Food safety laws generally apply to most food you can touch with your hands at supermarkets - such as loose leaf spinach, bread rolls in the bakery, and anything at the deli. When handling these foods, you need to use tongs (or wear food safety gloves).
But mushrooms seem to be 'safe' for everyone to touch with their hands. There are never tongs near them (at least at any supermarket I've seen) and everyone uses their hands.
Why is this? What makes mushrooms special?