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Updated by Molekule staff 5/15/23


You may have heard this before from our previous articles on indoor air pollution, but it’s worth repeating: we spend the majority of our time indoors, 90% on average to be precise. Because of this, indoor allergens and irritants are an increasingly important factor when it comes to asthma symptoms and triggers.

If you or your loved ones are suffering from asthma and you have been looking for an air purifier as a solution, you may have come across manufacturers marketing ionizer and ozone generators as a solution for asthma sufferers. Unfortunately, many of these are false promises and could even add triggers to your air that increase the frequency of your asthma attacks.

Close up of particles in air

Indoor air quality and asthma triggers

To understand how existing air purification technologies, like HEPA filters, ozone generators, and air ionizers may not alleviate asthma attacks and symptoms, you will first have to understand the relationship between indoor air quality and asthma triggers. What types of pollutants are known asthma triggers? Which irritants can make your asthma symptoms worse? Let’s take a look at some of the most common asthma triggers.

diagram of common asthma triggers in homes


The EPA says that ozone pollution is more problematic for people with asthma than for those without. Ozone can penetrate the home from outside where it is generated from the interaction of car exhaust, industrial pollution, and sunlight. People who are sensitive to asthma triggers already are likely to be even more sensitive when ozone concentrations are higher. Even people who aren’t may experience chest pain, coughing, shortness of breath along with throat irritation when exposed to ozone.

Dust mites

While your eyes may not be able to see them, house dust mites abound and reside in every home (typical size measures 0.2 to 0.3 millimeter). Dust mites feed on human skin flakes and can often be found in common household objects such as mattresses, pillows, clothes, stuffed toys, and almost any fabric covered items.

Dust mites along with dust mite droppings can trigger asthma for those that are allergic to dust mites. Much like many other asthma triggers such as cockroaches, frequent exposure to dust mites can cause asthma to develop in children.

Secondhand smoke

Smoke exhaled by a tobacco smoker (cigarette, cigar, or pipe) is considered secondhand smoke. Beyond containing over 4,000 substances, many of which lead to cancer – these secondhand smoke irritants can trigger asthma episodes and increase the severity of attacks. Worse, secondhand smoke is a risk factor for the development of asthma in preschool-age children.


Molds are microscopic fungi that reproduce by creating tiny spores. They float through the indoor air and may grow in damp places. If you are hyper-sensitive, have asthma, or are otherwise sensitive to mold, inhaling mold spores can trigger an asthma attack. Worst yet, the National Academy of Medicine (formerly known as the Institute of Medicine) has found that there is sufficient evidence that links indoor exposure to mold with upper respiratory tract symptoms including coughing and wheezing – even in healthy people. It is even possible to acquire a mold allergy with frequent exposure.

Chemical pollutants (VOCs)

Found in almost every home, asthma symptoms may be triggered and become worse around certain chemical cleaners, paints, adhesives, pesticides, cosmetics, or even air fresheners. These pollutants and irritants, particularly the ones with strong scents such as cleaning supplies along with scented candles and incense – can affect a person with asthma.

Nitrogen dioxide (NO2)

Whenever natural gas is burned nitrogen dioxide, or NO2, fills the air. Because it also comes from other fossil fuels like gasoline and coal, NO2 is one of the EPA’s criteria pollutants. In addition to being an irritant, the risk of children developing asthma in a house with a gas stove is similar to the risk in a house with a cigarette smoker. If you or your family is prone to asthma, a well-vented gas stove is a must.

Air purifiers to avoid if you have asthma

Now that you are familiar with some of the major asthma triggers, you’ll need to examine why two particular types of air purifiers, namely ionizers and ozone generators are products you should avoid as an asthma sufferer.


Though they come by many names, negative ion generator, needle-point ionizers, bipolar ionizer, or others, these devices are designed to severely unbalance the electrical charge of air molecules, and a molecule with a severely unbalanced charge is an ion. The principle is that these charged ions will then attach to pollutant particulates in the air that are less mildly charged, in turn unbalancing their charges to a greater degree. Then charges on the particles are supposed to attract them to surfaces like static electricity (which usually doesn’t result in ionization) for easier collection.

Unfortunately, studies have shown that ionizers are not very effective in removing particles of dust, tobacco smoke, pollen grains, or fungal spores – all potential triggers for asthma sufferers. Not only are charged particles that stick to the walls and floor are easily stirred up again, but they also stick better to your lungs when inhaled.

Even if they aren’t spreading charged particles ionizers can generate ozone. Despite being a product that produces harmful ozone, ionizers are still often positioned as a solution for allergy and asthma sufferers – if you or your loved ones suffer from asthma, you can help spread awareness and educate other sufferers on these products. 

