To continue the theme of allergies (one of the recent AOTWs was about decreasing peanut allergy by introducing peanuts early) – the latest Pediatrics has an interesting study entitled “Allergy in Children in Hand Versus Machine Dishwashing”.

In a nutshell: risk of allergic disease was reduced in kids where hand washing (not machine dishwashing) was used, and this effect was amplified by eating foods that were fermented (e.g. sauerkraut) and food bought directly from farms.

The details:

Hypothesis: hygiene hypothesis stipulates that microbial exposure in early infancy induces immunologic tolerance via immune stimulation and reduces allergies. Hand dishwashing increases microbial exposure compared to machine dishwashing.

Methods: Observationaly study; Swedish version of the International Study of Asthma and Allergies in Childhood questionnaire sent to parents of 7-8 year olds in 2 towns in Sweden – questions about what form of dishwashing was used, if the child eats fermented food, food from a farm, home-cooked foods during 1st year of life, and length of breastfeeding.

Allergic disease: eczema, asthma or allergic rhino conjunctivitis

Results: 56% response rate (n = 1354 returned). Hand dishwashing was associated with statistically significant decr. in eczema (23% vs 38%) and asthma (1.7% vs 12.9%) but not allergic rhino conjunctivitis, even with controlling for variables such as daycare, parental allergies, crowding, smoking in pregnancy. Eating fermented food and food directly from farms decr. overall allergy risk, not specific allergic diseases.

Limitations: recall bias, only 56% response rate, parental report of disease diagnoses, specifics like how often hand washing was used were not asked, exposure and outcome do not equal causation in observational studies