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Man’s Best Friend? Not During Hay Fever Season

Study Suggests Allergy to Dogs (and Cats and Dust Mites) Worsens Ragweed’s Impact

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Ragweed allergy season can be even worse for those with dog, cat, or dust mite allergies, according to new research. These year-round allergies appear to “pre-prime” the immune system so symptoms hit harder, according to a study published in the Annals of Allergy, Asthma & Immunology, the scientific journal of the American College of Allergy, Asthma and Immunology.

Hay fever (known as seasonal allergic rhinitis) begins around the middle of August, when ragweed blooms. The typical symptoms – sneezing, itching, stuffy nose, and watery eyes – can make people especially uncomfortable. People with hay fever who also are allergic to cats, dogs, or dust mites develop symptoms faster and (early on) more severely, the research suggests. Treating the cat, dog, or dust mite allergy year round may help make the hay fever more manageable.

“People with hay fever react differently when ragweed allergy season arrives. Some start sneezing right away, and others don’t, so we wanted to determine what makes certain people develop symptoms more quickly,” says allergist Anne K. Ellis, MD, lead author of the study and an ACAAI member. “We tested a number of common perennial allergens and found that having an allergy to cats, dogs, or dust mites sets hay fever sufferers up for faster onset of symptoms when exposed to ragweed.”

Those who tested positive for cat, dog, or dust mite allergies developed symptoms either faster than or to a greater degree than those who tested negative for those allergies.

The study included 123 people allergic to ragweed. Of those, 66 percent tested positive for cat allergies, 63 percent tested positive for dog allergies, and 73 percent tested positive for dust mite allergies. All were exposed to ragweed for three hours in a special controlled room called the Environmental Exposure Unit (at Kingston General Hospital, Ontario), where they completed symptom questionnaires every 30 minutes during exposure.

“On average, those who tested positive for cat, dog, or dust mite allergies developed symptoms either faster than or to a greater degree than those who tested negative for those allergies,” says Dr. Ellis. “The differences seen at 90 minutes of exposure were less dramatic after 3 hours of exposure, however. That suggests that once the hay fever season is in full swing, the symptom differences between those with cat, dog, or dust mite allergies and those without no longer exist.”

To avoid the more intense early reaction, people with cat, dog, and dust mite allergies should try to limit their exposure to those allergens before ragweed season starts, according to Dr. Ellis. Because that often is not practical when it comes to family pets, an alternative is to treat their cat, dog, or dust mite allergies, she adds.

“Allergy immunizations or year-round allergy medication can provide hay fever relief to those sufferers who have ongoing symptoms from cats, dogs, or dust mites, even if they think the symptoms are mild and easily tolerated,” says Neil Kao, MD, chair of the ACAAI’s Rhinitis/ Sinusitis Committee. “They’ll likely find ragweed allergy season easier to endure if they’re treating their perennial allergies.”


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This article was originally published in Coping® with Allergies & Asthma magazine, September/October 2010.