Allergens
are widespread, but highly variable in U.S. homes, according to the nation's
largest indoor allergen study to date. Researchers from the National Institutes
of Health report that over 90 percent of homes had three or more detectable
allergens, and 73 percent of homes had at least one allergen at elevated
levels. The findings were published November 30 in the Journal of Allergy
and Clinical Immunology.
"Elevated
allergen levels can exacerbate symptoms in people who suffer from asthma and
allergies, so it is crucial to understand the factors that contribute,"
said Darryl Zeldin, M.D., senior author and scientific director at the National
Institute of Environmental Health Sciences (NIEHS), which is part of NIH.
Using
data from the 2005-2006 National Health and Nutrition Examination Survey
(NHANES), the researchers studied levels of eight common allergens - cat, dog,
cockroach, mouse, rat, mold, and two types of dust mite allergens - in the
bedrooms of nearly 7,000 U.S. homes.
They
found that the presence of pets and pests had a major influence on high levels
of indoor allergens. Housing characteristics also mattered - elevated exposure
to multiple allergens was more likely in mobile homes, older homes, rental
homes, and homes in rural areas.
For
individual allergens, exposure levels varied greatly with age, sex, race,
ethnicity, and socioeconomic status. Differences were also found between
geographic locations and climatic conditions. For example, elevated dust mite
allergen levels were more common in the South and Northeast, and in regions
with a humid climate. Levels of cat and dust mite allergens were also found to
be higher in rural areas than in urban settings.
To
provide a more complete picture, the research team also compared allergen
exposure and previously reported sensitization patterns from this survey.
Sensitization, which makes a person's immune system overreactive to allergens,
may increase the risk of developing allergies and asthma. NHANES 2005-2006
allowed national level comparisons of exposure and sensitization for the first
time.
The
team uncovered several differences. Although males and non-Hispanic blacks were
less likely to be exposed to multiple allergens, sensitization was more common
in these groups, compared to females and other racial groups, respectively.
Patterns also differed for urban and rural settings. Exposure to several
elevated allergens was most prevalent in rural areas, whereas sensitization
rates were shown to be higher in urbanized areas.
Overlaps
were also found. For dust mite allergens, exposure and sensitization was most
prevalent in the Southern and Northeastern regions, and for cockroach allergen
in the South. Patterns also reflected socioeconomic variations, especially for
pet and cockroach allergens, according to lead author Paivi Salo, Ph.D., of
NIEHS.
The
researchers emphasized that the relationships between allergen exposures,
allergic sensitization, and disease are complex. Studies are still
investigating how allergen exposures interact with other environmental and
genetic factors that contribute to asthma and allergies.
In
the meantime, the following preventive actions may help reduce exposure to
indoor allergens and irritants.
- Vacuuming carpets and upholstered furniture every week.
- Washing sheets and blankets in hot water every week.
- Encasing mattresses, pillows, and box springs in allergen-impermeable covers.
- Lowering indoor humidity levels below 50 percent.
- Removing pets from homes or at least limiting their access to bedrooms.
- Sealing entry points and eliminating nesting places for pests, as well as removing their food and water sources.
"Asthma
and allergies affect millions of Americans," said Salo. "We hope this
comprehensive study provides beneficial information to a wide audience, from
patients to clinicians."
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