Air-tight homes may be fueling rise in allergies

Washington -- Allergies may be poised to affect even greater numbers of people, and could increase vulnerabilities to asthma, hay fever and eczema.

Findings based on data from the third National Health and Nutrition Examination Survey (NHANES-III) show that more than 54% of 6- to 59-year-old participants tested positive to at least one allergen, with reactions to dust mite, rye, ragweed and cockroach allergens the most common. Reactions to peanut allergens were least common.

In addition, the researchers found that the number of positive skin tests had greatly increased since an earlier survey, NHANES-II, was conducted.

The large NHANES nationally representative surveys are conducted periodically by the Centers for Disease Control and Prevention to assess the health and nutritional status of the U.S. population. These most recent findings, sponsored by the National Institute of Environmental Health Sciences and the National Institute of Allergy and Infectious Diseases, were published in the August Journal of Allergy and Clinical Immunology.

No one really knows why allergies and asthma are on the increase, although there are a number of theories. But their rise could mean more than runny noses and sneezing and could be connected to the recent increase in the number of people with asthma, said the researchers.

"Asthma is one of the world's most significant chronic health conditions," said NIEHS Director David A Schwartz, MD. "Understanding what may account for the rising worldwide asthma rates will allow us to develop more effective prevention and treatment approaches."

Figures from the National Center for Health Statistics indicate that the number of asthma cases in the United States jumped by 74% from 1980 to 1996.

Adding to that evidence, the CDC reported Aug. 12 that one in six high school students said they have asthma and more than one in three reported they had had an attack during the preceding year.

The researchers were cautious to temper their findings by indicating they had examined positive responses to allergens rather than full-blown allergies. However, the findings do correspond with studies from other countries, such as Japan and the United Kingdom, indicating rising rates of allergies, said NIEHS Epidemiologist Samuel J. Arbes, DDS, PhD, MPH, lead author on the study.

Searching for answers

As for why allergies and asthma are on the rise, a look under the bed may reveal all. At least that's what Dr. Arbes hopes will happen when the ongoing NHANES survey analyzes for allergens samples of dust from the homes of 10,000 survey participants. Blood samples taken from the residents of the homes will also be analyzed for antibodies to those allergens.

The dust analysis is a new component for the NHANES survey, and it is expected to enable researchers to gain a greater understanding of the role played by indoor allergens in provoking asthma and other allergic diseases.

Indoor allergens are already regarded as prime suspects in the growth of the legions of allergic people. Children playing computer games among billions of dust mites in homes that are newly energy efficient and sealed tightly may well increase their risk of allergies, many speculate.

"Children don't go out to play," said Kathleen Sheerin, MD, an allergist in private practice in Atlanta. "We do know that wall-to-wall carpets have made dust mites more of a problem. Mice are a new, up-and-coming allergen in the home, and there are cockroaches in suburbia."

Indoor allergies also persist throughout the year. "When you mention allergy to people, they say 'I'm not sneezing and don't have a runny nose when all the pollen is out.' But they have symptoms all year round and you find out it's their dog or cat, dust mites or mice."

"We are appreciating that people are having symptoms throughout the year and that persistent symptoms are most likely to be caused by indoor allergies," said Leonard Bielory, MD, director of the asthma and allergy research center at the University of Medicine and Dentistry of New Jersey.

Speculation also centers on the so-called hygiene hypothesis as a reason for the increase in allergies and asthma. Although far from proven, the theory holds that the modern quest for cleanliness has meant that immune systems are no longer exposed to as many germs and allergens at an early age. Exposure later in life seems to be more problematic.

"We don't eat that Oreo that fell on the floor. We take too many antibiotics and we lead too clean an existence," said Dr. Sheerin. "We need a cow in the front yard."

Jacqueline Pongracic, MD, who heads the allergy division at Children's Memorial Hospital in Chicago, isn't surprised that more than half of the population is likely to test positive for some allergen. She sees the crowded waiting room and reads the literature about increasing rates of asthma.

Although the studies have been done that show an exacerbation of asthma among children who already have the disease and are exposed to indoor allergens, the question is whether something can be done before the onset of asthma or an allergic sensitivity develops, she said.

"That study hasn't been done yet, but that's the big question that a lot of people are interested in."

As for the look at dust under the bed, "It's long overdue," said Dr. Bielory.