UNMC News

Dropped it; should you eat it? The five-second rule revisited

An answer to the age-old question.

By Michael Huckabee, Ph.D., professor and director of the University of Nebraska Medical Center physician assistant program.

So that last bite of a tasty morsel just dropped to the floor. The five-second rule says if we’re quick about it, we can still pop it in the mouth and enjoy it. A few years ago, research disagreed. In a 2007 study, crops of Salmonella, the bacteria that causes fits of diarrhea, were placed on wood, tile and carpet. Pieces of bologna were then dropped on the surfaces for 5, 30 and 60 seconds. On the wood and tile surfaces, 99 percent of the bacteria were transferred nearly immediately. Same results occurred with the carpet, though a smaller amount of bacteria were transferred. With a warning that as few as 10 salmonella bacteria can cause gastroenteritis, doctors warned that the five-second rule should be trashed.

But sometimes research just doesn’t add up. Kids throw all kinds of things in their mouths, and rarely do we see it result in illness. In fact, developed countries carry a reputation for being too clean. Associated with this cleanliness are the increased incidence of hay fever, eczema, and more serious diseases such as asthma, inflammatory bowel disease, multiple sclerosis and type I diabetes. So should playing in the dirt be banned, or do we welcome it?

The hygiene hypothesis offers a possible answer. It suggests that if we stay too sanitized, we can’t ward off some diseases. Here’s the reasoning. Our immune system kicks in without our knowing it whenever we ingest, inhale or touch a substance that represents foreign material to our bodies. That’s called an antigen. The body fires up in response to these antigens, making a variety of cells and antibodies. Sometimes it triggers an allergic response (we sneeze, itch, or develop a rash), and sometimes we become desensitized to the antigen and it doesn’t ever bother us again. We just don’t know what triggers what.

Lots of things can be innocuous antigens, but often its bacteria and viruses. Being around dirt exposes us to more antigens. If we tolerate it as kids, we build up a response to those dirty antigens and we’re all the healthier for it. That’s the yet unproven hygiene hypothesis.

We may be closer to how it all works. A recent research study looked at what parents do to clean off a dropped infant pacifier. Turns out moms who gave it a quick wash in their own mouths left a bundle of new bacteria on the sucker. When it went back into little Billy, it exposed him to a new crowd of organisms. Gross, maybe. But those same kids enjoying the licked-clean pacifiers were less likely to get eczema and asthma later as kids.

So maybe we can combine the five-second rule with the hygiene hypothesis and add a dose of common sense. Do all we can to avoid Salmonella, check. Playing in the dirt? The more the merrier. And licking the pacifier? Let’s leave that up to mom.

Contact

Vicky Cerino
UNMC Public Relations
(402) 559-5190
vcerino@unmc.edu