Nine Gram-positive bacterial species found in cattle intestines were linked to lower childhood asthma and allergy risk in a German study of 1,018 children.
The researchers found the bacteria release airborne compounds that, when inhaled, activate two respiratory receptors that suppress the excessive immune response tied to allergic disease.
Those microbes explained about two-thirds of the protective effect against asthma and roughly half of the protection against hay fever and eczema, while fungi and other microorganisms showed no similar benefit.
The findings suggest therapies could be developed to mimic farm-environment exposure for urban children, adding to evidence that early-life microbial contact helps shape immune development.