Don't know. I have them and spray sanitizer in them and the faucet before putting them on. However, when the outside of the faucet is wet from condensation, a seal forms, air compresses inside the faucet and pushes them off. Probably a rinse with sanitizer or water and air dry is enough. I have plenty of flies in my garage and did forget them once - poured a beer and had a fly in the pint.