hmm apple cider vinegar seems like it does quite a lot of helpful things related to removing human residue:

- can be used to clean shower caps
- removes hair product build-up
- dissolves flaky skin that can occur e.g. on the heels

vinegar of course is an acetic acid solution, and I was curious if there was any research on this, because acetic acid is some pretty nasty shit. first paper I've seen so far: sci-hub.tw/10.1111/j.1346-8138