Clinical Question

Can the way dishes are washed affect the development of allergies in children?

Bottom Line

These results add further credence to the idea that the gastrointestinal system plays a big role in the development of our immune system (i.e., the hygiene hypothesis). Washing children's bottles and eating utensils by hand instead of using an automatic dishwasher was associated with a lower risk of developing an allergic disorder. The authors stop short of recommending low hygienic standards, but they suggest that fastidiousness might not allow the immune system to learn how to self-modulate. (Level of Evidence = 2b)

Synopsis

The goal of this wide-ranging study was to see whether exposure to microbes early in life affected the development of allergies. The Swedish investigators sent questionnaires to parents of 1,029 children, seven to eight years of age, in a single city, asking about each child's history of allergy, including any diagnosis of eczema, asthma, or allergic rhinoconjunctivitis, as well as asking about eating habits. To test for dietary microbes, the researchers asked parents about how they washed their dishes (using a dishwasher or by hand); their use of farm-purchased milk, eggs, or unpasteurized milk; whether their diet included fermented foods (e.g., sauerkraut) or home-cooked foods; and the duration of their breastfeeding.

Most of the children attended day care and one-third had a pet, but only 6% lived in a household in which a parent reported smoking inside. After analyzing all these factors to look for associations, hand dishwashing, which occurred in only 12% of households, was associated with the greatest reduced risk of allergic disease development (odds ratio = 0.57; 95% confidence interval, 0.37 to 0.85). The risk was further reduced in a dose-response pattern if the children were also served fermented food and if the family bought food directly from farms. The associations remained after adjusting for socioeconomic factors.

Study design: Cross-sectional

Funding source: Foundation

Setting: Population-based

Reference: HesselmarBHicke-RobertsAWennergrenGAllergy in children in hand versus machine dishwashing. Pediatrics2015; 135( 3): e590– e597.