Food can still look appetizing after it has fallen on the floor. But is it safe to eat?

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If you're like most people, you eat it. Maybe you follow the "5-second rule," which claims foods are safe to eat if you pick them up within 5 seconds of dropping them.

But you might want to think again. Scientists now say that 5 seconds are all it takes for foods to become contaminated with enough bacteria to make you sick.

Bacteria are single-celled organisms that can cause many kinds of illnesses. Some kinds of bacteria can grow on food. If we eat foods on which these bacteria are growing, we can become sick. Common symptoms include vomiting and diarrhea.

One of these food-borne bacteria is Salmonella. It makes 1.4 million people sick every year. Earlier this year, 370 people became sick after eating peanut butter that had been contaminated with Salmonella at the manufacturing plant. Salmonella are often found in raw eggs and chicken. Cooking kills these bacteria, which is why it is so important to cook eggs, chicken, and other foods thoroughly.

Being a good housekeeper is a second tip for preventing infection. If household surfaces aren't washed thoroughly, they can support Salmonella for weeks.

But how long does it take these bacteria to attach to food? To answer that question, a team of scientists at Clemson University in South Carolina decided to test the 5-second rule, using sandwich ingredients. First, they placed a known amount of Salmonella cells on three surfaces: wood, tile, and carpet. They placed a slice of bread and a slice of bologna on each surface for 5, 30, or 60 seconds.

After just 5 seconds, both the bread and bologna picked up enough bacteria to make you sick.

"Someone making a sandwich might follow someone who, a day before, used that surface to cut meat or another raw food. It might not look contaminated, but could have bacteria that would be harmful," said Paul Dawson, the food scientist who led the study.

So, forget the 5-second rule. If your toast lands on the floor, toss it out. Stick a fresh slice of bread in the toaster. And this time, be careful not to drop it!—Jennifer Cutraro