He won't be the first -- or the last -- one to tell you that! LOL
I'm allergic to most soaps, but I can use Kiss My Face brand olive oil soap. (It's supposedly the chemically extracted coconut oil that's used in most soaps that causes the problems; cold-pressed coconut oil is the good stuff, but I digress....) I need to check to see if they make a liquid soap. I've made my own before, but it'd be easier if I could just buy it. I want to try adding peppermint oil to it!
If you can use castile soap (I can't), I know you can buy a castile soap concentrate that has natural peppermint oil in it.
Ouch, allergy to coconut oil would be a problem with soaps. Have you looked for a Calendula (marigold) liquid soap?