I don't know what chemicals are in this peppermint oil

My apologies, I thought I was being clear that I was referring to one of these bath mixes. I posted this before looking up what that exactly is. I've never used, seen, or heard of peppermint bath oils before, hence my saying

I imagine it's more than just peppermint

was not intended to imply that there must be other chemicals, only that if there were, there may be a byproduct from a reaction between it and the disinfectant used in the pool referred by /u/Cctbrkr. These disinfectant byproducts typically form when an organic material is added, though inorganics can also create DBP's.

The reason public facilities in the US are required to have signs and rules saying to shower before entering the pool is specifically to eliminate as many DBP producing agents as possible, some of which have been found to be cancerous.

but yes, obviously anyone who doesn't know the chemical break down of peppermint bath oil is obviously is in dire need of help.