If you have allergies, asthma, or another respiratory condition, you\u2019ve 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 \u2014 and can they benefit your health? Here\u2019s what you need to know about these popular devices.\nThe Ins and Outs of Air Purifiers\nTo understand what air purifiers can and can\u2019t 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.\nThere 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.\nMechanical air filters\nThese 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.\nElectronic air filters\nThis 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.\nCan Air Purifiers Help Your Health?\nEvidence 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\u2019t a first-line treatment for these conditions. Instead, you\u2019re better off preventing indoor air pollution in the first place by keeping your home clean and free of allergens and other particulate matter.\nIf 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.