture of iodine can not be used on a large scale to avoid iodine poisoning. For patients with onychomycosis, it is recommended to go to the hospital, under the guidance of the doctor standardized treatment.