Think your roommate’s worst habit is stealing your leftovers?
Science has some bigger news: they’re also sharing your bacteria.
Every meal around the dining table, every chat in the living room, every shared bathroom, and every kiss quietly pass along millions of tiny microbes. While you can’t see them, they’re constantly moving from one person to another.
A new study published in Cell Press Blue found that people living under the same roof share far more bacteria than those living apart. After studying 430 people from 207 households in Italy and Fiji, researchers found that housemates shared about one-fifth of the bacteria in their intestines and one-fourth of the bacteria in their mouths.
Couples topped the list, sharing nearly half of their mouth bacteria—a finding researchers say is most likely explained by kissing.
That may sound alarming, but don’t start eating dinner alone just yet.
Most of these microbes are actually good for us. They help digest food, support our immune system, and even keep harmful germs from taking over. In fact, our bodies are home to trillions of bacteria, and many of them are essential for good health.
The bigger surprise was that some of the bacteria that spread most easily between people have also been linked to diseases such as type 2 diabetes and colorectal cancer. Researchers believe these microbes may simply be tougher survivors, allowing them to move more easily from one person to another.
The study doesn’t suggest that living with family or loved ones is risky. Instead, it shows that our health is influenced not only by what we eat or how we exercise, but also by the people we share our lives with.
So the next time someone borrows your coffee mug, remember—they’ve probably already borrowed a few microbes, too. Fortunately, most of those tiny houseguests are perfectly welcome.
