Washing Dishes by Hand Linked to Fewer Allergies

Laura Putre

February 24, 2015

Washing dishes by hand, rather than in a dishwasher, may help prevent allergies in children, a new Swedish study has found. In addition, the study suggests that consuming fermented or farm-bought food could decrease the likelihood of allergies further.

The study, published online February 23 in Pediatrics, analyzed questionnaire responses about daily household practices from families of 1029 children aged 7 to 8 years.

Bill Hesselmar, MD, PhD, from Queen Silvia Children's Hospital in Gothenburg, Sweden, and colleagues found that overall, allergies were less common in children from families who primarily hand-wash their dishes than in families who primarily use a dishwasher.

The researchers theorized that the bacteria left over on dishware and utensils from hand-washing, a "less-efficient dishwashing method," helped the subjects build tolerance to allergens.

"Low hygiene standards and increased microbial exposure are common denominators often seen in low allergy-risk settings," the authors noted.

Twenty-three percent of children from families who washed dishes by hand had a history of eczema compared with 38% from families who mainly used dishwashers. Only 1.7% of children in hand-washing families had asthma compared with 7.3% in families with dishwashers.

The difference was smaller for nasal allergies: 10.3% in hand-washing households vs 12.9% in dishwasher households.

Eating fermented (probiotic-rich) food such as sauerkraut and fermented cucumber and buying food from farms did not, on their own, make a significant difference in allergies. But when combined with hand-dishwashing, these practices coincided with an overall reduction in allergies, the researchers found.

Forty-six percent of children suffered from allergic diseases in families that used machine dishwashing, did not buy food directly from farms, and did not eat fermented food. Comparatively, only 19% of children from families that hand-washed dishes and practiced at least one of the other two protective behaviors experienced allergies.

An accompanying editorial by Laurence E. Cheng, MD, PhD, and Michael D. Cabana, MD, MPH, from the University of California, San Francisco, stated that the research, although interesting, "has definite limits," leaving many unanswered questions.

For instance, why would the effects of contact with residual microbes on utensils be more powerful than actually ingesting fermented or farm-bought food? Analyzing the amount and make-up of microbes on utensils after hand-washing and less-than-sanitary storage techniques could prove illuminating, the editorialists advise.

"Much more clinical, translational and basic studies are needed to elucidate the role of different lifestyle choices...and microbial exposures," they state, "and how those microbial exposures may modulate allergic disease and potentially lead to a primary prevention strategy."

The children in the study hailed from two Swedish cities: Kiruna in the north and Mölndal on the southwest coast. The questionnaire was from the International Study of Asthma and Allergies in Childhood, used to estimate the prevalence of asthma, nasal allergies, and eczema.

The Swedish researchers called for more investigation into the link between immunity and household practices. They acknowledged limitations in their research, including the fact that the questionnaire did not ask how long the families had been practicing their current method of dishwashing. Also blurring the findings, they write, was the fact that hand-washing may coincide with other lifestyle factors, such as living in close quarters, that can play a role in immunity.

The authors have disclosed no relevant financial relationships.

Pediatrics. Published online February 23, 2015. Full text

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