Grey nails on the feet, also known as onychomycosis, are caused by fungal infections and are clinically divided into four main types, including white superficial type, distal lateral sub nail type, proximal sub nail type, and total nail destruction type, with different types and different initial symptoms, mainly covering the following aspects: 1. white superficial type: due to direct invasion of the fungus from the superficial layer of the nail plate, the superficial layer of the nail plate is dotted or irregular pieces of white turbidity, and the nail plate The surface of the nail plate loses its luster or is slightly uneven; 2, distal lateral sub nail type: this type is more common, the fungus from one side of the nail outline invade the distal front and side edges of the nail and make it thicken, grayish yellow cloudy, the surface of the nail plate is uneven or broken; 3, proximal sub nail type: usually these patients have low immunity, and the fungus from the proximal nail cortex invasion, the initial patient toe nail deck can appear white spots, at first only confined to the nail The initial symptoms are that the nail plate is no longer lustrous, thickened and deteriorated, and easily broken.