A study published on Monday by the journal Pediatrics has gotten a lot of press this week because it shows a connection between allergies in children and the method by which parents wash their dishes. Parents, especially new parents, often consider good hygiene as one of the most important factors in raising their new child, but according to the hygiene hypothesis it may be true that too much cleanliness actually negatively affects a young child. Asthma, eczema, and other autoimmune diseases are becoming more common conditions in children, and each has been linked to the hygiene hypothesis. Researchers in Sweden reinforced this link when they discovered a possible connection between allergies in children and whether dishes were washed by hand (less clean) or by machine (more clean) in their homes.
The researchers sent a questionnaire to parents of children aged 7-8 which was filled out by 717 families in Molndal, Sweden and 312 families in Kiruna, Sweden. The questionnaire asked many questions pertaining to the children, including previous symptoms of asthma or eczema, method of washing dishes, and if their food was farm grown or fermented. When examining the results it is important to remember that all forms of bias cannot be eliminated when doing surveys, because, among other reasons, it is difficult to get a perfectly random sample.
Results of the study showed that there were lower instances of allergies in children whose families washed their dishes mainly by hand rather than by machine. In addition, this effect was amplified if the children ate food that was either fermented or purchased from a farm (both of which should introduce diverse bacteria to the children). Of course, there were other variables that were not inquired in the questionnaire that are also known to decrease rates of allergies in children, and which may be related to washing dishes by hand, for example a lower socioeconomic status. Then again, the authors suggest that hand washing dishes may reasonably be responsible for these lower rates of allergies in children of lower socioeconomic status.
So, you may be wondering how exactly this pertains to the microbiome. Hand washing dishes cleans less thoroughly than highly efficient machines, which sounds gross, but the exposure to more microbes when you are young may help develop the microbiome and immune system. While this study is not perfect, it still shows us that exposure to bacteria is potentially a good thing for the new and developing microbiome.