The Best Air Purifier for Allergies
A quick look at what causes airborne allergies and which air purifiers are best for allergies.
The allergen problem
An allergy involves a reaction of the body’s immune system to what is usually a harmless substance – a substance that doesn’t have the same effect on most other people.
In a non-allergenic person:
- A particle lands (eg. inside the nose)
- Mucus moves the particle to the throat
- The particle is swallowed or coughed out
In an allergic person:
- A particle lands
- The body releases histamine and other chemicals
- The histamine/chemicals cause certain cells to contract (congestion), itch, make more mucus, etc.
Of course, for an allergic person, this isn’t a pleasant experience.
So, what can you do about it?
- You could treat the effect of the problem – in other words, treat yourself – for example, take medication to improve symptoms
- You could also treat the cause of the problem – remove the allergens themselves
Now think about this:
Allergens cause allergic reactions. In other words, an allergen is absolutely necessary to trigger an allergic reaction.
If you remove the allergen, this prevents the allergic reaction from happening in the first place.
The beautiful thing here is that you can do this at all. There’s plenty of ailments that you cannot prevent. But you can prevent allergies caused by airborne allergens. You can actually get to the root of the problem – the cause of the problem - and fix that, instead of just treating the effect of the problem – the allergic reaction and accompanying symptoms.
Air purifier recommendations
Most allergies are triggered in the upper airways. A particle needs to be 10 μm (micrometers) or larger to get stuck in the upper airways for it to trigger an allergic reaction. This means that you could theoretically get away with only removing particles 10 μm or larger to prevent most allergies.
But, why would you? Some allergies in some people can absolutely manifest in the lower airways (a particle has to be 10 μm or smaller to reach the lower airways). You may be one of those people. But even if you’re not, why wouldn’t you want to filter out these smaller particles as well? Such particles no matter if they’re allergenic or not, in sufficient concentration and particular composition, can certainly cause all manner of health problems in their own right.
Here’s the good news: You don’t even need to make that distinction – make a decision – between removing particles 10 μm and larger or 10 μm and smaller. An air purifier equipped with a HEPA filter takes care of all airborne particles – no matter what their size.
Even more good news: most air purifiers on the market are equipped with a HEPA filter. HEPA filters at worst remove 99.97% of particles from the air. That means that for every 10,000 particles that go through a HEPA filter, only 3 make it through – and that’s a worst case scenario. It can very well filter with up to 100% efficiency.
You just need to make sure that the air purifier you buy has
a HEPA filter
easy to do – just check the product’s description for “HEPA filter”
sufficient air processing power (given as CFM – cubic feet per minute) for all the air you need to purify
a little more difficult to do. We’ll take about this next.
Our testing and research has shown that 250 CFM units have sufficient output for rooms up to 300 sq. ft. If the space is larger, then our advice is to simply buy more 250 CFM units. So, if the space is 400 sq. ft., buy and install two 250 CFM units. 900 sq. ft.? Then three 250 CFM units are recommended.
For spaces smaller than 300 sq. ft. we still recommend a 250 CFM unit. In such smaller spaces all you have to do is run these units on a lower fan speed. At lower fan speeds, top rated 250 CFM units exhibit extremely high energy efficiency and low noise output. Lower CFM units are not much cheaper and are usually much less energy efficient and noisier.
Special recommendation for especially sensitive allergy sufferers
While our normal recommendation of one 250 CFM unit per 300 sq. ft. will work for most allergy sufferers, it may not work for everyone. If you're especially sensitive to airborne allergens we recommend that you purchase one 250 CFM unit per 150 sq. ft.
This effectively doubles the amount of air the unit processes in a particular room per unit time. But, more importantly, it will make the unit much more effective in “attacking” new allergens as soon as they enter the room.
Maximum attack speed
An air purifier intakes “dirty” air (in this case air that contains allergens), forces that air through a filter (in most cases a HEPA filter) and then outputs cleaned particle-free air.
Recall that a HEPA filter only needs to process a particular block of air once to remove the vast majority (if not all) particles from it. Two things make this more or less difficult:
- the amount of “dirty” air that is already in the room
- the amount of “dirty” air that’s constantly coming into the room
Let’s say the room is completely sealed with no incoming or outgoing air. In this case there would be a set amount of “dirty” air in the room and the air purifier would only need to process that set amount of air once to clean it completely.
