Gray nails are known as onychomycosis and are primarily caused by a dermatophyte infection. Gray nails are nail lesions caused by dermatophytes that invade the nail bed or nail plate. Susceptibility factors include genetic factors, systemic diseases such as diabetes mellitus, localized blood and lymphatic fluid reflux disorders, nail trauma, or other nail diseases. Gray nails are mainly manifested by rough and thickened nails, gray and yellow turbidity, and uneven or broken surface of the nail plate. Gray nails can be treated with topical medication, first file the nail with a knife, then use 30% glacial acetic acid solution or 3%-5% iodine tincture twice a day until the new nail grows out, and can also be used systematically with drugs, such as itraconazole capsules and so on. If gray nails appear, you should consult your clinician and follow the doctor’s instructions.