Scientists Identify Nine Bacterial Species That May Protect Children From Asthma and Allergies

A group of bacteria commonly found on traditional livestock farms may play a key role in protecting children from asthma, hay fever and eczema, according to new research. The findings provide some of the strongest evidence yet supporting the long-standing hygiene hypothesis, which suggests that early exposure to certain microbes helps the developing immune system learn to respond appropriately instead of overreacting to harmless substances.

The study, published by researchers from LMU University Hospital and Helmholtz Munich, identified nine bacterial species that appear to account for much of the well-known "farm effect"—the observation that children raised on livestock farms develop allergic diseases far less often than children growing up in urban environments.

Scientists searched for the microbes behind the farm effect

For decades, researchers have observed that children living on traditional farms have substantially lower rates of asthma and allergic diseases. Although scientists suspected that microbes were responsible, identifying the specific organisms involved proved difficult.

To investigate, epidemiologist Markus Ege and colleagues analyzed mattress dust collected from 1,018 schoolchildren living in rural southern Germany. The researchers also collected air samples from cow sheds belonging to the farms of 47 participating children, allowing them to compare bacteria found directly in livestock environments with those present inside children's homes.

Using genetic sequencing and advanced bioinformatics, the team compared bacterial communities with children's diagnoses of asthma, hay fever and atopic eczema.

Nine bacterial species stood out

The researchers identified nine gram-positive bacterial species that appeared to explain a large proportion of the farm effect. Among the most important were Romboutsia timonensis and Glutamicibacter arilaitensis.

According to the researchers, these nine species explained approximately two-thirds of the reduced asthma risk observed among farm children. They also accounted for about half of the lower risk of hay fever and atopic eczema.

While the bacteria represented only around 6 percent of all microbes detected in household mattress dust, they made up roughly one-quarter of the bacteria found in cow shed air, suggesting that livestock environments are their primary source.

The bacteria may train the immune system

The study suggests these microbes originate mainly in the digestive systems of cattle before entering the surrounding environment through manure. Children living on farms are repeatedly exposed while spending time around livestock and later carry the bacteria into their homes, where they remain present in household dust.

Scientists believe this continuous low-level exposure helps educate the immune system during childhood.

Laboratory analyses showed that metabolites produced by these bacteria activate a receptor called the aryl hydrocarbon receptor (AhR), which helps regulate immune function and gene activity. Moderate activation of this receptor appears to stimulate anti-inflammatory pathways that reduce the likelihood of allergic responses.

The researchers also note that excessive activation may not be beneficial, indicating that both the amount and timing of exposure are likely to be important.

Stronger support for the hygiene hypothesis

The findings provide important biological evidence for the hygiene hypothesis, which proposes that reduced microbial exposure early in life contributes to rising allergy rates in industrialized societies.

Rather than relying solely on broad associations, the study identifies specific bacterial species, the compounds they produce and the immune receptor they appear to influence.

However, the researchers emphasize that the study remains observational. Although the associations are strong, it cannot prove that these bacteria alone directly prevent allergic diseases. Other environmental exposures, genetics and lifestyle factors almost certainly contribute as well.

Potential for future allergy prevention

The researchers caution against trying to deliberately expose children to farm dust, as farm environments can also contain harmful pathogens and pollutants.

Instead, they hope these discoveries will help scientists develop safe microbial-based therapies or preventive treatments that reproduce the beneficial effects of farm exposure without the associated risks.

Asthma and allergic diseases remain among the most common chronic health conditions affecting children worldwide. By identifying specific bacteria that appear to protect against these illnesses, the study provides researchers with new targets for developing future prevention strategies.

The team plans to continue investigating exactly how these bacterial species communicate with immune cells and regulate inflammation. Better understanding these molecular interactions could eventually lead to new approaches for preventing allergies during early childhood while safely supporting healthy immune development.