5 Ways Americans’ Allergies Are Getting Worse

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Allergies are going nowhere but up. One in five Americans now suffer from allergies, accounting for 17 million doctors appointments and 30,000 emergency room visits each year. And the numbers are on the rise, according to a large new study from the medical testing and information company Quest Diagnostics.

Plumbing the largest data set of its kind — including more than 2 million patient visits for allergies over four years — Quest analyzed the results of blood tests to 11 common allergens: five foods (egg whites, milk, peanuts, soybeans and wheat), common ragweed, mold, two species of house dust mites, cat epithelia (skin), and dog dander.

(More on TIME.com: Q&A: Is This Year Really the Worst Allergy Season Ever?)

Here’s a rundown of the study’s main findings:

1. Ragweed and mold allergies are up — blame climate change

Over four years of testing, the Quest researchers found, the rate of allergies increased across the board — but most significantly to ragweed and mold. Overall allergy rates increased nearly 6%, but allergies to ragweed shot up 15% over the same time period and those to mold increased 12%.

The culprit: climate change. As the planet warms, ragweed and mold are better able to thrive. Indeed, a recent study associated warming with a longer ragweed pollen season (because spring is arriving earlier, causing flowers and pollen to bloom sooner), especially the farther north you go. In some northern areas of the U.S., namely Minnesota and Wisconsin, the study found, the allergy season is now about two weeks longer than it was in 1995; if you go farther north into Canada, it’s up to a month longer. The Quest study found the highest rates of ragweed allergy in the Great Lakes states, the Southwest, mountain states and the Plains.

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Warmer temperatures also mean more mold and more mold allergies, which is particularly troubling because mold exacerbates asthma and may trigger allergic sensitivities.

2. Kids are more allergic than adults, especially to peanuts

Children are about twice as likely to have severe allergy symptoms than adults. Of kids age 2 to 17 who were blood-tested for allergies, 53% showed sensitivity to at least one allergen. Among those children, one in five showed a high degree of sensitivity, compared with one in 10 adults.

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Peanuts were the most common food allergy in kids aged 6 to 18, affecting nearly a quarter of all school-aged children tested. Peanut allergy was even more common in children age 5 or younger, affecting about 30% of kids in this age group. The Quest study found that peanut allergies increased over the four-year study period — by 2% in kids age 8 or younger and by 1% in those age 9 to 18.

3. Poor kids are less likely to be tested early, which contributes to the “allergy march”

Kids who develop food allergies early in life are more likely to develop more severe allergic disease, including asthma, later on — particularly if they’re not treated early. The Quest data backed up that phenomenon, finding that the highest rates of food allergy occurred in kids and declined with age. Other allergies appeared more frequently with age, with ragweed, dust-mite and pet allergies remaining high through age 40.

The Quest study also looked at rates of early testing in the kids in the study: it found that low-income kids covered by Medicaid were 18% less likely to be tested for allergy before the age of 5, compared with wealthier children with private insurance. At older ages, that pattern reversed; from age 6 to 12, kids covered by Medicaid were about 20% more likely to be tested than kids with private insurance. That suggests that allergy testing in low-income children is delayed, which means they may be missing treatment during the critical early years of life. These children may be more likely to progress along the allergy march, increasing their risk for asthma and other more severe allergies.

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4. Men may be more allergic than women

Previous studies suggest that women have more allergies than men do, but the Quest data showed that men were actually more likely to test positive for allergies at all ages. The authors note: “a meta-analysis of allergy prevalence that reviewed 591 studies found that males made up 64% of people 18 years of age or younger identified with allergies, but women made up 65% of adults identified with allergies after age 18.”

The reason for the discrepancy isn’t clear, but the authors have a few theories: a) it’s possible that girls and women are simply tested for allergies more often than boys and men; b) allergies in men have been underestimated, which means they’ve been potentially undertreated; or c) the criteria for allergic sensitivity may depend on gender and may change with age.

5. Some U.S. cities are more allergic than others

Allergies are bad everywhere, but some big cities have it worse than others. The Quest data showed that four of the five cities where people were most allergic to ragweed and mold were in the Southwest; as for pet, dust-mite and food allergies, there were no regional differences. The study ranked 30 big cities according to allergy rates. The top 10 most allergic cities were:

1. Dallas

2. Phoenix

3. Baltimore

4. Washington, D.C.

5. Boston

6. Philadelphia

7. Chicago

8. Cincinnati

9. Atlanta

10. Cleveland

Get PDFs of the full city ranking and the entire report. Check out Quest’s Allergies Across America site here.

More on Time.com:

Eldest Children Have Allergies More Often than Their Siblings

Get Out the Kleenex — Climate Change Lengthens Allergy Season

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