Eating dropped food can cause food poisoning even if it’s picked up immediately.
You’ve just made a cup of tea when you drop the last chocolate digestive from the packet.
You quickly scoop it up and pop it in your mouth, secure in the knowledge it only briefly touched the floor.
But now scientists have warned the unwritten ‘five second rule’ could end up causing food poisoning or worse.
Oops: Wet food will pick up more bacteria than dry food, but all dropped snacks will pick up some bugs.
The well-known rule states it is safe to eat food dropped on the floor as long as it is picked up within seconds.
But the stray biscuit, chip or piece of toast is likely to collect a ‘new cargo of bugs, however quickly you pick it up,’ according to New Scientist.
The question featured in the magazine’s ‘Last Word’ section where readers pose open questions for the scientific community to answer.
It said: ‘If you drop a piece of food on the floor, it is supposedly safe to eat it as long as you pick it up before 10 seconds has elapsed, because it takes that amount of time before it can be colonised by microbial life. Is there any truth in this whatsoever?’
The theory is commonly used in the UK, America and elsewhere. In Russia, for instance, there is a saying: ‘Promptly picked up is not considered fallen.’
But a succession of subscribers said the theory was untrue, partly because so many factors are involved such as cleanliness of the floor and type of food.
One stated, simply: ‘When you drop food, two things are likely to happen; traces of the food stick to the floor, and trace of the floor (or what’s on the floor) stick to the food.
‘So unless the floor is surgically clean, the food will have acquired a new cargo of bugs, however quickly you pick it up.’
Another reader described the rule as ‘a polite fiction, – everyone known it is an urban myth but plays along.’
Those who preach the homespun philosophy are most likely simply trying to justify not wasting food.
The best way to disprove the theory is to sprinkle castor sugar thinly on to the floor, drop a sweet on to it and catch the sweet as it bounces.
It will have tiny traces of the sugar on it – but if it was bacteria it would be enough to infect ‘a ward full of patients’ said the journal.
It added: ‘Cholera needs perhaps half a million cells to establish an infection – this is a barely visible speck.’