A Swedish study in the Journal Pediatrics in 2015 found that children from households that hand-washed dishes were at a lower risk of allergic disease (asthma, eczema, atopy) than those children who grew up in households with dishwasher appliances. The risk of allergy was further reduced in those children who consumed fermented foods and if the family bought foods directly from the farm.
The study was seen to reinforce the Hygiene Hypothesis – which stipulates that microbial exposure during early life induces immune system tolerance via immune stimulation, and hence reduces the risk of allergy development. In short, enough exposure to germs to mature the child’s immune system, but not enough to cause infectious disease. Both a diverse gut microbial flora and an altered oral microbial flora are associated with reduced rates of eczema and atopy. Some of the exposures studied in the context of the ‘hygiene hypothesis’ that are thought to mature a child’s immune system and create tolerance:
- vaginal birth as it increases microbial diversity
- breast-feeding, baby is exposed to mom’s skin and local flora
- parental cleaning of a child’s pacifier by sucking it
- having pets early in life
- living on a farm
- playing outside, in dirt
- having siblings or early childcare (in those without siblings). Several studies have demonstrated that infections during childhood may prevent later development of allergy
- eating fermented foods – sauerkraut, kombucha, home-fermented yogurt/kefir, kimchi, miso
- eating produce fresh from the garden
- discouraging antibacterial soaps, cleansers, cleaning agents
- limited use of antibiotics