Too clean? Study suggests that germs in dust can protect against allergies

<br>BOSTON (AP) _ Got allergies? Asthma? Maybe you should blame Mom for keeping such a clean house. <br><br>A surprising European study suggests that germs in household dust can actually help protect children

Wednesday, September 18th 2002, 12:00 am

By: News On 6

BOSTON (AP) _ Got allergies? Asthma? Maybe you should blame Mom for keeping such a clean house.

A surprising European study suggests that germs in household dust can actually help protect children from developing hay fever or asthma.

The findings, published in Thursday's New England Journal of Medicine, counter decades of conventional wisdom. Doctors and parents long assumed that since dust can aggravate existing allergies, it can probably make a growing child more susceptible to developing them in the first place.

But about 10 years ago, doctors started seeing suggestions that dirt might actually be good for children.

``When it was first proposed, it seemed kind of ridiculous,'' said Dr. Norman Edelman, a respiratory specialist for the American Lung Association. ``We had been teaching people that a clean environment was better.''

The theory is known as the hygiene hypothesis. It holds that early contact with some germs arms the maturing immune system against some allergic conditions, much as vaccines protect against disease.

Some research, in fact, has suggested that children who are exposed early on to pets or to lots of other youngsters at day care are less likely to get colds or allergies later on.

Supporters of the theory suspect that indoor plumbing, cleaner and more airtight homes, and antibiotics have contributed to an explosion in allergies in industrialized countries.

The U.S. asthma rate rose about 74 percent between 1980 and 1996 but decreased slightly by 1999, the most recent year available, according to the Centers for Disease Control and Prevention. About 10.5 million Americans have asthma, and 24.8 million have hay fever.

The European researchers examined whether farm children in Switzerland, Austria and Germany _ who are exposed to lots of germs from animal waste _ have lower levels of asthma or other allergic conditions than other children. The researchers checked health histories and measured bacterial levels in dust in the bedding of 812 children.

They found about double the endotoxins _ bits of bacterial cell walls from farm animals and other sources _ in the bedding of farm children.

Just 3 percent of farm children had the common type of asthma known as atopic and 4 percent had hay fever. In other households, 6 percent had atopic asthma and almost 11 percent hay fever. Exposure to farming in the first year of life was especially protective.

Whether on farms or not, though, higher levels of germs were associated with lower risk of certain allergic conditions. Children with heavy germ exposure from bedding dust had about half the risk of atopic asthma and 60 percent the risk of hay fever, compared with youngsters who had low exposure.

``It may be through these environmental endotoxin exposures you get activation of the immune system _ without getting an illness,'' said one of the researchers, Dr. Erika von Mutius, a pediatrician at Dr. von Hauner Children's Hospital in Munich, Germany.

Several doctors said it is too soon even to consider recommending any lower sanitary standard. They warned that dust and animal dander can clearly worsen existing allergies. And some germs, of course, can make children dangerously sick.

``I wouldn't go home and say, `Gee, I'll let the baby sleep with the cat or in dust,''' said Dr. Leonard Bielory, an allergist at the University of Medicine and Dentistry of New Jersey. ``I know a certain exposure is beneficial. The dose and duration is unknown.''

However, he said the findings do suggest that children should be vaccinated only against potentially life-threatening diseases.