Dampness makes for scratches -- Your best defence against crud is to only put bone dry legs in or out. Great grooms never veer from this rule to live by.
This article details how and why.
Most medicated shampoos kill fungus but actually leave skin more prone to disease. If you want to gently and effectively kill the fungus and leave the skin more resilient, All-In-One Shampoo takes care of most skin issues in one bath: If already severe, this horse salve will break the cycle and Shampoo keep you out of the loop- as long as you dry the legs.