What causes yellow toenails?

The edge of the toenail yellow, may be the lack of a certain nutrition in the body, or is caused by a certain trace element, may also be caused by fungal infection caused by the nail yellow, this situation can go to the hospital to do an examination, check the specific cause of the disease, if the lack of trace elements on the supplement, if caused by fungal infection, the use of antifungal drugs for treatment.