I had this really bad last year, I had to have four weeks off work and my feet were so blistered I could hardly walk. It came out of nowhere and I had never had it before. I was walking round in flip-flops with panty liners to absorb the ooze.
I saw two dermatologists who prescribed very strong steroids which I hardly used, god love them internet forums were my savior. For me after trial and error, twice a day wash feet dry well with hair dryer, pop blisters, aloe Vera gell, at first I did use a bit of steroid cream but not the really strong stuff, after that had sunk in Aveeno cream, cotton dressings, and bamboo socks. If you get deep skin cracks hydrocolloid gel sheets.
I had an allergy test and nothing really came up as a trigger. I have noticed that a pair of wellies started it off again with an odd blister, or it my feet get wet, but as long as I am on it so far it has cleared up.
The doctors kept asking me if I was allergic to anything apart from the odd rash from washing powder I am not, so the not really knowing what caused it makes me worried.