I'm not basing my argument on what could in theory happen, but rather on what appears to not to actually be a problem. Teenagers have bought sodium hydroxide a

I'm not basing my argument on what could in theory happen, but rather on what appears to not to actually be a problem. Teenagers have bought sodium hydroxide and hydrogen peroxide and heaven know what other nasty chemicals and plastered it in their own and their friends hair at home for decades, and there's no epidemic of permanent disfigurement from chemical burns (if there was, we'd have people up in arms over these chemicals being sold freely). In other words, the putative argument for requiring hair dressers licenses is solving a theoretical problem. Before you start doing business with someone, spend a few seconds evaluating the place. Maybe get a recommendation. If it's busy, that's a lot of other people vouching for it, it's probably at least OK. If it's a repurposed lemonade stand in a back alley, it's probably not (even in a jurisdiction that requires licenses!). It's really just basic common sense.