Is it true that … you have five seconds’ grace after dropping food on the floor?

You drop a piece of cucumber on the floor. Do you immediately throw it in the bin or rely on the age-old “five-second rule”? John Tregoning, professor of vaccine immunology at Imperial College London, has some bad news: he refers to three studies into bacteria transfer that all point towards the rule being false.

In the first study, scientists dropped a range of foods — bread, buttered bread, watermelon and gummy bears — on surfaces (tile, steel, wood and carpet) that had been coated with bacteria. “They transferred almost immediately,” he says, and the worst combination for transfer was when wet food hit a solid surface, such as watermelon on tile or steel.

Another study, in which cooked sausage was dropped on to surfaces, showed bacteria transferred on to the meat even if they had been applied to the surface hours earlier. “If you put a piece of contaminated chicken on to a work surface and then, two hours later, drop your piece of bread on to it, you can still pick up bacteria from it.

United Kingdom, London

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