Children in hand-dishwashing homes had fewer allergies

Researchers at Queen Silvia Children's Hospital in Gothenburg surveyed 1,029 children aged seven and eight across two Swedish towns, asking parents in detail about how dishes were washed at home.

Children in households that washed dishes by hand had about 43 percent lower odds of developing allergic disease, including asthma, eczema, and hay fever, than children in households that used a dishwasher. The protective effect grew stronger in families that also ate fermented foods and bought food directly from farms.

The researchers favor the old hygiene hypothesis: a small amount of extra microbial exposure from imperfectly cleaned dishes may help train a young immune system to tell harmless substances apart from real threats. The study cannot prove cause and effect on its own, since it was a one-time parent questionnaire rather than controlled exposure, but the dose-response pattern across hand-washing, fermented food, and farm food strengthened the association.

A dirtier sponge, a calmer immune system.