Yellowing of toenails can be seen in toenail staining, nail fungal disease, etc. 1. Physiological factors: in contact with certain chemicals such as dyes, picric acid or glutaraldehyde, etc., can make toenail staining yellow, can be mistaken for nail disease, attention to identification. 2. Nail fungal disease: mainly caused by dermatophyte infection, mostly spread by tinea pedis, the fungus on one side of the front edge and side edge of the invasion of the nail, can make the toenail thickening, become gray and yellow turbid, the surface of the nail can also have broken and uneven. Toenail yellowing and other abnormal manifestations, it is recommended to consult a doctor in a timely manner to identify the cause of the disease, the cause of the symptomatic treatment.