The best air purifiers are a great way to help improve the air space around you and your family. As well as protecting those with health issues from the multitude of air pollutants that gather indoors, those without specific concerns will have peace of mind that the right air purifier will make their environment cleaner. 

The air purifiers that are most likely to give you the most benefit, for example those including a HEPA filter, tend to be at the higher end of budgets — generally into the hundreds of dollars. The size of the unit will also play a huge part in the cost — with the larger units that cover a larger area being greater in price. 

If you have health concerns, or a recurring allergy, keeping pollutants out of your home with an air purifier is definitely worthwhile. Americans now spend roughly 90% of their time indoors, according to the Environmental Protection Agency. It's here that potentially harmful air is able to build up, meaning there are up to five times higher levels of pollutants indoors, than outdoors. An air purifier can help reduce these levels significantly, though not entirely eradicate them, helping you and those around you breathe easier. 

Depending on the type of allergy, and the trigger, air purifiers have also been found to help reduce the presence of particles in the air that cause allergic reactions, which can in turn cause asthma attacks. Dehumidifiers have also been shown to be helpful for asthma sufferers, during times of high humidity. In cases where your indoor space has little or poor ventilation, air purifiers can also come in useful, especially if you are looking to tackle smoke and the resulting odor. 

It is still unclear whether air purifiers do anything to prevent the spread of COVID-19 indoors. The Center for Disease Control (CDC) advises that you should open doors and windows to keep a good flow of air moving indoors — weather permitting, of course. HEPA filters, found in some air purifiers, have been found to remove some viruses from the air. 

“Portable air cleaners, also known as air purifiers or air sanitizers, are designed to filter the air in a single room or area, and they have the potential to improve the indoor air quality in that space,” said Ernesta Jones, from the Environmental Protection Agency.

Jones added that HEPA filters can be particularly useful for those suffering from allergies or asthma. “Multiple studies with portable air cleaners that use a HEPA filter have found improvements in one or more allergy and/or asthma symptoms,” she said. 

“Several studies suggest that using a portable air cleaner where people are spending time, such as in the bedroom while sleeping, may be more effective than leaving it in a central location, such as in the living room.” 

Dr. Deborah Lee, MD and representative for Dr. Fox Online Pharmacy adds that the scientific evidence of research into childhood asthma also indicate that the best air purifiers can significantly help reduce potentially triggering particulate matter within the home. 

"In one study, air purifiers were installed in eight houses, with children with childhood asthma. A control group was also studied which did not have an air purifier," she explains. "After 12 weeks, the treatment group showed a clinical improvement in asthma, with better night-time peak flows, whereas these had deteriorated in the control group. The concentration of particulate matter found in the treatment group had decreased by 43%, and this was significantly greater than the control group."  

Air purifiers require specific conditions to do their best work. How you position your air purifier can make a big difference to the air quality in your home or workplace. So where is the best place to put one? 

"There is no one-size-fits-all answer to this question," Ian Palmer-Smith, gas safety and appliance care expert at Domestic & General, an appliance repair service in the U.K., told Live Science. There are several factors to consider, including the size of the room or rooms, the specifications of the air purifier and the type of air pollution that you intend to reduce. However, there are certain areas in a room that are generally seen as better than others for an air purifier, he said. 

Ideally, several air purifiers should be placed strategically around the house or workplace, with at least one appliance in each frequently visited room. However, if you have just one air purifier, it is better to pick a spot that enables the appliance to catch as many contaminants as possible before they have a chance to spread., "An air purifier should always be in the area which is most polluted," Palmer-Smith noted. This could be the kitchen, pet living spaces or areas close to windows and air vents. 

Air purifiers work by drawing the air through filters and trapping the airborne pollutants, but this approach comes with drawbacks. The fans used to suck up the air can’t be too powerful, otherwise they would create excessive noise and a strong air flow able to blow things off the shelves. As such, air purifiers rely on the environment around them. 

The appliance should be placed in an area with no obstructions and sufficient flow of air, at least 6 inches (15 centimeters) away from any furniture or walls, Palmer-Smith said. This usually means areas near the windows and doorways, or in the middle of the room. Corners and areas cluttered with furniture tend to have the worst airflow. No matter where you put your air purifier, nothing should obstruct its air vents. 

