To begin, the influenza virus mostly spreads via tiny droplets in the air (for example, from sneezes)—not by dirty hands or surfaces—which limits the role of Purell. It probably wouldn't matter even if flu transferred though hand contact, which is how most cold viruses spread...The average child touches his or her mouth and nose every three minutes, and both adults and children come in contact with as many as 30 different objects every minute. Even hospitals can't get staff to use Purell before seeing patients; it's impossible for day care staff, parents, or teachers to wash a child's hands 20 times each hour.But what about adults? For that, I immediately thought of the Peltzman Effect.
Sam Peltzman discovered that increased safety standards on cars don't reduce accident fatalities. Because cars are safer, people feel safer and drive more recklessly. Similarly, hand sanitizer makes people feel braver and expose themselves to more germs. On net, there's no change, but it's not Purell's fault.