I've had this problem for the past 4 years. My thumb would get hard/numb, then peel. This would last several weeks/1 month, then go back to normal (this cycle would repeat every several months/year).
In the past I've taken fungal medications including Nystatin, Lamisil, etc, and none had worked.
I finally just recently saw a dermatologist who said there was no evidence of any fungal infection, or any infection at all. He said it was a an allergic reaction to something I'm touching. He gave me cream, "Fluocinonide" and it started looking better in a day (and went back to normal within a week...when it would normally have taken at least 3 weeks at that point). He recommended getting a patch test done, where they would check to see what it is that I'm allergic to. It could be some sort of metal, or solvent etc.
Hopefully this helps. It had been a very frustrating problem for me, and now it looks like this is the solution.