Cleanliness may be next to godliness, but obsessing over hygiene may not be healthy practice, research suggests.

A new European study looked at over 800 children age six to 13. Researchers found kids who lived in the dustiest environments were less likely to suffer from asthma and hay fever.

Growing up on a farm and being exposed to animal dander, ragweed and dirt may protect the health of children, according to a scientific theory called the hygiene hypothesis.

Farm kids had a lower incidence of asthma

The theory suggests our immune systems aren't fully developed at birth, and we're primed to develop allergic reactions. Germs may mature the immune system against allergies, much as vaccines protect against disease.

"As kids acquire infections during the course of childhood, then it resets the immune system towards dealing with infections and away from the allergy mode," said immunologist Dr. Peter Vardas of St. Michael's Hospital in Toronto.

A research team led by Charlotte Braun-Fahrlander of the Institute of Social and Preventive Medicine in Basel, Switzerland, found children raised in the cleanest conditions faced a greater risk of developing hypersensitivity to substances that trigger allergic reactions.

The study in Thursday's issue of the New England Journal of Medicine found farms offer one of the best places for the immune system to be exposed to infection.

• FROM AUG. 27, 2002: Infants raised with cats, dogs show lower allergy risk: study

Soil and animals on farms are teeming with endotoxins – microscopic substances released by bacteria as they die.

Vacuuming bedrooms to study dust

Parents of children living in rural areas of Germany, Austria and Switzerland were questioned about their children's health problems, and the kids were tested for allergic sensitivity.

Researchers measured exposure to endotoxins by vacuuming the childrens' beds and analyzing the dust.

They found kids with the dirtiest bedding had the lowest rates of asthma and hay fever.

Asthma Quick Facts Asthma is the most common chronic respiratory disease in children Asthma accounts for one quarter of school absenteeism Peak period for asthma in Canada tends to be the third week of September Sources: Lung Association of Canada, Firestone Institute for Respiratory Health

Some allergy specialists say North America's obsession with cleanliness and antibacterial cleaning products may be driving our higher rates of allergy and asthma.

"Don't get crazy about having antibacterial wipes around all the time," said pediatric allergist Dr. Sandeep Kapur in Halifax. "Realize that some exposure to germs in life is not bad, it's actually good."

But there's also a tradeoff, because children are more likely to develop infections in unhygienic environments. And kids who already have allergies or asthma should avoid whatever triggers them.

The study's authors don't recommend parents let their kids eat dirt or move to a farm to prevent asthma and allergies. Instead, they suggest we all relax about cleaning to the point of making the environment sterile.