Parents who wash dishes by hand, instead of in a dishwasher, are less likely to have kids with allergies, according to a new study from Sweden.
While the researchers can't say avoiding dishwashing machines prevents childhood allergies, they suggest that bacteria left on hand-washed plates may teach the body to tolerate its environment.
Other studies have suggested that growing up on farms and living in developing countries reduce a child's risk of allergies, the researchers wrote in the journal Pediatrics.
The study's lead author told Reuters Health by email that while those earlier findings are interesting, they can't realistically be used to reduce allergies among children. For example, you can't tell parents to buy a farm.
"We are trying to find sources of 'harmless' microbial exposures in daily life that may be good enough to reduce allergy in children who are otherwise not exposed to a rich microbial flora in the same way as farm-living children," said Dr. Bill Hesselmar of the University of Gothenburg.
Hesselmar and his colleagues analyzed data from a 2007 survey of Swedish parents of 1,029 children ages seven and eight.
About 12 per cent usually washed dishes by hand; 84 per cent usually used a dishwashing machine.
About 23 per cent of children from homes where dishes were hand-washed had eczema, a skin inflammation usually brought on by an allergy. The same was true for 38 per cent of kids whose parents who usually used a dishwasher.
Similarly, about 2 per cent of kids in homes with hand-washed dishes had asthma, compared to about 7 per cent of kids using machine-washed dishes.
Even after accounting for other factors that may influence allergies among kids, the researchers found that those who lived in homes with hand-washed dishes were less likely to have allergies.
Overall, washing dishes by hand was tied to a 43 per cent reduced risk of allergies.
Using fermented foods and buying directly from farms strengthened the link, according to the researchers.
In an editorial, Drs. Laurence Cheng and Michael Cabana from the University of California, San Francisco note that several questions still need answers.
For example, why does washing dishes by hand appear to protect more against skin conditions than against itchy eyes and running noses? And for the most part, the researchers would have to assume that parents' dishwashing habits remained unchanged since the children's infancy for the hygiene hypothesis to be applicable.
"Future recommendations may be based on these findings, but only if the results could be confirmed in new studies," Hesselmar said.