A study by Swedish researchers has found conditions like asthma, eczema and hay fever are less common in households practising ‘less efficient’ hand-washing

Hand-washing your dishes may not sanitize as well as a dishwasher, but it may correlate with a lower risk of allergies in your children, Swedish researchers said in a new study released on Monday.

The scientists believe the dishwashing method introduced children to more microbes, helping develop their immune systems, and leading to less autoimmune disorders such as asthma, eczema and what is commonly called hay fever (a runny nose, itchy eyes, coughing and sneezing). The study was published in the Journal of the American Academy of Pediatrics.

“The importance of this finding is that in affluent countries there are common lifestyle factors with an individual impact that may affect the risk of allergy development in children,” the three Swedish researchers said.

The study surveyed 1,029 Swedish households of seven- and eight-year-old children, asking about allergies and lifestyle. Respondents gave information about whether they fed their children home-cooked meals, breastfed, gave children fermented foods, bought groceries from farms and whether they used a dishwasher.

The “less efficient dishwashing method”, as researchers called it, “may induce tolerance via increased microbial exposure”. Researchers also saw a positive correlation between serving fermented and farm-bought food and a reduction in allergies.

Fast food and takeaways linked to surge in child asthma and allergies Read more

The effectiveness of hand-washing dishes varies widely. In past studies, scientists have found that water temperature, type of gunk being washed off, utensil shape and technique all influences how clean dishes come out, making it difficult to generalize how much bacteria hangs around on hand-washed dishes.

What scientists seems clear on is that machines disinfect better than people. A 1947 study of 1,000 New York restaurants found that even using 1940s-era technology, dishes were significantly cleaner when put through a machine.



The new study expands upon hygiene hypothesis, a theory first posited in a 1958 study of British children to explain the higher incidence of allergies and autoimmune disorders found in children in developed countries. In other words, exposure to microbes now may help protect against disorders later.

The study released on Monday acknowledged that a number of lifestyle factors could have contributed to lower allergy rates, and that the study has limitations.

For example, living on a farm, crowded households, immigration status and low socioeconomic status all have an inverse correlation with allergies. People who fit into those categories are less likely to be allergic, but establishing a causal link between those factors and lower allergies is difficult.

Researchers said there was a “statistically significant” correlation between allergies and dishwashing, but also pointed out that families without dishwashers could be in lower socioeconomic positions. That sort of relationship is called a confounding factor.

A similar relationship arises from the lower allergy rates on farms. People who live on a farm are exposed to more microbes by virtue of where they live, and are more likely to drink unpasteurized milk, thus exposing them to more microbes. So is it the unpasteurized dairy or where people live that makes them less likely to have allergies?

The researchers also acknowledged the limitations of the study’s methods. More than 1,800 surveys were mailed, and 56% were returned. There could be a certain bias among the people who returned the surveys.

“However, such findings are mainly of interest from a theoretical point of view only,” said researchers, “as living on a farm is not a practical recommendation for allergy prevention.”