In most farm children, asthma is not being prevented. And even in those children who might have had a benefit from being raised on a farm, it is not clear where the protection is mediated by: Some biological agent like endotoxin? Some healthy worker effect? Less medical interventions like antibiotics, Caesarean or vitamin D? It looks like other researchers are sceptical too
Others who study the hygiene hypothesis caution that the newly uncovered mechanism does not entirely explain the protective effect of dairy farm life. Drinking unprocessed milk also seems to ward off asthma in kids, points out Gary Huffnagle of the University of Michigan, Ann Arbor—and that effect is unlikely to involve the lung epithelium. What’s more, endotoxin levels are not that much higher on farms than in cities, suggesting “it’s too simple an answer,” says asthma genetics researcher William Cookson of Imperial College London, who thinks changes in living microbial communities in the lungs and gut may be just as important.