How safe is it?

Momlogic's Vivian: My kids have done it. Your kids have done it. A chocolate chip cookie or some other irresistible morsel of tasty goodness slips out of their grasp and onto the ground, and the lure of snatching it up again and shoving it in one's mouth like it never happened sure is powerful.

But should we let our kids do this? After all, how many germs can jump on a single cookie in three seconds?

Dr. Philip M. Tierno, author of The Secret Life of Germs: Observations and Lessons from a Microbe Hunter, and director of Clinical Microbiology and Immunology at the New York University Langone Medical Center, hereby explains why there is no such thing as a "three-second rule."

"The whole world is bathed in germs, whether it's people, their byproducts like feces or sputum, or the earth. Germs were here before people, and they'll be here after people," says Dr. Tierno. "Having said that, if someone were to vomit in front of you, or if you should see dog feces on the ground, or if you should see someone urinating or expectorating on the ground and your food drops anywhere near that, would you eat it? Of course not! The same concept applies when you drop food on the ground. When you walk where all those things have been outside, you bring them onto your carpeting and onto your floors. You may have stepped on a spot where someone once vomited, and your shoes can pick up portions of the Norovirus, also known as the diarrhea/vomit virus. If you drop food on that, it picks it up. Even if you remove your shoes, your feet hold a repository of germs that can be transmitted onto foodstuffs."

Even in three seconds?

"It's impossible to quantify how many germs could adhere to a cookie in three seconds. It's one of the vagaries of life. But in three seconds, that cookie could contain the Norovirus or other pathogens that can make you really, really sick," says Dr. Tierno.

Yikes! Even if you just washed the floor?

Dr. Tierno says there's no reprieve in this scenario, unless you are sterilizing your floor. Which you aren't. "Even if you wipe your floor with Clorox, it's exposed to air, and by definition isn't sterile," he adds.

So the next time your kid drops food on the floor, by all means, throw it away and replace it if you can. But even with all these germs infesting your existence, Dr. Tierno says there's no need to become a germaphobe -- just be cautious and teach your kids how to wash their hands.

"You should be aware of germs and how to interfere or break their transmission of those pathogenic types. Of 60,000 types of germs, only 1-2% are pathogenic," he says.

Vivian Manning-Schaffel is Momlogic's East Coast Editor. She's also written for Babble, Parenting, The Advocate, The New York Post, Business Week and a variety of other publications and lives and works in the heart of breeder Brooklyn with her husband and two kids. She authors two pop culture blogs: The Mad Mom and A Hag Supreme, and is on the web at vivianmanningschaffel.com.