you never spent 1 hour with someone's dirty sweaty body on you either (sex doesn't count)
if you think i'm bullshitting, just ask whoever teaches the jiu jitsu
like i mentioned before, ringworm is so popular with grappling arts, that trainers and students take hygiene pretty seriously. if you have ringworm, you can't train and that's a waste of money. If you're promoting ringworm and dirty habits by having a stinky ass belt, you won't find people willing to roll with u. in fact, you may get sent out.
it's simple science tho...all that rubbing and grinding on the skin, makes it more susceptible to infections. make sure they wipe their mats and clean their showers frequently also. that's the first thing I did before training.