Bacteria identified as key to protecting children from allergies

An international research team has identified nine specific bacteria that may protect children from asthma, allergic rhinitis, and atopic dermatitis. The study, which analyzed over one thousand European participants, provides a biological explanation for the ‘farm effect’—the phenomenon where children raised in rural environments exhibit lower rates of allergies compared to those in urban centers.

Researchers led by epidemiologist Markus Ege from LMU University Hospital in Munich found that these bacteria produce metabolic substances present in stable air and dust. When inhaled, these substances activate receptors in the respiratory tract, reducing inflammatory responses. These specific microbes are estimated to account for approximately two-thirds of the protective effect against asthma.

This discovery refines the long-standing ‘hygiene hypothesis.’ While the original theory suggested that a general lack of microbial contact weakens immunity, experts like Chilean allergist Arturo Borzutzky note that the old theory failed to explain why many urban residents in Latin America still develop asthma despite bacterial exposure. The new findings suggest that specific microbial signals, rather than just general exposure, are the key drivers of immune training. Researchers noted that this effect is most potent during the first years of life, though they cautioned that air pollution and smoking remain significant risk factors for asthma.