I would say that barrier cream is a type of rash cream.

So diaper rash can be caused by a number of things. If it is caused by physical or chemical irritation, then the barrier stuff can work. The zinc oxide is basically just a thick goo that stays adhered to the skin so the bottom won't be rubbed raw by the diaper or chemically irritated by the poo or other stuff. You basically use it when there is a rash to let the skin have time to rebuild its natural barrier mechanisms. And there are different strength stuff. Like A&D or coconut oil can work for mild stuff. For medium just regular old butt paste zinc oxide. For the really bad rashes we'd use the extra thick zinc oxide. Most of the time we'd use nothing, but if he started getting a little raw we'd start with the light stuff and work our way up as appropriate.

Rash can also be fungal or bacterial...which you would use other stuff (I think this is the point he was making). To tell the difference on my kid, basically when the rash was on the outer surfaces it was more likely to be contact and when it was more in the crevasses it was more likely to be fungal (moist dark areas that fungi like). Fungal skin infections also kind of look the same (splotchy around the edges).

Not really familiar with bacterial stuff, but basically by the time you are working with fungal rashes that aren't working you should talk to a pediatrician so you can get an script for prescription strength anti-fungal stuff.

And then there are combo rashes. Sometimes you'd get rid of a bad fungal thing and be left with a nice chapped ass, and you have to transition over to the barrier stuff until it clears all the way. The fungal stuff is a cream or ointment that will provide some barrier, but not like zinc oxide. So it won't do the job if you have ulcerations or anything.