I use athletes foot powder all the time, and have for years now. I haven't seen a problem, and never heard before that it could be.That doesn't mean it couldn't, we are always learning, and some chins are more sensitive than others.
Most of us will tell you if we find a problem with something we will discontinue, and what some have no problems with others might.
Maybe the one who said that believes it caused some problems for them.
I think your pretty safe using it and it does look like what I've seen around as fungus.
As this is pretty much the same as athletes feet the powder should cure it.