Tinea pedis, also known as tinea pedis, is a fungal infection-like disease caused by dermatophyte infection of the skin of the feet. Gray nails refer to nail fungal disease caused by fungal infection of the nails of the hands, and if you switch to toenails, it refers to nail fungal disease caused by fungal infection of the toenails of the feet. So foot fungus and gray nails are both caused by fungal infections, but they are not the same problem. One is an infection of the skin of the foot, and the other is a nail fungal disease caused by an infection of the nails of the hands or toenails of the feet. Both are not a disease, although the infecting pathogens are both fungi.