Researchers have searched the U.S. and found that there's no place to go that's completely allergy-free.
In the new study published in The Journal of Allergy and Clinical Immunology, researchers gave blood tests to 8,124 people, including 856 children. They then scanned the blood for immunoglobulin E antibodies (IgEs), which can be an indicator of an allergy to a certain substance. Afterward, they tested them for antibodies to a number of different common allergens, such as peanuts, pets, ragweed, grass and shrimp.
The findings indicated that the prevalence of allergies did not vary across regions. It found that 45 percent of people over the age of six and 36 percent of children between one and five were allergic to at least one of the allergens. There were also notable variations demographically. Certain allergies, such as shrimp, were connected to lower income groups. Non-Hispanic blacks had the most allergies to all allergens with the exception of egg and Russian thistle. Outdoor allergies appeared to have a larger impact on those who lived in urban areas.
"The biggest surprise is that the level of sensitivities didn't differ region to region," said lead author Dr. Darryl C. Zeldin, a scientific director at the National Institute of Environmental Health Sciences. "This goes completely against what most people would have said. The bottom line is that sensitization patterns differ by region, but overall sensitization rates are high."
Among the adult group, the most common positive tests were for grass, ragweed and dust mites, with nearly 20 percent of the population being sensitive to each. Around 12 percent of those over age six were sensitive to cats or dogs. Milk and eggs were the most common positive tests among children. Inhalant allergies such as grass and ragweed peaked among those in their teens and 20s, then decreased later in life.
The study also found that allergies tend to cluster in groups. Those sensitive to dust mites were also likely to be sensitive to grass and tree pollen. Peanut sensitivity tended to cluster with plant allergies, and cockroach and shrimp allergies tended to go together, most likely because they contain a similar allergen, a protein called tropomyosin.
Ganesa Wegienka, an epidemiologist at Henry Ford Hospital in Detroit who was not involved in the research, said the paper provided "a nice snapshot of what's going on in the U.S." She was particularly impressed with the information on clusters.
"This has implications for doctors and patients," she said. "If a child is sensitized to one allergen in a cluster of allergens, maybe the doctor should be looking at other allergens in the cluster to think about treatment plans."