A 250 CFM air purifier that processes 250 cubic feet of air per minute could be put into a room containing 1,000 cubic feet of air and process all that air in 4 minutes (1000/250 = 4). You could theoretically turn on the air purifier, run it for 4 minutes, and then shut it off with perfectly clean air.
The problem with this hypothetical scenario is that it’s just that – only hypothetical. In real life scenarios a room is rarely completely sealed and furthermore, “dirty” air is constantly added to the room while clean air is leaving it.
“Dirty” air enters when
You run the AC/Heat
if air containing allergens is present in higher concentrations in another part of your home the HVAC system acts to distribute that air every time it’s turned on.
You disturb any surface
remember the dust particles that pet allergens tend to associate with? Those dust particles settle on surfaces but can easily become airborne when you do something as seemingly innocent as walk across a carpet or sit down on a couch
You open a door or window, for even just a few seconds
especially if pollen counts, mold spore counts, etc. – the source of the allergen – is high. “Exposing” the room to air with a high allergen concentration even for a few moments will essentially flood the room with those allergens
Now imagine a room that’s more indicative of a real life scenario. The HVAC system may be running, you and/or your family is constantly moving around in the room, doors are opening and closing, etc.
By limiting yourself to 250 CFM of air processing power per 150 sq. ft. you are enabling the air purifier to “attack” incoming airborne allergens much faster.
In a 300 sq. ft. space with 10 ft. ceilings the total air in the room is 3000 cubic ft. of air. A 250 CFM air purifier can process all the air in such a room once every 12 minutes (3000/250 = 12).
In a space half the size the same air purifier can process all the air in the room once every 6 minutes. So as those allergens are added to the room the air purifier can process them twice as fast.
What about larger spaces?
250 CFM air purifiers provide the best combination of processing power, energy efficiency, noise output, and value.
Higher CFM units do exist but we generally do not recommend them, if for no other reason other than value. For example, you can buy two 250 CFM units which equate to 500 CFM for close to the price of one 350+ CFM unit. It is primarily because of their great value that we recommend multiple 250 CFM units over a single higher CFM unit for larger spaces.
The great thing about this approach is that you can start by purchasing an individual 250 CFM unit at a relatively low price point. You can then experiment with that single unit and only purchase more units if you find results unsatisfactory.
You can determine results in two ways:
If your symptoms are reduced or eliminated
then the air purifier is clearly effective. If not, you need more CFM. And to get more CFM, purchase additional units.
Purchase a particle meter.
A particle meter will tell you the exact concentration of particles in the room. It will show you the initial concentration, the gradual reduction in concentration as the air purifier is running, and the lower threshold of concentration the air purifier is able to achieve. This last bit of information is very important for larger spaces. If you’re an allergy sufferer you want this concentration to be as low as possible. Even 0 if it’s possible.
Conclusion - so, what is the best air purifier for allergies?
Again, 250 CFM air purifiers provide the best combination of processing power, energy efficiency, noise output, and value.
We specifically recommend these models:
To learn more about combating specific allergens:
For those especially interested in combating airborne allergens, the next section of this guide goes further in-depth and takes a more scientific approach to this problem.
A scientific look at particles entering the body
If you have a food allergy you make sure to not eat the food that triggers your food allergy. The same logic applies to airborne allergens. If you have an allergy caused by an airborne particle you make sure to not breathe in the airborne particle.
But what happens if you do breath in a particle? What makes a 10 μm or larger particle deposit in the upper airways? What allows smaller particles to get to lower airways? What happens, in general, when a particle enters the respiratory system? We answer these questions and more below.
Air movement top to bottom through the respiratory tract
1a. Nose - nasal cavity (lined with mucous membrane that filters and traps particles/pollutants)
2. Pharynx (part of throat directly behind mouth and nasal cavity)
3. Part of larynx (voice box) above the vocal cords
4. Part of larynx below the vocal cords
5. Trachea (wind pipe)
6. Right and left bronchi
7. Secondary bronchi
8. Tertiary bronchi
Particles are deposited in the respiratory tract
In one of four ways
the particle moves along its normal path (with the air) but gets so close to the surface of the tract that it touches the surface and is thereby intercepted/deposited
the particle moves along its normal path with the air but at some point goes its own way and makes impact with the surface of the tract and is thereby deposited
gravity and air resistance cause the particle to settle on the surface and it is thereby deposited
the particle is small enough to move randomly onto the surface and it is thereby deposited
These three factors determine how far and by what method a particle is deposited in the lungs:
- particle size
- particle shape
- particle density
Note that only particle size determines how well a particle is filtered by a HEPA filter.
|Particles larger than 10 μm
|Particles 2.5 to 10 μm
|Lower Airways - Deep breathing = Bronchioles and alveoli, Shallow Breathing = Trachea and large bronchi
|Particles smaller than 2.5 μm
|Lower Airways - Bronchioles and alveoli
After a particle is deposited, what happens?
