According to a study, households where dishes are washed by hand have children less susceptible to developing allergies.

In a study published in the journal Pediatrics, researchers explored further the "hygiene hypothesis" where it is suggested that getting a little bit dirty is good for the immune system. Given the hypothesis, it is then speculated that the reason so many children today develop a lot of allergies is because they are living in environments that are too clean. Having not been exposed to bacteria early in their life, the children did not develop hardy immune systems as they should.

"We thought [hand washing dishes] might be important, but we didn't know, so we asked that question," said Bill Hesselmar, one of the authors for the study.

The researchers surveyed guardians and parents in households with children between the ages of 7 and 8. More than a thousand children were involved in the study and the researchers found that just 23 percent of children in hand-dishwashing households had a history of eczema while 38 percent of those in machine-dishwashing families had the condition. The results were also amplified when children ate fermented food or items directly bought from farms like unpasteurized milk, meat and eggs.

Hesselmar and colleagues don't confirm causality but they have a possible explanation for the results. Children are not exposed to bacteria during dishwashing because they don't do the chore themselves. Rather, they are using dishes that have been hand-washed.

Even with the use of dishwashing soap, hand-washed dishes are left with more bacteria compared to those machine-washed. Children in households hand-washing dishes then have more opportunities to be exposed to bacteria, which gives them stronger immune systems.

At the same time, hand-washing households also generally practice lifestyles that contribute to lower allergy risk. Researchers also noted that immigration status, low socioeconomic standing and overcrowded housing have links to fewer allergies. Fermented food, for instance, contains beneficial probiotic bacteria so eating some regularly establishes good gut flora that helps maintain health.

Further research, however, will have to be made to determine why exactly hand-washing dishes leads to fewer cases of allergies in children and why the lower number is mostly associated with instances of eczema and not other allergy-related symptoms such as asthma.

Other authors include: Göran Wennergren, M.D., Ph.D. and Anna Hicke-Roberts, M.D. Hesselmar and Wennergren are associated with the Queen Silvia Children's Hospital and University of Gothenburg's Department of Pediatrics while Hicke-Roberts is from the Västra Frölunda Pediatric Outpatient Clinic.