Foot itch is caused by fungi and bacteria that live on your feet. In mild cases, they generally live on top of your skin and can be easily treated with many good over-the-counter products found at your local pharmacy.
However, with extreme foot itch, these fungi and bacteria may have penetrated a little deeper into your skin. They like to hide inside and underneath dead, calloused skin, making it difficult for other products to reach.
Most products work by killing surface fungi and bacteria. However, fungi and bacteria hiding inside and underneath dead skin, are left to reproduce, re-infect and come roaring back. This is called a flare-up.