Buying an Air Purifier for Asthma

asthma air purifier

Air is a gas. It’s made up of about 80% nitrogen molecules and 20% oxygen molecules.

Breathing in air can trigger an asthma attack in three different ways:

  • The air itself, under certain conditions (such as when it’s really cold), can trigger an asthma attack.
  • Air can easily mix with other gases – these “other” gases can trigger an asthma attack.
  • Air can also “contain” different particles (solids and liquids) – these particles can trigger an asthma attack.

Asthma Triggers For Which An Air Purifier Can’t Help

An air purifier removes unwanted gases and particles from the air. It will not heat or cool the air, so if your asthma is triggered by cold air an air purifier will not help. It will also not help if your asthma is triggered by

  • Acid Reflux
  • Exercise
  • Emotional Stress
  • Medications – e.g. aspirin
  • Hyperventilation, laughing, crying

The above really goes without saying but the point here is that an air purifier is by no means a cure-all for every type of asthma. Consult with your doctor if your asthma is triggered by any of the symptoms listed above.

Note: We also advise you to consult with a doctor before buying an air purifier for any of the asthma triggers we list below. There’s simply no replacement for professional medical advice although we will do our best in the guide that follows below.

Asthma Triggers For Which An Air Purifier Can Help

1. Allergens

Including dust mites, molds, airborne cockroach feces, pet dander

Allergens are the most common asthma trigger (about two thirds of Americans have allergic asthma). Allergic asthma is so common that it takes up a whole category of asthma: All asthma can be categorized as

  • allergic asthma
  • non-allergic asthma

Allergic asthma is, of course, caused by inhaling allergens. For you to inhale them they must be airborne. And for them to be airborne, they must become airborne and stay airborne.

For this to happen they need to be quite small. Furthermore, for them to make their way all the way down to your lower airways to trigger asthma, they have to be even smaller.

The cut off is 10 microns. Particles larger than 10 microns won’t make it past the top of your voice box (larynx). Particles smaller than 10 microns have the ability to make their way all the way down your windpipe and into your lower airways where they can do the most damage as it relates to asthma attacks*.

Thus, an allergen that’s a good candidate for an asthma attack is going to be on the smaller side of the particle size spectrum.

Common allergens that can be a problem for asthma sufferers include

Here’s the good news. No matter what the allergen and no matter what its size, the filter we recommend to remove that allergen from the air is the same.

What we’re talking about is a HEPA filter. HEPA filters are extremely efficient capturing even the smallest particles . That means that they will efficiently remove the exact particles - particles smaller than 10 microns  - that can trigger asthma attacks.

Even more good news: most air purifiers on the market are equipped with a HEPA filter.

Once you’ve narrowed down your choices of air purifiers to only those that are equipped with HEPA filters the next step is to choose a model that will process air at a high enough rate to

  • be able to process all of the air in the room
  • be able to keep up with new allergens entering the room

Our testing has showed that 250 CFM units offer the best combination of value, energy efficiency, and low noise output for rooms all the way up to 300 sq. ft.

Here’s the thing though: If your asthma is indeed triggered by allergens this is a serious issue. More so than someone simply buying an air purifier to reduce airborne dust in their home, for example.

For this reason, we are inclined to be much more conservative in our estimate for those consumers looking to buy an air purifier for asthma:

Our recommendation is therefore one 250 CFM unit per 150 sq. ft. for consumers buying an air purifier for asthma.

This effectively doubles the rate at which the air purifier is able to process all the air in the room. It also allows the air purifier to much better keep up with new allergens entering the room.

Remember, air is a gas and gases mix very easily. Even if you keep the room completely sealed all it takes is opening the door for a moment for allergens from outdoor air or even air in an adjacent room to flood into the room.

The two best rated 250 CFM units we’ve tested so far are the following

For larger spaces

If you need to purchase an air purifier for a space larger than 150 sq. ft. we would recommend simply purchasing more 250 CFM units.

Not only will this allow for better, quicker distribution of clean air (with multiple units) but it is also a much better value than purchasing a single high CFM unit. You can essentially purchase two 250 CFM units (which equates to 500 CFM) for about the same price and many times less than a single high CFM unit in the 350 to 400 CFM range. Single units with a CFM greater than 400 CFM are, for the most part, exorbitantly priced and nowhere close to being an option for the average consumer.

