You share a third of your oral bacteria with other people in your home

Many bacteria form spores that can survive in the air, leading to intra-household transmission of micro-organisms, even if household members are not in close relationships with each other.

You can share more than you think with the people you live with, including up to a third of the strains of bacteria in your mouth.

Physicians are increasingly interested in the health effects of the many hundreds of species of bacteria, viruses, fungi, and parasites that live in our gut, mouth, and other parts of our body and on it, known as the microbiome.

Nicola Segata of the University of Trento in Italy and colleagues analyzed the results of 31 previous microbiome studies of people living together or near each other in 20 countries, including parts of Europe, North and South America, Africa and Asia.

The studies included about 10,000 fecal or saliva samples and recorded whether household members were partners, relatives or friends. The bacterial strains present have been genetically identified.

The team found that household members were more likely to share common strains of bacteria in their mouths than in their guts.

In all studies, 32% of oral bacterial strains were shared by household members compared to 12% of intestinal bacterial strains. Only 3 percent of oral bacteria were the same among non-cohabiting members of the same population.

This shows how often people pass the bacteria on to others, even those they don’t kiss or have sex with, says Segata.

Oral bacteria can be easily separated, he says, because many bacteria form spores that can survive in the air for a long time.

Joanne Santini of University College London says that people living together can eat the same food, which could help create a comparable mouth environment that encourages the same strains of bacteria to multiply.