Fungal. Any type of fungal cream either by prescription or over the counter.
Try this. Make sure your feet are as dry as possible. Powder would help absorb perspiration. Another thing that can help is a prescription called drysol applied at bed time. Even under arm antiperspirant sprays containing aluminum chloride used on the feet can help. I also recommend socks made of more cotton or wool rather than synthetics such as nylon or polyester. Otc medications: lotrimin, (clotrimazole) cortisone.
See a dermatologist. Begin with exam and diagnosis. You probably need a prescription.
See a podiatrist. Could be fungal or dermatoses.
See a doctor. If you have tried several over the counter preparations and still have a problem you need to consult a doctor.