Most parents want their children to live in an environment that's clean and sanitary. We all buy home appliances that allow us to keep our homes as spotless as possible with little effort.
But increasingly, research indicates that a little bit of dirt and bacteria may be a good thing. The newest study to lend support for the so-called "hygiene hypothesis" finds children are less likely to have allergies if they live in homes where dishes and food utensils are washed by hand rather than in a dishwasher. The hygiene hypothesis is the idea that early exposure to an array of different microbes is needed to help a child develop a healthy immune system.
"The whole idea is that humans and all mammals live in homeostasis with all their bacteria in their lungs, skin and GI tract," David Rosenstreich, chief of the division of the allergy and immunology at the Albert Einstein College of Medicine and Montefiore Medical Center, told CBS News. "Having a lot of different bacteria growing inside you tends to stimulate the immune system and makes things stronger."
The new study, published Monday in the journal Pediatrics, involved 1,029 children aged 7 and 8 from Sweden. Families filled out questionnaires about their children's history of asthma, eczema and rhinoconjunctivitis (mucous membrane inflammation that causes itchy and watery eyes and congested sinuses).
The researchers found that children living in homes where dishes were done the old-fashioned way -- by hand with a sponge -- were far less likely to have these common allergic conditions.
The researchers found that a history of eczema was reported in 23 percent of children of parents who hand-washed dishes versus 38 percent in those who primarily used a dishwashing machine in their home. With asthma, 1.7 percent of children in hand-washing homes had asthma, compared to 7.3 percent of children in homes that used dishwashers. Approximately 10 percent of children in hand-washing homes, versus nearly 13 percent in dishwasher homes, had a history of rhinoconjunctivitis.
The rate of allergies was even lower for children who also ate fermented foods at home as well as food bought directly from farms, which may have exposed them to a greater diversity of microbes. One-third of children exposed to those foods in addition to hand-washed dishes suffered from allergies, compared to 46 percent of children in the families that used dishwashing machines and didn't consume such foods.
However, the concept of hygiene hypothesis is much more complex than it's often made out to be. "In different countries and settings, different risk factors and protective factors for asthma and allergy seem to interact, and the effect of this interaction on a specific individual depends on their genetic/epigenetic susceptibility," the researchers write in their study. "We know, for example, that early day care attendance may protect against sensitization, but only in children without siblings."
In the last decade or so, interest has emerged in research on the microbiome, the composition of "good" versus "bad" bacteria that naturally reside in our bodies. The composition of the microbiome has been associated with obesity, autoimmune disease, depression and fetal development.
The researchers in the latest study suggest that hand-washing kitchenware exposures children to a more diverse microbiome, which may help to boost their immune system in positive ways.
"What's nice about it is it's something everyone can do," said Rosenstreich, who was not involved in the study. "Obviously GE isn't going to be happy about it."