A new study has found that a combination of early-life exposures – specifically indoor dampness, outdoor air pollution and the absence of a family dog, significantly influences the risk of developing asthma by the age of five.
The research by the national Environmental Influences on Child Health Outcomes (ECHO) consortium analysed data from 6,413 children born between 1987 and 2016 across nine diverse birth cohorts. It aimed to untangle how indoor home environments and outdoor air pollution work together during the critical first years of life.
They found that children exposed to higher average levels of PM2.5 from outdoor air in their first three years had a 49% increased risk of an asthma diagnosis. Similarly, those living in homes with a history of water damage or dampness had a 17% higher risk.
It was also found that, having a dog in the home during infancy provided some protection and was associated with a 19% reduction in asthma risk.
This reinforces the role of early life as a window of heightened susceptibility for lung development. The team point out that it also adds evidence to the ‘hygiene (or microbiome) hypothesis,’ which suggests that early exposure to dogs may help train the developing immune system away from allergic reactions. Dogs introduce a diverse array of microbes into the home environment. This exposure during infancy helps train the developing immune system, promoting tolerance and reducing allergic responses.
Exposure to low levels of bacterial endotoxin from dogs may also play a protective role.
Combined exposure was found to compound the problem. Children living in homes with both dampness and high levels of outdoor PM2.5 faced nearly double the risk of asthma compared to children in dry homes with low pollution.
Akihiro Shiroshita, a study author from Vanderbilt University School of Medicine. said: ‘Our research shows that to truly understand and prevent childhood asthma, we need to look at a child’s full environment—both the air they breathe outside and the conditions inside their home. Considering these factors together gives us a much clearer picture of what puts children at risk and how we can better protect them.’
The study found no significant link between childhood asthma and exposure to household cats or dust mite allergens, though the authors note data on dust mites was limited.
The full research can be read here.
Photo: Emily Whitehouse
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