In a study published in Nature, new data have highlighted the bacterial strain-level sharing rates of mother–offspring pairs, twins, families, cohabiting individuals and individuals within a population, as well as those between different populations, providing a comprehensive view of the transmission landscape of the intestinal and oral microbiome in humans. These findings highlight the need to reassess diseases currently considered to be non-communicable and underscore the importance of considering social structure and transmissibility in the design of microbial studies.