Palmer-Smith noted that air purifiers often work more effectively when not placed on the floor. "As a general rule of thumb, you should place the air purifier 5 or 6 feet [1.5 to 1.8 meters] above the floor to ensure the correct airflow all around the purifier for optimum performance. Putting it on the floor would restrict the airflow and reduce performance." Palmer-Smith said.

Finally, beware of excessive heat and humidity. Placing an air purifier close to the stove or fireplace, in a damp bathroom or near a humidifier can cause damage to the filters and reduce the purifier's lifespan. That is because air purifier filters are typically composed of fine fibers (made out of plastic or activated carbon, for example) that are bound closely together to stop any tiny air particles from getting through, and prolonged exposure to heat or moisture can easily damage these intricate structures.

The best air purifiers say they can help with fine particles in the air, claiming to remove up to 99.9% of particles such as dust, pet dander and other pollutants to improve your indoor air quality. They do this by trapping the particles in a High-Efficiency Particulate Air (HEPA) filter within the air purifier and releasing the cleaned air back into your home. 

While there’s plenty of evidence that air purifiers can help improve air quality, whether they can catch all the dust particles in your home is another matter. According to the EPA, air filters are effective at trapping larger airborne particles like dust, pollen, allergens from dust mites and cockroaches, some types of mold, and pet dander. Yet, these particles tend to settle swiftly, making it challenging for air filters to eliminate them entirely from indoor spaces. 

However, there is good news for people with allergic asthma, often caused by dust mites. Studies show that air purifiers can help people with allergic asthma by reducing dust mites in the home. For example, a 2021 study published in the Allergol Immunopathol journal has researchers collect dust samples from the bedrooms of children with allergies before and after using a HEPA air purifier. They found that concentrations of dust mites ‘significantly’ decreased in the samples after employing an air purifier.

Another 2020 randomized controlled trial found that air purifiers could reduce particles sized 2.5 microns in the homes of children with asthma, reducing the severity of their symptoms and the amount of medication they had to take to control their condition. 

To learn more, Live Science spoke to Dr. Kara Wada, an allergy specialist at The Ohio State University Wexner Medical Center. “Air purifiers are typically most helpful for those with sensitive airways - including those with allergies, asthma and COPD,” said Dr. Wada. “Given that we spend over 90% of our time indoors, ensuring good indoor air quality is important. Air purifiers are most helpful for those with indoor pets and also may be helpful for those with dust allergies. Indoor pet allergens are lighter and more buoyant and stay airborne longer than dust particles which settle more quickly.”

Dr. Wada also advises ensuring your air purifier continues to work at its best by remembering to clean and change the HEPA and activated carbon filters as the manufacturer recommends. “It is important to consider the frequency that filters need to be cleaned or replaced for people with allergies.”

If you want to eliminate tiny dust particles in your home, the EPA suggests choosing an air purifier with a high CADR (Clean Air Delivery Rate) for tobacco smoke – since that includes the smallest particles. Ensure the CADR matches the room or space size where you plan to use it.

In the meantime, discover other ways to remove dust mites from your home with our expert advice. 

10 inch CTO GAC UDF Activated Active Carbon Block Filter for water purifier

Mold is a type of fungi that requires moisture to grow, which is why it thrives in humid areas like bathrooms and basements. As such, investing in a dehumidifier is an effective way to prevent mold growth, because it targets the problem at source. However, an air purifier may still come in handy. Mold reproduces by releasing spores, which are tiny airborne "seeds" invisible to the naked eye. Like pollen, they travel by air, searching for fertile grounds. "Air purifiers can certainly help in removing the mold spores and therefore prevent them from spreading," Ian Palmer-Smith said. 

However, mold spores vary in size, with some species measuring just 2 microns (approximately 0.00008 inch), according to the U.S. Environmental Protection Agency. To efficiently capture them, an air purifier should be equipped with a membrane designed to remove particles as small as 0.3 microns, known as a high-efficiency particulate air (HEPA) filter. "The better the HEPA filter is, the more effective it will be in removing these particles," Palmer-Smith said. Some appliances also have a pre-filter that will trap some of the largest mold spores before they reach the HEPA filter. 

