Allergy Sensitivity
Doubles Since 1970s
More than half the population tests positive
in response to one or more allergens, double the percentage who
did 30 years ago, a new study reports.
Researchers at the National Institutes of
Health found that 54% of people tested positive to at least one
of 10 allergens. The highest response was to dust mites, 27.5%.
The lowest was to peanuts, 8.6%. The findings appear in the August
issue of the Journal of Allergy and Clinical Immunology.
Researchers analyzed data from skin-prick
allergy tests on 10,500 people by the Centers for Disease Control
and Prevention.
The number of positive reactions is much
higher than cases of actual allergic disease, notes lead researcher
Samuel Arbes of the National Institutes of Health. Though a positive
skin test for allergens such as ragweed or cats doesn't necessarily
mean a person has or will develop allergies, there is a strong
association between the two.
About 20% of U.S. residents have allergies
or hay fever; 8% to 10% have asthma.
The doubling of the prevalence of the six
allergens tested in the earlier survey corresponds to a period
during which there also was a 74% increase in asthma, Arbes says.
Though there is evidence asthma rates have peaked, allergy rates
appear to still be increasing, he says.
The testing was part of CDC's third National
Health and Nutrition Examination Survey from 1988 to 1994 and
is considered the most complete national data available to scientists.
The previous survey was from 1976 to 1980.
Those at highest risk of showing allergic
response were people ages 20 to 29, males, minorities, people
living in the West, people living in old homes and people who
were not exposed to cigarette smoke.
Skin tests involve applying an allergen extract
to skin, which is then lightly scratched. If the area swells,
the patient has antibodies to the allergen.
Researchers don't know why positive skin
tests, allergy and asthma are increasing. One theory is that people
simply don't go outside as often — Americans spend an estimated
90% of their time indoors — and have higher exposures to
indoor allergens.
Another theory is that children become more
vulnerable when they are exposed to fewer bacteria and viruses.
Some researchers believe that has an effect on the developing
immune system.
Reference
Source 129
August
9, 2005
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