I've noticed some ostomy deodorants have DMDM hydantoin in them, which is a formaldehyde releaser. They put it in there to kill bacteria, but how safe could this be so close to a stoma and if you're a rinser? I think M9, in my experience, has been the safest and most effective.
I found one shampoo I was using had this in it as well and had class action lawsuits over it. Of course, I ditched it.
These days, we have to watch everything in our products. Like all of our products.