Yellow toenails may be caused by ringworm of the nail, yellow nail syndrome and other diseases. 1. Tinea pedis: mainly related to fungal infections such as Trichophyton rubrum, Candida, Trichophyton mustelii, etc. Local blood circulation disorders and impaired immune function may also induce the disease. The patient’s nail plate may appear thickening, separation, atrophy, shedding and other symptoms, the nail color will also change, mainly manifested as white, dirty color, yellow and so on. 2. Yellow Nail Syndrome: the cause of the disease is still unclear and may be related to genetic factors. The patient’s limbs will have lymphedema, and at the same time, the fingernails or toenails may become discolored and soft, yellow or cracked. If yellowing of toenails occurs, it is recommended to go to a regular hospital to find out the cause.