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

You may share more than you realise with the people you live with – including up to a third of the strains of bacteria in your mouth.

Doctors are increasingly interested in the health impacts of the many hundreds of species of bacteria, viruses, fungi and parasites that live in our gut, mouth and elsewhere in and on our bodies, known as the microbiome.

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

The studies included nearly 10,000 samples of either faeces or saliva and had recorded if the household members were partners, relatives or friends. The bacterial strains present were identified genetically.

The team found that household members were more likely to share mouth bacterial strains than those of the gut.

Across all the studies, 32 per cent of strains of oral bacteria were shared by household members, compared with 12 per cent of gut bacteria strains. Only 3 per cent of mouth bacteria were the same among non-cohabiting members of the same population.

This shows how common it is for people to transmit bacteria to others, even those they don’t kiss or have sex with, says Segata.

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

Joanne Santini at University College London says people living together may be eating similar food, which could contribute to a comparable environment in the mouth that would encourage the same strains of bacteria to thrive.