Toenails simply yellow, may be a physiological phenomenon, with age, nails will become yellow and thickening, is a normal phenomenon, usually pay attention to trimming can be. It may also be caused by fungal infection, psoriasis, exogenous coloring and other reasons. 1. Fungal infection: the skin of the foot is infected by fungus, the color of nails will become yellow, which can cause onychomycosis or nail fungus disease, need to pass the fungus test, can further clarify the cause of the disease. 2. Psoriasis: psoriasis of the skin, can cause changes in the color of the toenails, the color of the nails will be yellow. 3. Exogenous coloring: the area of the toenails, the use of iodophor, potassium permanganate and other drugs can cause the nails to stain yellow. Causes of toenails simply turn yellow are more reasons, not clear the cause of the case, it is not recommended to arbitrary treatment, it is recommended that the hospital consultation, and timely cooperation with the doctor’s treatment.