The common causes of yellowing toenails include physiological factors and pathological factors (including nail fungal disease, nail malnutrition, yellow nail syndrome, etc.). 1. Physiological factors: generally with age, the metabolism of the whole body slows down, toenails are also prone to aging, thickening, yellowing, which is a normal phenomenon, will not affect the health of the body. 2.Pathological factors (1) nail fungal disease: this disease is mainly caused by dermatophyte infection, followed by yeast and molds, usually nail fungal disease is mostly caused by tinea versicolor direct infection infection, and there are genetic factors, systemic diseases, local blood or lymphatic fluid reflux disorders, nail trauma and other diseases, the probability of nail fungal disease is higher. It manifests itself in symptoms such as hardening, thickening and yellowing of toenails. (2) Nail dystrophy:This disease is caused by a variety of factors, common causes include congenital nail deformity, hereditary nail dystrophy, skin diseases, drug factors, etc., resulting in nail plate loss of luster, yellowing, and there may be soft nails, thick nails, hooked nails and other symptoms. (3) yellow nail syndrome: the etiology of this disease is unknown, may be related to heredity, manifested as toenails become yellow, limbs have symptoms such as lymphedema. Excluding physiological factors, it is recommended that patients go to the dermatology department of regular hospitals in a timely manner, a clear diagnosis, and follow the doctor’s instructions for active treatment.