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If you have allergies, asthma, or another respiratory condition, you’ve probably wondered whether an air purifier could help. The concept is tempting: in theory, these machines filter out pollutants, particulates, and other impurities, leaving you with fresh, clean air in your home. But do air purifiers really work — and can they benefit your health? Here’s what you need to know about these popular devices.

The Ins and Outs of Air Purifiers

To understand what air purifiers can and can’t filter, it helps to understand what could be in your air. In general, indoor air can contain two main types of pollutants: particulate matter and gaseous pollutants. Particulate matter is any kind of microscopic particle found in the air, such as pollen, dust, dust mites, animal dander, and mold. As their name suggests, gaseous pollutants are gases produced by paint, new carpet, cleaning products, and wood or gas stoves. Some indoor air pollutants contain a mix of both these types. Most home-based air purifiers can only remove particulate matter and sometimes a small amount of gaseous pollutants.

There are also two main mechanisms for cleaning indoor air. They are available as either units that clean the air for one room, or as central filtration systems that must be professionally installed.

Mechanical air filters

These machines use a filter to trap larger particulate matter, such as dust and allergens. They may not be as effective at filtering smaller particles, bacteria, or viruses, however. Mechanical air filters include high-efficiency particulate air (HEPA) filters.

Electronic air filters

This category of air purifiers includes electrostatic precipitators and ionizers. They charge the particles so they can be trapped on surfaces. However, electronic air filters can also produce ozone, which can irritate the lungs and exacerbate existing respiratory conditions, negating any beneficial effects.

Can Air Purifiers Help Your Health?

Evidence to support the alleged health benefits of air purifiers is mixed. For example, some research suggests that these machines may help decrease levels of airborne allergens, such as pet dander and dust, in a home. While some studies have found mild improvement of symptoms in people with allergies or asthma who use air purifiers, the machines aren’t a first-line treatment for these conditions. Instead, you’re better off preventing indoor air pollution in the first place by keeping your home clean and free of allergens and other particulate matter.

If you think a HEPA filter or other type of air purifier might benefit you, be sure to do your research before making a purchase. Check rankings and reviews of air purifiers, such as those available from Consumer Reports. Your physician can give you more suggestions for managing allergies or asthma effectively.