The hygiene hypothesis stipulates that microbial exposure during early life induces immunologic tolerance via immune stimulation, and hence reduces the risk of allergy development. Several common lifestyle factors and household practices, such as dishwashing methods, may increase microbial exposure. The aim of this study was to investigate if such lifestyle factors are associated with allergy prevalence.
Questionnaire-based study of 1029 children aged 7 to 8 years from Kiruna, in the north of Sweden, and Mölndal, in the Gothenburg area on the southwest coast of Sweden. Questions on asthma, eczema, and rhinoconjunctivitis were taken from the International Study of Asthma and Allergies in Childhood questionnaire.
Hand dishwashing was associated with a reduced risk of allergic disease development (multivariate analysis, odds ratio 0.57; 95% confidence interval: 0.37–0.85). 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.
In families who use hand dishwashing, allergic diseases in children are less common than in children from families who use machine dishwashing. We speculate that a less-efficient dishwashing method may induce tolerance via increased microbial exposure.