Old Friends hypothesis
The Old Friends hypothesis is the hypothesis that the human commensal microbiome has been substantially altered or reduced in humans living modern lifestyles.[1] These changes, according to the hypothesis, have led to rapid increases in certain immunological and other diseases.
Overview
The old friends hypothesis was first proposed in 2003.[2] It is a modified version of the hygiene hypothesis, which suggests a link between early microbial exposure and immune system development. This is commonly believed to be related to environmental bacteria, improvements in hygiene and sanitation, or childhood infections. However, researchers such as Martin Blaser have proposed that most of the observed changes are mediated by commensal bacteria rather than pathogens or soil microbes.[3] Additionally, it suggests that these commensals could influence other body systems.[4]
Evidence
The incidence of allergies, autoimmune diseases, and nonspecific inflammation has been increasing in developed nations for decades.[1] Multiple potential reasons were proposed for this phenomenon. In the late 20th century, it was discovered that children with multiple older siblings and those living on farms had lower allergy rates than other children.[5][6]
See also
References
- ^ a b Rook, Graham A. W. (2023). "The old friends hypothesis: evolution, immunoregulation and essential microbial inputs". Frontiers in Allergy. 4 1220481. doi:10.3389/falgy.2023.1220481. ISSN 2673-6101. PMC 10524266. PMID 37772259.
- ^ Rook, Graham A.W.; Martinelli, Roberta; Brunet, Laura Rosa (October 2003). "Innate immune responses to mycobacteria and the downregulation of atopic responses:". Current Opinion in Allergy and Clinical Immunology. 3 (5): 337–342. doi:10.1097/00130832-200310000-00003. ISSN 1528-4050.
- ^ Blaser, Martin J.; Falkow, Stanley (December 2012). "What are the consequences of the disappearing human microbiota?". Nature Reviews Microbiology. 7 (12): 887–894. doi:10.1038/nrmicro2245. ISSN 1740-1534. PMC 9354563.
- ^ "Disappearance of the Human Microbiota: How We May Be Losing Our Oldest Allies | ASM.org". ASM.org. Archived from the original on 2025-11-20. Retrieved 2026-01-26.
- ^ Strachan, D. P. (1989-11-18). "Hay fever, hygiene, and household size". BMJ. 299 (6710): 1259–1260. doi:10.1136/bmj.299.6710.1259. ISSN 0959-8138. PMC 1838109.
- ^ von Mutius, Erika; Vercelli, Donata (December 2010). "Farm living: effects on childhood asthma and allergy". Nature Reviews. Immunology. 10 (12): 861–868. doi:10.1038/nri2871. ISSN 1474-1741. PMID 21060319.