First, I would see a podiatrist. I have done a Google search on it, and folks that have this usually have seen a doctor to rule out anything serious. One comment I noticed was that it could be foot rot. You can't pass it on or catch it, it runs in your family, normally the males. The article went on to say to wear only leather shoes no trainers unless training. Change socks regularly only wear shoes for one 24hr period and then use a new pair and rotate them.
As I said, however, I would find out for sure what it is, a GP or foot specialist would be your best choices.