Horizontal stripes on nails may be caused by diseases such as lichen planus, psoriasis and onychomycosis. 1. Lichen planus: this disease may be related to heredity, viral infection, abnormal cell-mediated immune response, mental stress, smoking, influenza vaccination, etc. It may also be accompanied by dermatomyositis, scleroderma and other diseases. The patient’s nails will have longitudinal cracks, horizontal stripes, surface roughness and other damages, so the appearance of horizontal stripes on the nails may be caused by lichen planus. 2. Psoriasis: Research has shown that the current clinical belief is that this disease is the structure of the joint action of genetic and environmental factors, such as obesity, viral infections, bacterial infections, skin injuries, smoking and so on. Common symptoms include the presence of depression, separation, hyperkeratosis and other damage to the nails, which can be manifested as horizontal stripes on the nails. 3. Nail fungus: red trichophyton, candida, and trichophyton mustache are the causative organisms of this disease, which can be caused by the infection of tinea cruris and tinea pedis, and the common triggering factors are nail trauma, local lymph or blood circulation disorder, etc. Horizontal stripes on the nails is the typical symptom of tinea cruris, and it may also appear turbidity, thickening, warping, and peeling off. When horizontal stripes appear on the nails, patients need to go to the hospital for consultation to clarify the specific causes.