Children who grow up on farms are less likely to develop asthma and allergies. But why? An international research team has now uncovered an important part of the so-called farm effect. The findings point to specific bacteria in livestock housing, their metabolites, and two receptors in human airway cells. For many years, researchers have observed that children growing up in farming environments are less likely to develop asthma, hay fever, and atopic dermatitis. One possible explanation is their frequent exposure to a diverse microbial environment, particularly in cattle barns. However, it has remained unclear which microorganisms may actually provide this protective effect. An international research team led by Prof. Dr. Markus Ege, DZL researcher at the CPC-M site, has now investigated this question. Their findings have been published in NEJM Evidence.
For the study, the researchers analyzed samples and health data from more than 1,000 children participating in European studies. Among other things, they examined nasal swabs and dust samples from the children’s environments. Dust samples from cattle barns were also included. Using advanced genetic and metabolomic analyses, the researchers identified specific bacteria that were particularly strongly associated with protection against asthma and allergic diseases. These included, for example, Romboutsia timonensis and Glutamicibacter arilaitensis. The findings were subsequently validated using data from France and Finland. According to the team’s analyses, the identified Gram-positive bacteria account for a substantial proportion of the farm effect: around two-thirds of the effect on asthma and approximately half of the effect on hay fever and atopic dermatitis.
The bacteria’s metabolites appear to be key. These include kynurenine, xanthine, alpha-linolenic acid, and stearidonic acid. These substances can be inhaled from the air in livestock housing and interact with cells in the respiratory tract. Two receptors, AhR and PPARγ, play an important role in this process. Among other functions, they are involved in regulating the immune system and could help prevent excessive inflammatory responses. The findings provide, for the first time, a clearer picture of an important part of the biological chain underlying the farm effect:
Farm environment → bacteria → metabolites → receptors → immune response
“With our new study, we can identify the individual links in the suspected causal chain,” explains Markus Ege.
The findings provide new starting points for further research into the molecular mechanisms underlying the farm effect. In the long term, they could also inspire approaches to mimic this natural protective mechanism—for example, through agents that target specific microbial metabolic pathways or receptors.
The farm effect could therefore become more than an epidemiological phenomenon. It may also serve as a model for understanding how the microbial environment influences the development of asthma and allergies.
Source: LMU Klinikum
Original publication: Pagani G, Loss G, Pechlivanis S, Depner M, Müller C, Ru J, Strunz-Lehner C, Humphrey G, Ackermann G, Amir A, Melnik A, Garg N, Knight R, Dorrestein PC, Schmitt-Kopplin P, Deng L, Schloter M, Divaret-Chauveau A, Roduit C, Karvonen AM, Genuneit J, von Mutius E, Ege MJ. Gram-Positive Bacteria and the Inverse Association between Farm Exposure and Childhood Asthma. NEJM Evid. 2026 Aug;5(8):EVIDoa2500271. doi: 10.1056/EVIDoa2500271. Epub 2026 Jul 28. PMID: 42517701.
