Living tissue on your hands already contains a plethora of germs and more pathogen organisms get picked up whenever you're in contact with dirty surfaces, which is pretty much all the time. And when you pick up your iPhone and bring it to your ear, these germs get transferred to your face where they enter your immune system through the moist mucous membranes of your eyes, mouth and nose.
Specialty glass maker and primary iPhone cover glass supplier Corning thought of that, too, and at the Consumer Electronics Show in Las Vegas announced an antimicrobial version of its Gorilla Glass which uses ionic silver to prevent growth of bacteria and other pathogen organisms...