A rash on the foot can have a variety of causes. It may be a form of eczema, which is usually very itchy. It also may be an allergic reaction to something with which your feet have come into contact, such as materials in your shoe or poison ivy. Another common reason for a foot rash is athlete’s foot, which is caused by a fungal infection. Only by having the rash examined will you be able to get a precise diagnosis. A foot and ankle surgeon will determine the cause of your rash and provide appropriate treatment.