The study investigates the microbial communities of 159 individuals and 36 dogs from 60 families, focusing on the impact of cohabitation and dog ownership on microbial exchange. Key findings include: 1. **Family Members Share Microbiota**: Co-habiting family members, particularly couples, share more of their microbiota than individuals from different households. The strongest effect is observed on skin, followed by oral and fecal microbiota. 2. **Dog Ownership Increases Skin Microbiota Sharing**: Dog ownership significantly increases the shared skin microbiota among cohabiting adults, with dog-owning adults sharing more 'skin' microbiota with their own dogs than with other dogs. 3. **Age-Related Changes in Microbiota**: The study also examines the impact of age on the human microbiota, finding that the gut microbiota undergoes significant changes over the first three years of life, while the skin and tongue microbiota show relatively stable diversity and composition. 4. **Environmental and Contact Factors**: The results suggest that direct and frequent contact with cohabitants, including pets, significantly shapes the composition of microbial communities, particularly on the skin. 5. **Mechanistic Considerations**: The presence of dog-derived bacterial taxa on the skin of dog owners may contribute to the observed similarity in microbiota between dog owners and their dogs. 6. **Implications for Health and Disease**: Understanding the impact of environmental factors on microbial communities may help in preventing or treating diseases, particularly in the context of the hygiene hypothesis and immune regulation. Overall, the study highlights the importance of considering the role of cohabitation and pets in shaping the human microbiome, emphasizing the need for further research to understand the functional implications of these microbial exchanges.The study investigates the microbial communities of 159 individuals and 36 dogs from 60 families, focusing on the impact of cohabitation and dog ownership on microbial exchange. Key findings include: 1. **Family Members Share Microbiota**: Co-habiting family members, particularly couples, share more of their microbiota than individuals from different households. The strongest effect is observed on skin, followed by oral and fecal microbiota. 2. **Dog Ownership Increases Skin Microbiota Sharing**: Dog ownership significantly increases the shared skin microbiota among cohabiting adults, with dog-owning adults sharing more 'skin' microbiota with their own dogs than with other dogs. 3. **Age-Related Changes in Microbiota**: The study also examines the impact of age on the human microbiota, finding that the gut microbiota undergoes significant changes over the first three years of life, while the skin and tongue microbiota show relatively stable diversity and composition. 4. **Environmental and Contact Factors**: The results suggest that direct and frequent contact with cohabitants, including pets, significantly shapes the composition of microbial communities, particularly on the skin. 5. **Mechanistic Considerations**: The presence of dog-derived bacterial taxa on the skin of dog owners may contribute to the observed similarity in microbiota between dog owners and their dogs. 6. **Implications for Health and Disease**: Understanding the impact of environmental factors on microbial communities may help in preventing or treating diseases, particularly in the context of the hygiene hypothesis and immune regulation. Overall, the study highlights the importance of considering the role of cohabitation and pets in shaping the human microbiome, emphasizing the need for further research to understand the functional implications of these microbial exchanges.