There are ionizers that don’t generate ozone and use a combination of filters to avoid spreading charged particles. All air purifiers sold in California must be ozone-safe, so a good place to check before you consider a purifier is this list of approved air purifiers on the California Air Resources Board website. You can also look for an official ozone-free seal by UL, Intertek, or other Nationally Recognized Testing Laboratory (NRTL).

Ionizers that don't spread charged particles will not advertise that they do. While the word “ionizer” might be on the package, it should be clear that all ions are blown into a filter, not into the air. These purifiers are just using the attraction of static electricity to improve efficiency.

Chart showing different ozone safety levels

Ozone generator

This form of air purifier is a stark contrast to what any asthma sufferers should be seeking – as the very purpose of the device is to intentionally produce ozone. Despite years of health professionals refuting manufacturer claims that ozone generators can be a method to control indoor air pollution, the product is still being positioned as an indoor air purifier – and one that asthma sufferers may purchase.

While many manufacturers of ozone generators may include an EPA number on the packaging, this does not mean they are approved by a government body. While official looking, these EPA numbers are simply identification numbers for where the device was manufactured – and does not mean an EPA endorsement because there are no air purifiers officially endorsed by the EPA. In fact, many ozone generators will even have disclaimers and cautions on the device informing consumers that the product should not be used in occupied spaces.

While manufacturers will claim that ozone generators can eliminate indoor air allergens by creating a chemical reaction with the pollutant particulates (creating only safe byproducts), this is misleading because ozone by itself will not remove particles such as dust or pollen from the air, two particles that frequently causes allergies and asthma.

In their concluding report on ozone generators, the EPA has stated clearly that ozone generators are harmful to health and can worsen chronic respiratory diseases such as asthma, and compromise the ability of the body to fight respiratory infections. Some purifiers, such as some UV-C TiO2 devices, may produce ozone without advertising that fact. Like with ionizers, check that the air purifier is listed as ozone-safe on the California Air Resources Board website, or has an official ozone-free seal by UL, Intertek, or other (NRTL).

Vacuuming a mattress

A better solution: avoid and reduce triggers in your home

Instead of looking to air ionizer or ozone generators as a solution to your asthma (they are not), the most cost effective method still resides in avoiding and reducing asthma triggers in the first place. Here are some actions you can take based on the four triggers we mentioned above:

  • Dust mites: for those with severe asthma, you should wash your bedding in hot water (130F or higher to kill mites) regularly once a week. Using dust-proof covers on pillows and mattresses will also reduce dust mites significantly. As part of the weekly cleaning regimen, you should also regularly vacuum carpets and upholstery furniture. Open your windows if possible while vacuum cleaning. For those with children suffering from asthma, choose stuffed toys that can be washed in hot water vs. those that can’t.
  • Gas stoves: Strongly consider getting an electric or induction range if asthma is a concern. An electric range is no more than $500 and installation will require at most another circuit which runs from about $700 to $1000. Induction ranges offer a better cooking experience but will cost 3-4x more for the range with the same installation costs. If gas is necessary, be sure it is vented outside or always have a window open when cooking.
  • Secondhand smoke: if your child has asthma, avoid exposure to smokers near your child and ask them to smoke outside to avoid introducing secondhand smoke indoors. This is especially true for secondhand smoke in cars because smoke residue can settle and remain for a long time in small enclosed spaces.
  • Mold: The best way to combat the buildup of mold is by eliminating sources of moisture and to keep the humidity level between 30%-50% in your home. If you have a known leak in the bathroom that’s seeping into the drywall, fix the leak before mold starts growing on the drywall. Once mold is growing on drywall, it can be quite complicated to eliminate every point of growth, particularly for unpainted drywall as they have a porous surface. Regularly using exhaust fans or opening the window when showering in the bathroom are also good ideas. In fact to automate things a bit – look into replacing your fan switch to one that will automatically turn-on based on the humidity level in the bathroom.
  • Chemical pollutants: Avoid using aerosol spray and cleaning products such as chlorine bleach, or products that contain ammonia as these have been found to have the highest occurrence in impacting an asthma sufferer. If you must use these products, ensure the enclosed space is well ventilated by opening windows or doors and introducing outdoor air. You should also consider choosing cleaning and personal care products that are odor and fragrance-free to reduce the chances of asthma triggers from odors.
  • Utilize air cleaners: While HEPA filters can effectively remove from the air particles such as dust and pet dander, a HEPA air purifier can only filter and trap potential allergens. At Molekule, we’ve developed a new technology that can destroy allergens at the molecular level.

For more details on indoor air pollution and ways to combat it, click here. For more resources on ways to reduce allergy triggers, the CDC also has a helpful brochure on controlling asthma, available here to download.

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