Breathe Naturally - October 30, 2023

Air Purifier Filters for Allergies: What to Look For


Key Takeaways:

  • HEPA filters are the gold standard for trapping allergens and particulates. Look for True HEPA filters that remove 99.97% of particles 0.3 microns or larger.
  • Activated carbon filters adsorb odors, gases, and VOCs. Pairing activated carbon with HEPA improves overall air purification.
  • Ionizers and UV light purifiers can help destroy some biological allergens, but have limited effectiveness on particulates. They may produce ozone as a byproduct.
  • Consider the Clean Air Delivery Rate (CADR) rating when selecting an air purifier. Higher numbers indicate faster air purification for a given room size.
  • Replace filters per the manufacturer's recommendations, usually every 6-12 months with average use. Clogged filters reduce airflow and purification.
  • Run air purifiers continuously in rooms where you spend the most time. Use higher fan speeds when allergens are elevated.

With springtime comes blooming flowers, greening trees – and seasonal allergies for millions of people. Allergens like pollen, mold, dust mites, and pet dander can trigger symptoms of sneezing, coughing, itchy eyes, runny nose, and more.

While over-the-counter medications can help relieve some misery, using an air purifier is one of the best ways to filter allergens directly from the air inside your home. But not all air purifiers are equally effective for allergies. Understanding the different technologies and what specifications to look for can help you choose the right model.

HEPA Filters: The Gold Standard for Allergens

HEPA (High Efficiency Particulate Air) filters are considered the best for trapping airborne particles that cause allergic reactions. True HEPA filters are rated to remove 99.97% of particulates 0.3 microns or larger (1). For reference, a human hair is about 50-70 microns wide, while pollen ranges from 10-100 microns. Mold spores are around 3-40 microns, and pet dander 2.5-10 microns. So HEPA filters capture the majority of these common allergens from the air flowing through them.

The tightly packed glass fibers in HEPA filters create a dense web that ensnares particulates and prevents them from passing through. As air circulates through the filter, allergens become trapped rather than recirculated into the room. This can provide significant relief, especially when used continuously in bedrooms or frequently occupied rooms. Look for the words "True HEPA" when evaluating air purifiers, as not all HEPA-type filters meet the specifications for 99.97% effectiveness down to 0.3 microns.


It's also important to note square footage guidelines for HEPA air purifiers.

Manufacturers assign a Clean Air Delivery Rate (CADR) rating, which measures the cubic feet per minute (CFM) of filtered air delivered for a given room size (more on this later). Running an undersized air purifier will reduce its ability to fully filter the air volume. HEPA filters are also more effective when air can pass through slowly, allowing time for particles to get caught. So bigger is generally better when it comes to HEPA filtration.

Combining HEPA with Activated Carbon

While HEPA air filters excel at trapping solid particles, they do little for gases like volatile organic compounds (VOCs) or odors. That's where combining them with activated carbon filters helps. The incredibly porous structure of activated carbon acts like a sponge to adsorb gases, fumes, and odors as air passes over it. This includes VOCs from cleaners, furniture, paints, carpets and building materials, which can exacerbate allergy and asthma symptoms for sensitive individuals (2).

Adding an activated carbon prefilter helps remove these irritants before air reaches the HEPA filter. Activated carbon also helps control musty "basement smells" that could be an indicator of mold. Using both filter types creates a more comprehensive air purification system.

 Some air purifiers stack a HEPA filter behind one or two activated carbon filters for this targeted two-step cleaning. Filters specifically made with activated carbon impregnated into a HEPA substrate provide both functions in one.

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Understanding Ionizers and UV Light Purifiers

Other technologies like ionizers and UV light air purifiers take a different approach. Ionizers work by charging airborne particles with negative ions. These ions cause particles like dust and pollen to stick together and become heavier, dropping them out of circulation. UV light units use short-wave ultraviolet light to alter the structure of biological allergens like mold, bacteria, and virus particles so they can no longer reproduce (3).

However, ionizers and UV light air purifiers have downsides and limits on effectiveness. Ionizers are not as efficient at removing fine particles below 0.3 microns. There are also concerns that they can generate ozone, a lung irritant, as a byproduct (4). UV light systems only work on air flowing directly through the unit, so they sanitize a smaller percentage of total air volume. And neither technology physically traps or filters particles from the air – they remain in the room even if damaged or inert.

For these reasons, ionizers and UV purifiers work best alongside HEPA filters that can capture the neutralized particles. Used alone, they are less reliable for controlling allergen exposure. And neither system eliminates odors or gases the way activated carbon absorption does.

Pay Attention to the CADR Rating

When comparing air purifiers, look closely at the Clean Air Delivery Rate (CADR). This performance rating designates the cubic feet per minute (CFM) of purified air produced, measured by independent testing labs. CADR ratings are assigned for tobacco smoke, dust, and pollen particulate removal. The higher the number, the faster the unit filters the air.

Manufacturers size recommendations for room coverage are based on the CADR rating. For example, an air purifier with a pollen CADR of 200 is suited for rooms up to 325 square feet, while a CADR of 400 covers rooms up to 665 square feet. In general, units under 200 CADR are best for small rooms and supplemental use. Medium models with CADR 200-300 work well in bedrooms. Large models over 300 CADR are ideal for open floor plans and main living areas.

Running an undersized air purifier may mean it can’t fully exchange and filter the air volume required. It's best to pick a model rated for at least 2/3 the size of the room. So if your bedroom is 150 square feet, look for a purifier with a CADR of 100 or more. This ensures the unit can fully circulate and clean the air multiple times per hour.

Maintaining Air Purifiers for Peak Performance

To work effectively, air purifiers require regular filter maintenance according to manufacturer guidelines. For HEPA filters, this is generally every 6-12 months with average use. Heavy use or highly polluted environments may require more frequent replacement. Many air purifiers have filter life indicators that display when it’s time to change filters based on hours used or air resistance.


It's important not to wait until filters look visibly dirty, as particulate filters will appear clean until they become densely clogged. Slow airflow and reduced particle removal indicate filters are overdue. Activated carbon filters may need replacement more often than HEPA filters, as they eventually become saturated and lose adsorption capacity.

Proper maintenance also includes cleaning the unit exterior about once a month to prevent dust buildup that impedes airflow. Always turn the air purifier off and unplug it before cleaning. Follow manufacturer guidelines on any special cleaning requirements.

Positioning Tips for Air Purifiers

Where and how you operate an air purifier affects its particle removal. Keep the following tips in mind:

  • Place air purifiers in rooms where you spend the most time, such as bedrooms, living rooms, and offices.
  • Don't obstruct air intake or output. Allow at least a foot clearance on all sides.
  • Position an air purifier near seating areas to filter air right where you breathe.
  • Run the air purifier continuously at a low or medium fan setting. The more air it processes, the better.
  • When allergens are high, use the highest fan speed and keep doors/windows closed.
  • Use the auto mode, if available, to let the unit self-adjust based on air quality sensor feedback.
  • Add multiple air purifiers for very large, open floor plans.
  • Don't rely solely on air purifiers to filter attached garages, basements, or widespread sources.

Investing in quality HEPA air purification can literally help you breathe easier during allergy season. Paying attention to key specifications and using proper maintenance practices will keep your unit working optimally. Position air purifiers strategically to filter the air where you need it most. By removing airborne allergens circulating indoors, air purifiers can be indispensable for better springtime breathing.