SATURDAY, Nov. 13 (HealthDay News) -- It's a common belief that as you get older, your allergy symptoms will wane, but a new study suggests it's possible that even more older people will be experiencing allergies than ever before.

In a nationally representative sample of people, researchers found that IgE antibody levels -- that's the immune system substance that triggers the release of histamine, which then causes the symptoms of allergies like runny nose and watery eyes -- have more than doubled in people older than 55 since the 1970s.

IgE levels don't always directly correlate with the presence of allergies or consistently indicate their severity, but IgE is the main antibody involved in allergies, explained study author Dr. Zachary Jacobs, a fellow in allergy and immunology at Children's Mercy Hospital and Clinic in Kansas City, Mo.

"With IgE levels, it's hard to make an inference for a specific individual, but we're reporting a population trend, and it looks like there's increased allergic sensitization. It looks like Americans have more allergies now than they did 25 or 30 years ago," Jacobs said.

And, he added, "People in their 50s almost certainly have more allergy now than they did 25 or 30 years ago, and more allergists will be needed for the baby boomers."

The findings are to be presented Saturday at the American College of Allergy, Asthma and Immunology annual meeting, in Phoenix.

Jacobs and his colleagues noticed that no one had looked at levels of IgE in the population since the 1970s, when a large study called the Tucson Epidemiological Study was done.

The new study compared data from the Tucson study in the '70s to data from the more recent National Health and Nutrition Examination Survey (NHANES) from 2005 to 2006.

There were 7,398 people enrolled in NHANES, while the Tucson study included 2,743 people. The demographic profiles for the two studies were similar, although there were slightly more young people (under 24) in the NHANES study.

IgE levels, which are measured with a blood test, however, were not always the same. The Tucson study group had higher IgE levels in only one age group -- 6- to 14-year-olds. In all other age groups, the NHANES participants had significantly higher IgE levels.

The difference was most striking in the older age groups. For example, in those aged 55 to 64, IgE levels among NHANES participants were more than double those of the Tucson group.

Jacobs said his researchers didn't think better testing methods could account for this difference. If better tests were a factor, he said, the differences would have stayed the same across the ages, but in the younger group, IgE levels were lower in the NHANES study compared to the Tucson group.

Jacobs said there are numerous factors that could be at play, but all are hypotheses. He said the "hygiene hypothesis" is a popular theory. The hygiene hypothesis essentially means humans are now living in a world that's too clean, even wiping out good bacteria and leaving the immune system to fight off only the most harmless of foreign substances. Another possibility is the potential of global warming, which could be causing higher CO2 levels and more pollen, theoretically contributing to the rise in allergic disease, he said.

Dr. Jennifer Appleyard is chief of allergy and immunology at St. John Hospital and Medical Center in Detroit. She said: "The common wisdom is that IgE production typically drops as you get older. So, to see a general trend like this is surprising."

"IgE reflects much more than just allergy. It can be affected by many things, like smoking, parasitic diseases and eczema. So it's not just affected by or represented by allergy, and levels of IgE aren't directly correlated with severity of disease. But this study's findings are interesting, and definitely bear further evaluation," Appleyard added.

More information

Learn more about allergies from the U.S. National Library of Medicine.