Thanks for posting this link, @DeeAnna - very helpful. I was reviewing the IFRA for a FO my brother requested and it said 100% for Cat 9. I almost fell out of my chair. I think I’ll stick with what the Wise @TheGecko said and do 1oz PPO and see how that goes. FO is patchouli cedarwood from Natures Oil.The difference between the categories seems to depend on whether the product is normally applied to normal, unbroken skin or whether it's applied to irritated skin (shaving) or sensitive skin (underarm, gentialia) or is an aerosol product (cat 9).
I have more thoughts here -- IFRA guidelines | Soapy Stuff -- but I do agree the differences sometimes seem arbitrary to me too.