A friend used potassium permanganate solution to treat tinea on the hands/feet but after some initial success, the tinea seems to be making a comeback. Could the fungus develop resistance to potassium permanganate?
1.I dont' think a fungus would develop resistance to something so quickly.
2.As Chris suggested in the comments, it could be because "The desinfective effect is based on the production of reactive oxygen species. The problem is that the solutions used for this purposes are not very stable." So, if fresh solution haven't been used, it may be ineffective.