Think about how many people have touched the tables, napkin dispensers and chair backs at a mall food court or restaurant, and you have another reason to wash your own hands or use a hand sanitizer. Just as kitchen sponges offer a warm, moist environment that lets food bacteria to multiply, the rags used to wipe down dirty tabletops are "a decent medium for bacteria to dwell in," Boscamp said.
Most people grip the handrails when riding escalators inside malls and stores, leaving behind normal skin bacteria plus other germs picked up from rubbing their noses or mouths. Schaffner said he's not too worried about this particular hazard.
"If you use your hand sanitizer periodically during your afternoon safari at the mall, I think you'll be pretty well-protected," he said.
Boscamp thinks of escalator handrails the way he thinks about the metal bars subway riders hang onto.
"It's probably a good idea after contact with things like that to be thinking about Purell," he said.
All those sniffling tots inside toy stores, along with the healthy ones who just like to put everything in their mouths, can leave invisible coatings of germs behind -- not to mention what they spew into the air when they sneeze or cough.
"The number of hygienic children in the United States I can count on the fingers of my hands," Schaffner said. "I have to admit, children are the great disseminators of respiratory viruses. They do so because, first of all, when a virus infects a child, the child actually breathes out a lot of virus, more so than adults. They do so for a longer period of time."
Although most toys remain in the boxes and packages in stores, any that are unwrapped and available for children to touch, lick or rub against their runny noses could become infection-spreaders, Boscamp said. That's why his medical center and others request that any holiday donations of toys for sick hospital patients be in original, sealed packaging.
"We don't take chances," he said.
The slick surfaces of smart phones and tablet computers can harbor a variety of germs, including staph, capable of living several hours. However, just because environmental hygienists can swab such surfaces and find a variety of bacteria doesn't mean they necessarily will make you sick, said Schaffner.
"Try out your candidate iPhone, look at it, play with it, and then do your hand sanitizer thing," he said.
Some Surfaces Not to Worry About
Although women frequently hear they should avoid shared testers at makeup counters, "infections associated with shared makeup are virtually nonexistent," Schaffner said. "They are not a recognized public health problem."
Worries about picking up germs from ATMs at the mall might be exaggerated, too, even if you've never see a bank employee wiping down ATM keys.
"If for some reason, you're a little queasy [about uncleaned keys], go to the ATM, get your cash and use your hand sanitizer," Schaffner said.
Schaffner made his comments just before heading off to the gym, where he relies on hand washing and hand sanitizer.
"I don't rub down machines," he said. "By protecting ourselves with our hand sanitizers, I don't think we have to go around sani-wiping the world."
A version of this story previously appeared on ABCNews.com.