Still, no matter how advanced the air purifier is, it will not be able to remove the underlying causes of the mold or get rid of the existing infestation.

The best air purifiers claim to banish bad smells and enhance indoor air quality, but the final verdict on their effectiveness remains unclear.

According to the US Environmental Protection Agency (EPA), air purifiers can help make indoor air cleaner and fresher by reducing pollutants. However, they emphasize that not all odors are guaranteed to disappear. The EPA's 2018 Consumer Guide to Air Cleaners in the Home suggests using air purifiers as a little extra help and proper ventilation to keep the air smelling better and improve overall air quality. So while they might not magically make your home smell like roses, they can make a positive difference, especially if you spend a lot of time indoors.

But when it comes to solid evidence, specifically about air purifiers banishing odors, the research isn't all there. Most studies focus on improving air quality and health rather than tackling smells head-on. For instance, a 2021 systematic review in the Science of The Total Environment Journal looked at more than 20 studies in different settings and found that air purifiers could cut indoor air pollution by up to 92%. A 2020 in the International Journal of Environmental Research and Public Health showed some improvement in regular homes, though not enough to be statistically significant.

So how do these air purifiers work? They filter and trap particles that contribute to bad smells. However, the EPA warns that no filter can catch every odor-causing particle. Also, the size of the room matters. To freshen up a large space, you'll need a bigger air purifier with a higher Clean Air Delivery Rate (CADR) to get the job done.

The ability of air purifiers to tackle specific odors depends on their design. Some models can handle moldy smells, cooking aromas, pet odors, and cigarette smoke. There are even air purifiers equipped with activated carbon filters that can take on gas and chemical odors emitted by household cleaners. But these filters have their limits and can only handle a specific set of gas pollutants. They can't touch carbon monoxide, a dangerous gas emitted by wood-burning stoves and gas fires.

It’s also worth pointing out that quality can vary between brands, and to keep your air purifier working at its best, you’ll need to replace the HEPA filter and activated carbon filter as often as the manufacturer recommends.

So, while air purifiers have the potential to improve air quality and reduce indoor pollution, we're still waiting for solid proof that they're the ultimate odor busters. They might help but don't expect them to zap away all bad smells magically. If you're considering buying an air purifier, it's a good idea to do your research first and understand how different models work before banking on them to keep your place smelling fresh.

You’ll notice most of the air purifiers for rooms that we tested have something called a high-efficiency particulate absorbing (HEPA) filter. These can remove 99.97 percent of air pollutants from 0.3 microns in size, which basically means they are really effective at getting rid of the majority of indoor air pollutants.

For context, most dust particles are about five microns in size, and pollen is a staggering 10-1,00 microns – all of which a HEPA filter is able to trap and remove.

Perry tells Live Science that while the most effective air cleaners can remove lots of different types of particles, you’ll never get 100 percent pure air.

He says: "The idea of an air purifier is that it’s designed to get rid of the impurities in your home and neutralize any nasties, such as dust, smells, pet dander, smoke, bacteria and viruses.

“Air purifiers work by having a fan that sucks the dirty air in the home into filters. These then remove any impurities before releasing the cleaned air back into the room. It's important to note, however, that it’s impossible to get rid of all particles, which can live on walls, carpets, bedding and hard surfaces.”

For many of us, clean air can make our living space more comfortable. But for those who struggle with respiratory problems, such as allergies, asthma or COPD, the presence of harmful airborne particles can make their symptoms unbearable and directly endanger their health. Similarly, immunocompromised individuals may feel much safer knowing that their air purifier will trap microbes that can make them very sick. 

As Perry points out, we may still need more large-scale studies to assess the exact effect of air purifiers on our health, but it’s hard to deny the fact that, for some, these devices may be indispensable. 

“It makes sense that the cleaner the air, the easier it is for anyone with breathing problems and susceptible to allergies,” he says. “If you’re an asthma sufferer and want to purchase an at-home air purifier, then it’s a good idea to keep a diary to see if it does make a difference in symptoms. Remember though that an air purifier will not get rid of all impurities so asthma needs to be managed as prescribed by your doctor.”

“The same goes for people who suffer from allergies, the cleaner the air and being able to manage pollen and dust is going to help and will be dependent, of course, on the time of year when pollen count is higher.”