Gray toenails are usually caused by gray nails. Gray nails, also known as onychomycosis, is a fungal infection caused by the fungus Trichophyton rubrum, Trichophyton rubrum, Candida and certain molds. The initial appearance of gray nails is a lusterless gray spot on the lateral edge of the nail, which gradually turns yellowish brown to black. This is followed by cloudy, thickened, separated, atrophied, peeling nails, uneven surfaces, and hooked nails, which may lead to complications such as nail fungus. If a patient feels that their toenails are turning gray, they should promptly visit a hospital dermatologist for a fungal smear microscopy of the diseased nail and culture of the fungus. Once the diagnosis is clear, the doctor will usually choose an appropriate treatment plan according to the condition and the different causative organisms. Currently, oral terbinafine and itraconazole are recommended in clinical practice for antifungal treatment, and topical topical treatment such as terbinafine ointment and sertaconazole ointment can also be chosen. In case of distal nail plate involvement, macular striated nail, ingrown nail or nail plate thickness >2mm, removal of diseased nail or removal of diseased nail is required. In addition, laser treatment and photodynamic therapy can be used, which can inhibit pathogenic bacteria and kill microorganisms.