50 million Americans who suffer from allergies or asthma know when fall arrives better than most. If you count yourself in that 50 million and you don’t already own a high-efficiency air purifier such as theIQAir HealthPro Plus, now is a good time to get one. And if you live in Knoxville, Tenn., or a city like it, this is especially good advice. That’s because Knoxville is rated the #1 Fall Allergy Capital by the Asthma and Allergy Foundation of America. The new rankings were released yesterday.

The majority of those millions of allergy and asthma sufferers tend to head indoors when autumn comes. They move inside to avoid the pollen and other triggers of their fall allergies. The irony, of course, is that the outside air becomes inside air every time a door or window opens. And the inside air has additional allergy triggers all its own. In fact, indoor air without an effective air purifier can be worse than outdoor air, a fact not lost on Dr. Clifford W.Bassett, medical director of Allergy and Asthma Care of New York. “Everyone, especially those with allergies and asthma, need to pay close attention to indoor air quality,” Bassett says.

Additional allergy triggers inside the home that will add to the fall woes of allergy and asthma sufferers include mold, dust mites, pet dander, volatile organic compounds in household chemicals and even wood, flooring and paint. An air purifier will make a big difference, but most HEPA air purifiers stop only particles in the air, not gases. Effective gas filtration, such as that provided by the IQAir HealthPro Plus, requires a substantial media such as activated carbon to filter chemicals and volatile organic compounds.

The Asthma and Allergy Foundation of America also recommends reducing household chemical compounds that trigger allergies. “A good step to improving the air quality of your home is as simple as not contaminating it in the first place,” says Mike Tringale of the Foundation. For example, Tringale recommends painting indoor walls with new paints that contain no volatile organic compounds. The Foundation also recommends using portable air purifiers in bedrooms and other common areas at home.

Other advice: Control dust mites by washing linens at least weekly in water hotter than 130 degrees. This will kill dust mites and their eggs. Also, use a high-quality vacuum with no leaks and with a HEPA filter.

Meanwhile, if you live in most areas of the United States you’re not much better off than the residents of Knoxville when it comes to fall allergies. The other Top 5 cities are scattered across the nation, and include Dayton, Ohio, McAllen, Texas, Jackson, Miss., and Oklahoma City, Okla. The rankings are based on the amount of airborne grass, tree and weed pollen and mold spores, allergy medication usage and number of allergy specialists per patient. With a high-efficiency air purifier at home, at least indoors will be free from pollens and other asthma and allergy triggers. And that may reduce or in some cases even eliminate the need for medications and allergy specialists.