Thick big toe nails may be caused by heredity, or considered to be the result of onychomycosis, psoriasis and other diseases. 1. Heredity: If congenital heredity leads to thick big toe nails and is not accompanied by other uncomfortable symptoms, it is generally a normal phenomenon and there is no need to worry too much. 2. Onychomycosis: Onychomycosis is mainly caused by dermatophyte infection, or considered to be induced by nail trauma, poor hygiene habits, low immunity and other factors. Patients may have symptoms such as cloudy nail plate, thickening, discoloration, buckling, uneven surface, etc., which is manifested as thick big toenails. 3. Psoriasis: the etiology of psoriasis is not yet clear, it may be due to the common role of heredity and environment. Or it may be caused by pathogen infection, obesity, smoking, skin injury, drugs and other factors. Patients may have symptoms such as hyperkeratosis of nails, nail clouding, and some patients may have thick big toenails. There are many reasons that lead to the patient’s big toenail thick, it is recommended that the patient go to the regular hospital, so as to clarify the cause of the disease and take treatment measures.