Air purifiers can significantly improve the quality of life around the home, but those suffering from allergies and other respiratory issues may need extra assurances. Here are answers to some of the most common questions when it comes to allergies and air purifiers.

Air purifiers do work for reducing the amount of pollen in the air, which should in turn alleviate allergy symptoms. However, results will differ from person to person. Exactly how well an air purifier works will vary based on the size of the room where it’s located, the local weather, the purifier model, and your own personal health. Honeywell actually got into legal hot water for overstating the effectiveness of its air purifiers, so be wary of bold claims by manufacturers.

For best results, ensure the air purifier you have is in the room where you spend the most time, that it has a proper HEPA filter installed, and that it’s running all day. Pollen will seep in through your windows over time, or settle onto the carpet to be released later. An air purifier won’t work if you leave it running for a few hours, then turn it off.

Air purifiers don’t work alone, either. As a primary defense against allergies, you’ll want to close windows in the house and change clothes when you get in from the outdoors.

Only ionizing air purifiers are likely to exacerbate allergies (more on them later). Studies have shown that air purifiers can help those with common allergies by catching pollen and other irritants within their filters, but there is still little wide consensus on the issue.

Besides mitigating the effects of allergies, air filters can remove odors from the air and help you sleep better. Effectiveness will range depending on the type of filter you’re using. For example, activated carbon filters will be better for removing odors, but not as good at removing pollen from the air. Higher-end air purifiers will include multiple types of filters to cover all the bases.

The one instance where an air purifier would do more harm than good is if it uses ionization. Ionizing air purifiers draw pollen to its filters via electrification. One side effect of this is bonding oxygen atoms and creating ozone. Even in small quantities, ozone can irritate the lungs and make your respiratory issues worse.

Air purifiers also need power to run and produce some background noise. You’ll also need to replace the filters occasionally, but those are more maintenance chores than side effects.

Air purifiers are not a foolproof deterrent for COVID-19, but can be part of a wider range of indoor safeguards. COVID-19 is spread via droplets in the air, and air purifiers can catch those droplets provided their filters are rated for particles smaller than 1 micrometer. Proper ventilation is a better form of protection, but an air purifier can help when ventilation is difficult to implement.

Air purifiers can help with respiratory health, and not only when it comes to allergies. Just be sure to get one that uses a proper HEPA filter and avoid any that produce ozone.