Here’s another reason for children to do their chores: washing dishes by hand boosts children’s immune system. The findings were reported by Swedish doctors who found that in households where dishes are washed by hand children have much fewer allergic incidents than in those where the dishes are washed by a machine.

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Yet again, the findings serve to support the so-called “hygiene hypothesis” which says that the critical post-natal period of immune response is derailed by the extremely clean household environments often found in the developed world. In other words, the young child’s environment can be “too clean” to pose an effective challenge to a maturing immune system. For instance, over the years study have shown that environmental factors like pets, eating fish or living on a farm greatly boosts a child’s immune system. Of course, that’s not to say that kids living in the wilderness are necessarily healthier, but “bubble kids” are definitely at risk and parents should seek for a balance. Bacterial exposure needs not be inherently bad – it makes the kid stronger in later life!

“If you are exposed to microbes, especially early in life, you stimulate the immune system in various ways and it becomes tolerant,” says study author Dr. Bill Hesselmar of Queen Silvia Children’s Hospital in Gothenburg, Sweden for TIME. “We thought [hand washing dishes] might be important, but we didn’t know, so we asked that question.”

To quantify the effects of dish hand washing, the Swedish researchers surveyed the parents and guardians of 1,029 Swedish children ages 7 to 8. They found 23% of children whose parents used hand dishwashing had a history of eczema, compared with 38% of kids whose families mainly used machine dishwashing. Moreover, when children also ate fermented food or food bought directly from farms, these effects were amplified.

Of course, this is an observational study, not a causal one. Based on these clues, though, the Swedish researchers have some ideas why this is better. Previous work has found that dish washing machines are a lot more efficient and leave much fewer bacterial traces on dishes than those cleaned by hand. So, it’s not that the kids are washing the dishes themselves that’s boosting the immune system – most of them are too young to do it anyway – but rather, it’s that they’re eating off hand washed plates. But don’t tell your kids that if you still want them to do their chores.

“The study was really well done and caveated well, while simultaneously suggesting new areas of research and interesting models,” says Jonathan A. Eisen for TIME, a professor at the University of California at Davis. Eisen, who was not involved in the study.

This was a preliminary study published in the journal Pediatrics.