According to the Environmental Protection Agency, the best way to improve indoor air quality is to get rid of the source of pollutants and ventilate your interior spaces with clean outdoor air. While air purifiers can reduce airborne pollutants, they cannot eliminate them. They also can’t clear the dust, dander and other particles that have already settled on surfaces around your home.

But that doesn’t mean air purifiers aren’t effective in the real world. In fact, the best air purifiers are really good at filtering out fine particles like smoke, dust, pet dander and pollen. Anecdotal evidence suggests that users feel better when they run these devices in their homes — even if the long-term health benefits aren’t well-studied.

Here are five situations in which an air purifier could probably help you out:

You have respiratory issues, allergies, or asthma

Allergy sufferers and people with asthma or other breathing problems may notice some reduction in symptoms, like wheezing and coughing, when using an air purifier with a HEPA (high-efficiency particulate air) filter designed to catch 99.7% of particles larger than 0.3 micrometers. (Don’t settle for devices that promise “HEPA-like” or “HEPA-style” filters.) The Trane CleanEffects® Whole Home Air Cleaner captures particles as small as 0.2 micrometers.

Some of these devices do a decent job of catching common irritants, including pollen, pet dander and dust, so unless your purifier’s fan simply stirs up pollutants, it likely won’t make your issues worse. Research suggests that devices with HEPA filters “appear to be” beneficial as long as they’re maintained regularly.

You have pets

There’s no such thing as a truly hypoallergenic pet. Even dogs that don’t shed will release skin and dander into the air — and animals collect pollen and dust in their coats. You may not be allergic to your pets specifically, but that doesn’t mean their fur won’t cause problems.

High-quality air purifiers worth purchasing come with pre-filters that catch the big stuff, like pet hair, before it even gets to the main HEPA filter. Machines with carbon or charcoal filters that trap odor compounds may also be able to reduce pet smells.

Be sure to clean your home (and bathe your pet) regularly. Filtration can help minimize the effects of pet dander, but it can’t eliminate them entirely.

You smoke — or you live with a smoker

Cigarette smoke (including secondhand smoke) has significant negative effects on your health and the health of those you live with. In fact, any amount of secondhand smoke poses a risk. Simply opening a window does not protect against these problems, but ventilation and filtration, such as with a HEPA filter that catches fine particulate matter (PM 2.5, or 2.5 micrometers), can provide some relief.

Tobacco smoke is one of the three particles included in an air purifier’s clean-air delivery rate (CADR), which is measured in cubic feet per minute. So a CADR of 80 for dust would mean that 80 cubic feet would be cleaned of dust every minute. Smoke has the smallest particles of the three categories (compared to dust and pollen), so choose a device that rates highly in this area if tobacco smoke is a concern.

You live with kids or roommates

You may be the cleanest, tidiest person on earth, but you can’t control how your kids, roommates or guests behave. If other people aren’t as diligent as you are about decluttering, or if they track in dust, dirt, pet hair and pollen from outside the home, an air purifier can help carry the burden of filtering and clearing those pollutants.

You live on a busy street or around construction

Air purifiers can catch some of the airborne particles, like dust, that get kicked up during construction or from cars driving down the road. Keeping your windows closed may keep some of the debris at bay, but an air purifier can filter what gets through the cracks. Running one of these devices could help you breathe a little better.