i had the same thing on fingers for years.recently came across a medical journal written by GP who had same problem and found out that if you soak affected area in lemon juice-fresh or bottle juice and leave it air dry on skin.the blister will dry up and stop itchyness.I tried it once and ever since then i got it under control.even before you going to bed,try it and let your hand coat with lemon juice too!whenever it breaks out,i just do the same and it never lasted mroe than 2 days and never spread to other fingers since then.