Borx is a natural mold retardant. If you live in an area where the humidity levels are high, try adding a cupful to your soapy water whenever you wash down the walls. I put mine in an old spray bottle & keep it in the shower to spray after each time it's used. Not only has it prevented mold build-up, it has removed those black spots that appear in the caulking. From the Reader's Digest book called 'Home Made Best Made'.