This practice does transmit mouth bacteria, but don’t panic
Double-dipping means eating part of a piece of food and then putting it back into a communal dip – for example, biting a carrot and dipping it into shared hummus, or redipping a half-eaten tortilla chip in salsa. The concern is that bacteria from your mouth get transferred into the dip and could cause illness in the people you’re sharing it with.
“You do transmit bacteria from the food you have eaten back into the source,” says Prof John Tregoning, the author of Live Forever? A Curious Scientist’s Guide to Wellness, Ageing and Death. He points to a study testing salsa, chocolate sauce and cheese dip, which found bacteria were transferred to all three, with salsa showing the most contamination.