Taking a bite of chips or a vegetable and dipping it again in a common bowl of sauce does transfer bacteria. This is shown by a study by “Clemson“ University, published in 2009 in the Journal of Food Safety. It tested salsa, chocolate sauce and cheese dip, and the highest bacterial contamination was reported for salsa.
In laboratory experiments, three to six dips of already bitten food transferred about 10,000 bacteria from the mouth to the sauce. In real gatherings with more people, researchers have calculated that one bite can transfer between 50 and 100 bacteria from one person to another. The amount depends on the size of the container and the thickness of the sauce.
Salsa is the most easily contaminated
The difference between the three products is related to their consistency and acidity. Thinner salsa is more easily returned to the common container from the bitten piece, and thus more microorganisms get into it. After standing at room temperature, the amount of bacteria in the salsa decreases, probably due to its higher acidity.
Professor of vaccine immunology at Imperial College London John Tregoning warns that the mere transfer of bacteria does not necessarily mean illness. "Bacteria from your mouth probably won't make you sick, but fecal bacteria can," he says, citing salmonella and norovirus as more serious concerns.
The bigger risk comes from your hands
According to doctors, when eating together, what may be more dangerous than bacteria in the mouth are microorganisms transferred from your hands. A person can touch their face, wipe their nose or sneeze, and then take food from a shared plate. This can transfer salmonella, norovirus, rotavirus, dysentery and typhoid fever to the products.
“If I had to choose which is more dangerous – "dipping food twice in the common sauce or not washing your hands and eating with dirty hands, dirty hands are a much more serious risk," commented therapist Nadezhda Chernyshova, quoted by RBC. She specifies that in healthy people, the exchange of common bacteria from the mouth most often does not lead to illness.
People with a weakened immune system and those who have recently taken antibiotics should be more careful, although the risk is not considered high for them either. The simplest measure remains good hand hygiene before eating. When gatherings with more people, experts recommend distributing the sauce in separate dishes or using serving utensils.
Sources: RBC, The Guardian