NEW YORK (CBS 2) — New research shows indoor allergies could make outdoor allergies even more severe — especially toward the end of summer — when pollen-filled ragweed thrives across the country, CBS 2’s Dr. Holly Phillips reports.

Michelle Jason says she suffers year-round from allergies.

“I’m allergic to a lot of things, almost everything,” Jason said, “indoor, outdoor, mold,dust, everything outside, grass, trees, wool, milk.”

And as a realtor, she knows immediately if there is a cat in the house.

“If I’m hosting an open house, I’ll put the cat in the bathroom and shut the door,” Jason said.

Dr. Cliff Bassett of the American College of Allergy, Asthma and Immunology tells Phillips that people who had year-round or perennial allergies to indoor allergens, “had more sudden symptoms” when ragweed season hit.

Researchers found people with year round allergies have an immune system that is hyper-sensitive from always dealing with their symptoms. So when ragweed season comes along,  their primed immune system overreacts, Phillips reports.

Ragweed, which refers to 15 different types of plants in the sunflower family, grows everywhere in August and September. That’s when doctors say patients who don’t treat their allergies year round will suffer the most.

“Those are the patients that seem to be much more symptomatic during the allergy season and even medications don’t work as well on these individuals,” Bassett said.

Jason says she gets an allergy shot every other week — prevention that can keep her from sneezing and sniffling later.

“You do what you have to do,” Jason said, “you take medication and carry on.”

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