Toenails with horizontal lines may be related to a variety of factors such as onychomycosis, lichen planus, and nail trauma. 1. Tinea cruris is a skin disease formed when the toenail is infected with ringworm, which is mainly manifested in the foot clinic as thickening of the toenail, white spots on the toenail, and changes in the morphology of the toenail, such as vertical or horizontal stripes. 2. Nail lichen planus is a special type of lichen planus, which belongs to a kind of inflammatory skin disease with unknown etiology, and the clinical symptoms are mainly manifested as thickening of toenails, rough surface and unevenness. 3. Toenail trauma can cause damage to the nail bed and nail plate, so that the newborn nail plate morphology changes, which can be manifested as toenail deformation, bulging, thickening, as well as horizontal and vertical lines. Due to the variety of clinical manifestations and causes of the disease, it is necessary to ask the doctor for a face-to-face consultation.