Vertical lines on the toenails may be caused by trauma, onychomycosis, and congenital white nail disease. 1. Trauma: If the toenail is damaged by external injury, it may lead to local cracks and vertical lines. 2. Onychomycosis: onychomycosis is mostly related to the invasion of the nail plate by dermatophytes, and it may be induced by trauma and lack of breathability of shoes, and the patient’s nails will appear cloudy, thickened, uneven and vertical lines and other symptoms. 3. Congenital white nail disease: this disease may be related to heredity, vitamin deficiency, metabolic disorders and other factors, the clinical manifestations of the nails appear dotted or thread-like stripes. There are different reasons for the vertical stripes on the toenails, so it is recommended that patients go to regular hospitals for relevant examinations to clarify the cause of the disease.