Scientists Identify Nine Bacteria Behind Farm Children's Lower Allergy Risk

Children who grow up on farms develop asthma, hay fever, and eczema far less often than other children — a phenomenon researchers have long called the farm effect. An international team led by epidemiologist Markus Ege at LMU University Hospital Munich has for the first time pinpointed the specific bacteria responsible for much of this protection.

Nine Bacteria Explain Most of the Protective Effect

The research team analyzed data from more than 1,000 children across European studies, examining nasal swabs and dust samples from apartments and cattle barns. Using modern genetic and metabolic analysis techniques, they identified nine bacteria closely associated with protection against asthma and allergic diseases. These nine bacteria account for approximately two-thirds of the protective effect against asthma and around half of the protective effect against hay fever and eczema in farm children.

Specific Microbes, Not General Exposure, Are Key

The findings refine the long-standing hygiene hypothesis of 1989, which proposed that immune systems develop poorly when children encounter too few microbes early in life. The new study suggests it is specific microbial signals — not simply greater microbial diversity — that confer protection. Chilean allergologist Arturo Borzutzky noted that the simpler form of the hypothesis cannot explain why many urban Latin Americans, also exposed to many bacteria, still develop asthma. The research opens a path toward future interventions that could one day extend the farm protective effect to children not growing up on farms.