Shared Living: How People Who Live Together Share About 25% of Their Microbiome

People who live together share roughly a quarter of their gut microbiomes, according to a study published June 15, 2026 in Nature Microbiology, marking the first large-scale analysis of how shared environments reshape microbial communities over time.

The research, led by microbiologists at the University of Amsterdam and the Netherlands Cancer Institute, analyzed stool samples from 1,200 Dutch households over 18 months. Couples and roommates showed an average 23% overlap in their gut bacteria, with the effect strongest in those living under one roof for more than five years. "We expected some sharing, but the scale surprised us," said study co-author Dr. Ellen Zoetendal, a microbiome researcher at the Netherlands Cancer Institute. "Even after accounting for diet and genetics, proximity was a dominant factor."

The findings challenge assumptions that gut microbiomes are primarily shaped by individual diet and genetics. While diet accounted for 12% of microbiome similarity and genetics for 8%, shared living space explained nearly double that. The study also noted that pets in the home further increased microbial overlap, suggesting animals act as additional vectors for microbial exchange.

Researchers caution the results do not imply shared microbiomes are inherently beneficial or harmful. "This is observational data," Zoetendal emphasized. "We can’t say whether sharing microbes is good or bad for health—just that it happens." Previous smaller studies had hinted at microbiome convergence in couples, but this work provides the most robust evidence to date, with sample sizes 10 times larger than prior research.

The study aligns with emerging research on "microbiome contagion," where shared environments—from households to daycare centers—appear to drive microbial similarity. A 2024 study in Cell found that infants in the same nursery shared up to 30% of their gut bacteria, while a 2025 Science paper linked household microbial diversity to reduced allergy risks in children. The Dutch findings add weight to the idea that public health strategies might need to account for microbial exposure beyond individual behaviors.

What remains unclear is whether the shared microbes confer any measurable health benefits. Some bacteria, like Bacteroides and Prevotella strains, are linked to digestion and immunity, but others may carry risks if transferred between immunocompromised individuals. The research team is now investigating whether microbiome similarity correlates with shared health outcomes, such as metabolic disorders or immune responses.

For now, the study underscores how deeply our microbial communities reflect our social lives—a reminder that even our invisible ecosystems are shaped by the people and pets we share our homes with.

Why does shared living increase microbiome overlap?
The study identified three primary mechanisms: direct transfer via surfaces (e.g., food preparation, shared utensils), airborne microbial particles, and indirect routes like pets. Air sampling in test households revealed that up to 15% of airborne microbes originated from human skin or gut bacteria, with higher concentrations in shared kitchens and bathrooms.

Could shared microbiomes affect disease risk?
Early evidence suggests potential links to autoimmune conditions and obesity, but the Dutch study did not examine health outcomes. A 2023 JAMA Network Open analysis found that couples with similar gut bacteria had a 20% lower risk of type 2 diabetes, though the authors cautioned against overinterpreting the correlation. "We need longitudinal studies to separate cause from effect," said Dr. Zoetendal.

How does this compare to prior research?
While earlier studies (e.g., a 2019 mBio paper on couples) reported microbiome convergence, they lacked the scale or duration of the Dutch study. The new work also controlled for more variables, including medication use and household cleaning routines. A side-by-side comparison of key findings:

What’s next for microbiome research?
The Dutch team is launching a follow-up study to track whether microbiome similarity predicts shared health trends, such as metabolic changes or immune responses. Meanwhile, researchers at Harvard are exploring whether targeted microbial transfers could treat conditions like irritable bowel syndrome. "This opens doors to understanding how we might engineer microbial communities for health," said Dr. Curtis Huttenhower, a microbiome expert at Harvard T.H. Chan School of Public Health.

For the public, the findings may prompt questions about hygiene practices. While shared microbes are normal, individuals with weakened immune systems may wish to discuss precautions with healthcare providers. The study authors stress that handwashing and surface cleaning remain critical—even as they acknowledge our microbiomes are inherently social.