Gray nails are medically called onychomycosis, an infection of the nail plate and under the nail by the skin fungus ringworm. Tinea versicolor gray nails are one of the more common types of nail disease in outpatient clinics. Basically, it accounts for more than half of the cases. It is more likely to involve toenails, which are four times more common than fingernails. It is particularly common in patients with nail disease who have a family history of the disease, and in those who have a low immune system, such as malnourished people, the elderly, and diabetics. The sharing of manicure tools, including slippers in public places, can lead to nail fungus. It feeds on the nail plate tissue, so it leads to changes in the normal structure of the nail. There are two main clinical manifestations of onychomycosis, one is fungal white nail and the other is subdermal onychomycosis, so some manifestations are a small spot on the nail plate, which gradually becomes larger and the nail plate becomes softer. There is also a small depression at the lateral and distal end of the nail plate, the horizontal hook of the nail, the nail plate will thicken and change color, after the infection will produce a lot of small flakes, the normal nail plate will change, looking vertically, there will be small flakes involved under the nail plate, the nail plate will buckle up, some will become concave some, in short, the normal shape of the nail plate will change. To confirm the diagnosis, you need to go to a regular hospital for fungal microscopy of onychomycosis according to the clinical manifestations and then treat it accordingly.