*Some studies have shown a link between allergic rhinitis (hay fever) and asthma. Thus, particles large enough to trigger an allergic response in the upper airways (10+ microns) very well may also trigger asthmatic symptoms in the lower airways. The good news? A HEPA filter will do just as well filtering larger particles as it does smaller particles.

2. Pollution

Outdoor air pollution becomes indoor air pollution the moment you open a window or door. And, once it’s indoors, it’s something you can take care of with an air purifier.

As we talked about earlier, asthma is a condition that primarily affects the lower airways and so we want to prioritize particles that can reach this area of your body. That means prioritizing particles smaller than 10 μm.

However, as we also discussed earlier, there’s no need for you to worry about this – which size particles you need to prioritize and which type of filter to get for those particles - in your search for an air purifier.

A HEPA equipped air purifier will take care of particle pollution, no matter the size of the particles. The same recommendations we made earlier apply here as well.


1. Studies have shown there to be a direct correlation between increased particle pollution (PM) and an increase in asthmatic attacks. So, even if you do not believe that air pollution is a trigger for you, consider carefully that it may very well be and that you just may not be aware of it.

2. The EPA has classified particles smaller than 10 μm as “particles of concern even for nonasthmatics. Again, particles this size can make their way all the way down to your lower airways. When they reach this far inside your body they can certainly trigger an asthma attack, but, depending on the concentration and composition of the particles, can be hazardous to nonasthmatics just the same. So, if particle pollution concentration is high in your area, even if you’re nonasthmatic, an air purifier is recommended.

3. Upper respiratory infections – e.g. colds

An air purifier won’t cure the common cold but, consider for a moment what causes the common cold – a virus. As we discuss at length here, viruses, as it relates to air purification, are nothing more than airborne particles. Viruses are extremely small particles but not small enough to make it through a HEPA filter.

Thus, you can reduce the risk of getting the common cold, at least inside your home, using an air purifier.

Again, a HEPA equipped unit will get the job done. Our recommendations from earlier.

4. Secondhand smoke

Secondhand smoke is another common trigger for asthma attacks. We address buying an air purifier for smoke here.

The main takeaway from our research is, you guessed it– a HEPA filter is good enough to remove smoke particles from the air.

The gaseous components of smoke are a bit more tricky. Fortunately, gaseous components are just that – gases. So you’re able to remove them from a room much more readily than particles. You can simply open a window or turn on a fan – ventilate – to remove most gaseous components from the air in a room.  

You can also use an air purifier. Here, however, is where a HEPA filter falls short. HEPA filters can only remove particles – solids (and liquids) – from the air. They cannot remove gases. To remove gases you need a material that can bond to the gas to remove it from the air. The filtering mechanics employed in a HEPA filter won’t work.

The most common material used for this application is carbon. That’s why most air purifiers on the market are equipped with a carbon filter – for gas filtration – in addition to a HEPA filter - because the HEPA filter can only take care of particle filtration.

It’s important to realize that not all carbon filters are created equally. The best type of carbon filter is pellet-based.

Remember, carbon removes gases from the air by physically bonding to them. The greater the surface area of the carbon, the more chances there are of that bonding taking place as these unwanted gases (mixed in with air) are passing through the air purifier. Pellet based carbon filters have a much greater surface area – for bonding to take place – than fibrous filters that are simply coated with carbon. This makes them much more effective for filtering gases – such as the gases that make up secondhand smoke.

Only one of the top rated air purifiers we recommend feature this type of filter – the Winix 5500-2. Its pellet based carbon filter (in addition to its HEPA filter) make it the clear choice if you’re looking for an air purifier for second hand smoke. 

5. Strong Odors and other chemicals (like NO2)

To remove other gases like strong odors and gaseous chemicals like NO2 you once again have two options

  • ventilate
  • trap the chemical with a carbon (or similar) filter

Again, we recommend a unit with a pellet based carbon filter. The Winix 5500-2 is the only reasonably priced option on the market.

So, what is the best air purifier for asthma?

For triggers that consist of mostly particles – including allergens, particle pollution, and viruses that cause colds

a HEPA equipped air purifier will work just fine.

For triggers that include gaseous components – including smoke, odors, and other chemicals

a unit equipped with a pellet-based carbon filter is recommended.

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