People have only been sterilizing their dishes for about half a century. Water above 145 degrees Fahrenheit kills many bacteria. Dishwashers typically run between 130 and 170 degrees Fahrenheit, but people can get third-degree burns from 133-degree water in 15 seconds, according to the Burn Foundation. It would seem dishwashers are a safer option, but new research in the journal Pediatrics from Sweden’s University of Gothenburg suggests it may not be an entirely ideal solution.
Related: The best way to load a dishwasher, according to science
The university’s study followed 1,029 Swedish children, who were 7 and 8 years old, to see how hand washing and machine washing dishes affected them. Researchers found eczema was far less likely to develop in children whose parents did the dishes by hand, and allergic asthma and hay fever were somewhat less likely to occur in these children, too. The effect may be due to the hygiene hypothesis: the idea that those in developed countries aren’t exposed to enough bacteria and microorganisms, thanks to everything from sterilization to hand sanitizers to a lack of interaction with animals. In developing countries, such exposure helps immune systems learn what it should attack and what it should leave alone.
“The hypothesis was that these different dishwashing methods … are not equally good in reducing bacteria from eating utensils and so on,” Dr. Bill Hesselmar, who led the study, tells NPR. “So we thought that perhaps hand dishwashing was less effective, so that you are exposed to more bacteria.”
Of course, he admits that this could be correlation and not causation and other factors, such as the type of food eaten (fermented) and purchasing some items from a farm rather than a grocery store, also appeared to make the children in hand-washing families more immune.
While he says the study does lend support to the hygiene hypothesis, allergist Dr. Todd Mahr tells NPR that it’s too early to recommend dismantling the dishwasher. “I’m not convinced it’s going to make that big a difference,” he says of favoring hand washing.
