Don't know about jock itch, but I unknowingly stuck my hand in a batch of very concentrated starsan and it ended up peeling the skin right off my whole hand. Looked like a very bad sunburn, but luckily it didn't hurt.
That's what happens when you try to mix up some starsan after a night of scotch drinking. Measured out the 1/2 oz or so of the acid on the left side, but opened the right cap and dumped half of the starsan bottle into a gallon or so of water.