If you're a double-dipper or a fan of the five-second rule, what you're about to read may prompt a rethink among followers of these frowned-upon habits.

Food scientist Paul Dawson, the author of Did You Just Eat That?, has conducted rigorous tests to see if science supports detractors of the double dip.

He told Alex Hyman on ABC Radio Perth that having a second swipe of communal dip with a half-eaten chip was riskier than he first thought.

Loading...

"We used a cracker and dipped that in chocolate dip, cheese dip and salsa," Professor Dawson said.

"I expected there to be not really much bacteria transfer because of the small surface area on a cracker or chip when you bite it.

"But we actually found there was 1,000 more bacteria per millilitre in the dip from when you bit the chip than when you didn't.

"That's a significant amount ... that's more like a person-to-person transfer like the common cold and other contagious diseases rather than the typical food-borne illness like E.coli and salmonella."

Game of 'Russian roulette'

Professor Dawson also put the five-second theory to the test by introducing harmful bacteria on to tiles, wooden floorboards and carpet.

He dropped food on the surfaces, picked it up after five seconds and then measured the amount of bacteria that had transferred across.

"It's kind of like you're playing Russian roulette," he said.

"It depends on the surface — if there is pathogenic bacteria on that surface, then no, it is not safe to eat.

"But honestly, most surfaces are not going to have any kind of dangerous bacteria there."

Harmful bacteria found on carpets, floorboards and tiles can easily transfer to food. ( ABC Radio Perth: Gian De Poloni )

Fluffy carpet soaks up salmonella

Somewhat surprisingly, carpet actually proved a safer place to drop food than tiles or floorboards.

"The carpet actually soaked up the salmonella we placed on it," Professor Dawson said.

"The carpet fibres stick up and so there wasn't much salmonella to be in contact with the bread and baloney we dropped.

"Most of us have probably used the five-second rule and not gotten sick, but again it depends on the surface.

"If you're in a place where people are preparing raw food, it may not be a good idea."

It is estimated 4.1 million Australians get some form of food poisoning every year. ( Supplied: iStockPhoto )

Food for thought

Using common sense was the most effective safeguard against food poisoning, Professor Dawson said.

"Some common tips that are not really earth-shattering are keep cold things cold, keep warm things warm, don't leave things out overnight.

"Sauces have that possibility that if you leave them out and don't put them in the refrigerator right away, spores can germinate and cause food poisoning.

"A lot of people do get sick every year from eating food and some people actually die from food poisoning.

"There are some cases where you need to be a little more careful — the elderly and people who have an illness and are not quite back at full strength."