The study included 123 people allergic to ragweed

"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," said 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."

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), and 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," said 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."