First of all, the particle will either
- stay intact or
- dissolve (partially or completely)
If it dissolves, it's gone. Great!
If it stays intact or dissolved only partially it can do one of two things:
- go back outside the body
- go deeper inside the body
To remove it from the body your lungs are equipped with two different defense mechanisms:
-Mucus (“muco”) and Cilia (“ciliary”) in the respiratory tract move the particle back up and out of the respiratory tract
-Aided by coughing (to expel the particle), phagocytes (to ingest and destroy the particle), and other systems (eg. digestive system)
-Removes the majority of inhaled particles in the lower respiratory system
-Phagocytes (specialized cells) ingest and destroy the particle
-Primary means to remove particles that have made it all the way down to the alveolar region of the lower respiratory system
What about the particles that are not removed?
One of two things will happen
The particle will simply remain in the lungs.
Yes, that happens.
The particle is transported from the alveoli to the blood and from there it can go to any number of organs including the liver, spleen, kidneys, etc.
We do need to note here that this has been shown primarily in animal studies. Human studies have yet to show conclusive evidence of particle transport into the blood and into other organs.
A scientific look at the technical differences between allergens and particles
Allergens are the substances – the chemicals, if you will - that actually trigger the allergic reaction.
Particles are larger substances that transport the allergens.
Particles transport allergens in two different ways. They can
contain the allergens
we call particles of this type allergen containing particles
carry the allergens
we call particles of this type allergen associated particles
It is these particles that you need to remove from the air to prevent allergies caused by airborne allergens.
|allergen - glycoprotein
|e.g. cat allergen fel d 1
|Allergen containing particles
|e.g. pollen grain
|16 to >100 μm
|Allergen associated particles
|in the home - usually dust
|<1 to >100 μm
The best example of an allergen containing particle is a pollen grain. The smallest pollen grains are about 16 microns in diameter. A particle has to be 10 microns or larger to get stuck (land) in the upper airways for it to cause an allergic reaction. At 16+ microns pollen grains clear this 10 micron threshold quite easily.
But it’s not the pollen grain itself that triggers an allergic reaction. The pollen grain is deposited on a mucus membrane in your upper airways. The mucus is of a consistency that allows for the allergens inside the pollen grain to diffuse out of the grain and onto the membrane. This triggers a chain reaction that results in an allergic reaction.
The best example of an allergen associated particle is dust. The most common pet allergen is a cat allergen – fel d 1. This allergen – a glycoprotein – is found in the cat’s urine (among other places). When the urine dries the protein can associate with (latch onto) any number of particles around it. In the home, most particles around it are going to be dust particles. It is these dust particles that land in your upper airways and then release the allergens that cause an allergic reaction.
Dust particles can come from a number of sources and therefore run the gamut of <1 all the way up to >100 microns in size The end result is that fel d 1 in the home is associated with particles of pretty much all sizes and in order to completely protect yourself from fel d 1 you need to protect yourself from particles of all sizes.
The term “particle” and “allergen” is often use interchangeably. You could say that a particle is an allergen and an allergen is a particle.
And, technically, this isn’t incorrect. Any solid small “thing” can be called a particle. An allergen, even if it is extremely small, certainly fits this definition.
We only distinguish between allergens and particles here to show the difference between the substance that actually triggers an allergic reaction and the substance that transports it. It is this latter substance – the transport particle – that is the primary particle of concern.
It is these transport particles that carry or contain the allergens – not really the allergens by themselves – that need to be removed from the air to prevent allergies caused by airborne allergens.
But that is not to say that it isn’t perfectly acceptable to call a dust particle an allergen even if all it does is carry an actual allergen. It’s also perfectly fine to say that a pollen grain is an allergen even though all it does is contain allergens.
We just want to show you how you can be more specific with your language if you want to. For example, mold spores are often listed as allergens. This is not incorrect. Technically, the mold spore (2 to 40 microns in diameter) can be called an allergen. But more specifically, it can be called an allergen containing particle as it is not the mold spore itself that causes the allergic reaction but rather microscopic molecular level substances inside the mold spore that do it.
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