An old saying says “a little dirt never hurt,” and it turns out a Swedish study observing families’ dishwashing habits may have found some benefit to a less efficient way of doing this household chore.
A study of 1,029 Swedish children ages 7 and 8 looked to see if dishwashing methods played any role in the development of allergic diseases. The research indicated that hand washing was associated with lower rates of asthma, eczema and hay fever.
The rates were further decreased if the families ate fermented foods (such as sauerkraut or cucumber) or bought foods directly from farms.
The study is the latest of many that indicate that the so-called “hygiene hypothesis” – how clean our environments are – play a role in the development of atopic, or allergic, diseases. The hygiene hypothesis speculates that environments that are too clean creates immune systems in children that are understimulated. The immune systems become, in a sense, “bored,” and start producing allergic responses.
In this study, published recently in the journal Pediatrics, families in two towns in Sweden filled out a questionnaire that asked very detailed questions about their lifestyle habits. Scientists analyzed their responses.
Researchers asked about their history of allergic diseases, such as asthma, eczema, and hay fever. Families also were asked about how they washed dishes, how they cooked, and how long children were breastfed. Other topics included day care, pets, and smoking.
The study found that a history of eczema was found in 23% of children whose parents washed dishes by hand, yet was 38% for families with dishwashers.
Likewise, families who washed dishes in the sink had an asthma rate of 1.7%, but for those who used dishwashers, it was 7.3%. There was a difference for hay fever, but it was not statistically significant. For total allergy rates (asthma plus hay fever plus eczema combined) buying food from a farm and eating fermented food seemed to offer a level of protection as well.
Since the development of the hygiene hypothesis, scientists have looked for other explanations as to why allergy rates are higher in the modern, industrialized world, since they can’t very well recommend that society return to living conditions common 100 years ago.
While researchers noted that the lack of dishwashing by machine may also be linked to low socioeconomic status, immigration status or overcrowded housing, the association between handwashing dishes and lower allergy rates remained even after accounting for those factors. However, one must always exercise caution when interpreting results from studies using surveys, as the medical diagnoses are by self-report and there is no way to prove any type of cause-and-effect relationship.
The study was published in the February 23, 2015 issue of Pediatrics.