NEW ORLEANS — The mix of bacteria and fungi living in local soils may be one of the strongest indicators of how common childhood allergic diseases are in a region, according to new research to be presented at the American Geophysical Union’s 2025 Annual Meeting.
The study finds that soil microbial communities are more closely linked to rates of asthma, allergic rhinitis, and atopic dermatitis in children than factors such as wealth, demographics, or climate. While the research does not prove cause and effect, the association appears consistent across many parts of the world.
“We’ve tested this result in many different ways, and it keeps showing up,” said Joshua Ladau, a microbial ecologist at Arva Intelligence who led the research. “That consistency makes us very confident the link is real.”
Ladau will present the findings on 16 December at AGU25, which brings together more than 20,000 Earth and space scientists.
A global pattern
Allergic diseases affect an estimated 2.5 billion people worldwide, about 30% of the global population. Previous studies have suggested that exposure to a wide range of microbes in early life may help the immune system develop tolerance and reduce the risk of allergies. However, it has been unclear how important this exposure is compared with other influences such as health care access, pollution, or climate.
To explore this question, the research team analyzed data on more than one million children in over 250 cities across 97 countries. The health data covered the prevalence and severity of three allergic conditions: asthma, allergic rhinitis, and atopic dermatitis. These data were compared with three global surveys of soil bacteria and fungi, based on more than 8,200 soil samples.
Using statistical models, the researchers examined how strongly regional disease rates were associated with soil microbial patterns. Because soil samples were not always taken from the same exact locations as the health data, the team developed methods to account for distance between sampling sites.
Despite these challenges, the results were clear. Soil microbial communities emerged as the most important predictor of regional differences in asthma and allergic rhinitis, both in how common the diseases were and how severe they were. In the models, soil microbes were up to four times more predictive than the next strongest factor, including climate and socioeconomic measures.
Which microbes matter
The findings suggest that overall microbial diversity is not the key factor. Instead, the specific types of microbes present in the soil appear to matter most.
“It’s not that more microbes are always better,” Ladau said. “Some groups are associated with better health outcomes, and others are linked with worse ones.”
Notably, the microbes associated with higher allergy rates were not previously known pathogens, highlighting how little is still understood about the health roles of many soil organisms.
The researchers stress that the study shows correlation, not causation. It does not prove that soil microbes directly reduce allergic disease. However, no other measured factor explained the patterns as well as soil microbial composition.
Implications beyond health
Future research will focus on whether the relationship is truly causal and on ways to safely increase exposure to potentially beneficial soil microbes. Possible approaches include spending more time outdoors and adopting land management practices that protect and restore healthy soils.
Such efforts could have multiple benefits, Ladau said, including carbon storage, ecosystem recovery after fires, and pest control. If confirmed, links to human health would add another reason to protect soil ecosystems.
“Connecting soil biodiversity to public health highlights just how important soils and their microbial life really are,” he said.
