Almost everyone – at least in the United States – does it. A cookie, candy, or orange rolls onto the floor, and common wisdom dictates that it’s safe to eat as long as it was there no longer than five seconds. You can even blow it off to be safe.

But Jorge Parada, MD, MPH, FACP, FIDSA, medical director of the infection prevention and control program at Loyola University Health System, says that common folklore is false. Any object that falls onto the floor is immediately contaminated. He says in fact that the five-second rule should be replaced with a new aphorism: ‘When it doubt, throw it out.’

Any item that makes contact with a surface will then come into contact with bacteria – and dirt. The number of bacteria and the type of microbe is dependent on the object dropped and the surface with which it makes contact.

For example, Parada says, if you drop a hot dog on the floor, you might do well to wash it off. But even rinsing the hot dog may not remove all of the bacteria. And, he continues, if you drop an item, and 1,000 bacteria migrate to it, maybe you will be fine, since the average person requires 10,000 bacteria in order to become infected. But maybe your threshold – or that of a loved one – is lower.

There are degrees to contamination though, Parada says. A potato chip scooped up after two seconds from its descent onto a clean table will probably not be wildly contaminated with bacteria. On the other hand, that same potato chip on a more severely contaminated surface, like the floor, after a minute? Parada says that it would be better just to throw that one out.

And some food items will fare better than others – like a piece of rock candy, as opposed to a piece of Swiss cheese.

He also adds that no one is helped when parents use their own mouths to clean off a pacifier.

While humans do build up a certain degree of immune resistance against common exposure, Parada says that is not a reason to put oneself in harm’s way. The best way, he says, to help your immune system is simply a balanced diet, a good amount of rest, exercise – and being up to date on vaccines.

Parada admits to sometimes using the five-second rule on occasion.