Re: Germs, Germs, Germs ... for New Beginnings!
I think mommal is right on. Most of the world's dirt is not a big deal, just wash him up afterwards.
In the case of really gross things it is a good idea to have some really short, firm phrases that both you and any other caregiver use to communicate that you don't want him touching something. For us, we use "leave it" followed by a short explanation "yucky". We use the same phrase for all things that shouldn't be touched, so he knows that phrase well. "Leave it, hot" "Leave it, not for you" etc.
My little man was born 12/17/2010.
Baby girl was born 4/30/2014.