Couples who live together share many things, including bacteria. A study of the skin’s microbial composition conducted by the University of Waterloo, Canada, found that each individual in a couple who lives together has a significant impact on the microbial communities of their partners.
A publication in the journal from the American Society for Microbiology states that commonalities were sufficiently strong for computer algorithms to identify cohabiting partners with 86% accuracy, based exclusively on skin microorganisms. https://www.asm.org/index.php/newsroom/item/6698-not-under-the-skin-but-on-it-living-together-brings-couples-microbiomes-together