Research shows that asthma and allergies are less common in children raised on farms than in children raised in other settings. One major difference between farms and other households is the farm animals, which are a source of bacteria and allergens. Similarly, research has suggested that having household pets very early in life may reduce the risk of developing allergies and asthma later in life. Such research has led some experts to question whether living in an environment that is “too clean” can make children susceptible to asthma and allergies.

To test this theory, Swiss, German, and Austrian researchers measured the levels of endotoxin—a substance present in the cell wall of some bacteria—in the bedding of children in farming and nonfarming households. Their research, published in the September 19, 2002 New England Journal of Medicine, suggests that children living on farms are indeed exposed to higher levels of endotoxin. But what’s more interesting is that children exposed to higher levels of endotoxin were less likely to develop asthma and allergies, regardless of whether or not they lived on a farm.

About the Study

Researchers from the Allergy and Endotoxin Study Team studied 812 children between the ages of 6 and 13 living in rural areas of Germany, Austria, and Switzerland. In this group, 319 children lived on farms and 493 did not.

Researchers used vacuums to collect samples of dust from the children’s mattresses. The dust samples were sent for laboratory testing of both their endotoxin levels and their allergen levels. In addition, the children underwent blood tests to measure levels of antibodies and other chemicals in their blood involved in allergic responses of the immune system.

The children’s parents completed a questionnaire about their type of household (farm or not) and any diseases and symptoms their children exhibited, including asthma and allergies (hay fever, itchy runny nose).

Researchers compared the number of asthma and allergy cases among children who lived on farms and children who did not live on farms. They also compared the asthma and allergy cases in children exposed to higher levels of endotoxin in their mattresses with children exposed to lower levels.

The Findings

As expected, children who lived on farms in their first year of life were less likely to develop asthma and allergies than children not living on farms. However, regardless of living on a farm, children whose mattresses contained higher levels of endotoxin were less likely to develop asthma or allergies than children with lower levels of endotoxin in their mattresses. In addition, blood tests indicated that children with higher endotoxin exposure (via farm or not) were less likely to have become sensitive to allergens than those with lower endotoxin exposure.

These findings were adjusted to account for other factors that may affect asthma and allergy risk, such as age, sex, family history of asthma or hay fever, number of older siblings, and parents’ education.

Although these results suggest that endotoxin in mattress dust is desirable, this study has its limitations. Because mattress endotoxin levels were only measured once between ages 6 and 13, the researchers were unable to determine exactly when during childhood endotoxin exposure may be protective. However, endotoxin levels in beds have been shown to remain fairly constant over time. In addition, the researchers did not measure the levels of other bacterial substances in the mattress dust. These other substances could play a role in building up immunity to common allergens. Finally, this study relied on parents to report whether their children had asthma or allergies. This method of collecting information is prone to error.

How Does This Affect You?

These findings support the idea that early exposure to allergens and infectious agents, such as bacteria, “primes” the human immune system so that it responds more appropriately to its environment. This does not mean, however, that we don’t need to clean our homes. But it does suggest, that there may be some advantage to growing up in less than immaculate surroundings.

If you have asthma or allergies, your health care provider has probably advised you to regularly clean bedding, curtains, and rugs to remove allergens such as dust mites and pet dander. In fact, you may be advised not to have household pets at all. This advice is still reasonable, because people who already have asthma or allergies can reduce flare-ups of symptoms by reducing exposure to their allergens. However, these new research findings support the belief of some medical experts that exposure to such allergens in early childhood may actually help prevent allergies and asthma from developing in the first place.

So, in an effort to reduce your young child’s risk of developing allergic conditions, it may be wise not to get rid of Fido or Fluffy, or to try to remove all traces of dust and allergens from your home. That strategy just might backfire on you.