Using a dishwasher instead of washing dishes by hand could be making children more susceptible to allergies, a study suggests.

The findings, researchers suggest, are yet more support for what's being called the "hygiene hypothesis," which holds that children living in developed countries are growing up in a world that is increasingly over-sanitized, with anti-bacterial detergents and soaps and relatively little exposure to animals, preventing their immune systems from becoming exposed to and thus generating an immunity against many common bacteria.

When it encounters such microorganisms, some experts suggest, the immune system can "misfire" and can cause allergies and asthma.

In a study published in the journal Pediatrics, Swedish researchers report they found that children in families that hand-wash dishes display fewer allergic conditions.

That's in line with some earlier studies that found other early lifestyle factors such as having pets, eating fish or living on a farm were associated with a significantly lower risk of developing allergies.

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

The researches polled the parents of more than a thousand children ages 7 to 8 in two regions of Sweden on their children's allergies and how the family washed their dishes and how often they ate fermented or farm-fresh foods.

Children in families that hand-washed their dishes had significantly lower rates of allergies and eczema, and a slightly lower low rate of asthma, the researchers found.

Even after adjusting for other socioeconomic and lifestyle factors, "the associations between hand dishwashing and allergic diseases remain statistically significant for eczema and total allergy, whereas a borderline significance is seen for asthma," the researchers wrote.

The benefit was even seen in children too young to be hand-washing dishes, the researchers noted, suggesting instead the benefit came from long-term eating off of hand-washed dishes and cutlery containing more bacteria than those washed in dishwashing machines, which have proven more efficient at removing bacteria.

More research is needed to confirm the exact causal relationship between hand-washed dished and reduced allergies, Hesselmar says.

"It's an interesting finding and very surprising," he says. "But we have to see if we can confirm it."