Nail fungus, or nail fungus, is commonly known as gray nails, and it is caused by a fungal infection. The first is a fungal infection caused by foot fungus, which is a large fungal reservoir. If you have foot fungus for a long time and do not treat it actively, the fungus will gradually spread to the toenails, resulting in a change in the color of the toenails, thickening, debris under the nails, a dull surface, and unevenness, which means that gray nails are formed. The second reason is that after the nail is traumatized, the local tissue breaks down and the area becomes infected with fungus, which in turn affects the toenail and creates a destructive cuticle, leading to the formation of gray nails. So nail fungus is gray nails, they are caused by fungal infections, and once diagnosed, active antifungal treatment is required.