Cracks in toenails may be caused by trauma, onychomycosis and psoriasis. 1. Trauma: If the local area suffers from collision, pressure and other trauma, it may lead to cracks in the patient’s toenails. 2. Onychomycosis: the etiology is mostly related to pathogenic bacterial infections, such as red trichophyton, bearded trichophyton and so on. Patients will have symptoms such as cloudy nail plate, separation, discoloration and cracks. 3. Psoriasis: the cause of the disease is not clear for the time being, it may be related to heredity, environment and infection, etc. Patients will have symptoms such as itchy skin, pitting of nails, etc., and cracks may appear on the toenails of some patients. There are many reasons for cracked toenails, and patients are advised to seek medical examination to clarify the causes.