There can be a number of reasons for itching at the bottom of feet. It can be because of a certain kind of soap or shower gel that you use. You can cure it by applying anti itch creams like Hydrocortizone and/or Diphenhydramine. However, it might also be because of Diabeties, low back, periferal neuropathy etc and you need to consult a doctor and get tested for these diesease.
