The truth about the three-seconds rule

At least one study holds clues to how the belief could have come about. In 2003, a study was conducted by Meredith Agle, then a doctoral candidate at the University of Illinois at Urbana-Champaign, and high school senior Jillian Clarke, who was on an internship at the university.

They found few microorganisms after swabbing floors at various locations around the university, including laboratories, halls and dormitories.

Agle suggested this was because the floors were so clean and dry that they prevented the spread of pathogens such as salmonella or listeria, which require moisture to survive.

Conversely, cookies and gummy bears placed on tiles covered with some E. coli saw the bacteria transferred in under five seconds.

For their research, the pair won the 2004 Ig Nobel Prize – a satirical award presented to unusual scientific research that “first makes people laugh, and then makes them think”.

However, Richard Ravel, principal consultant of food safety consultancy Food Forward, said the rule is “largely a myth”.

“Scientific studies have shown that bacteria can transfer to food almost immediately upon contact. The amount transferred depends more on how clean the surface is, the type of food, whether it is wet or dry, and the type of surface than on whether the food was on the surface for one, three or five seconds,” he said.

Moist foods such as watermelon or cooked rice generally pick up bacteria more readily than dry foods like crackers, he noted.

Ravel added that smooth, non-porous surfaces – such as stainless steel, laminate, glass and tiles – allow bacteria to transfer more readily than porous materials such as unfinished wood or carpet, which may trap some bacteria, though he warned that this does not mean such surfaces are “safe”.

While tables in hawker centres and food courts are cleaned regularly, they are not sanitised to the same standard as plates or food preparation surfaces, said Ravel, adding that these tables come in contact with droplets from coughing or sneezing and other contaminants between cleaning.

“The actual risk depends on what microorganisms are present and how many are transferred to the food. Sometimes nothing may happen, but the consequences can range from mild diarrhoea and vomiting to more severe illness requiring medical attention,” he said.

Ravel added that Singapore’s warm and humid climate creates favourable conditions for bacteria to grow if food or surfaces remain dirty.

“This makes cleaning, proper hand hygiene, temperature control and avoiding unnecessary contamination even more important,” he said.

In comments to the original TikTok video, viewers noted that the diner seemed to actually be eating off the lid of a takeaway plastic container. 

“A food-grade plastic lid can work as a plate if it is clean. The concern would only arise if the outside of the lid had been contaminated during transport or storage,” Ravel said.

“In other words, using a clean container lid is not ideal, but it is generally a much better option than eating directly from a public tabletop.”