Many people don't think of pollen as having an impact indoors. But "if you're outdoors during nice weather, you can bring it in on your clothes or shoes," Fisher says. Pets can bring pollen into the home, too, leading some people to assume they're allergic to their pets when in fact they're actually allergic to ragweed or another type of pollen. To combat this problem, consider wiping pets down when they return from outdoors, keep windows closed in the home and run air conditioning during warmer weather, and change clothes and shoes immediately after returning from outdoors. Also, an air purifier with a HEPA filter can clean the air and keep about 80 percent of pollen out of the home, Fisher says.