Ozone Generators: Why EPA and CARB Say Not to Use Them as Air Cleaners

An ozone generator is a machine that makes ozone on purpose and blows it into a room, usually sold to kill odors, mold or germs. EPA’s conclusion is blunt: at levels that don’t exceed public health standards, ozone has little potential to remove indoor air contaminants, and at levels high enough to work, it’s a lung irritant. No federal agency has approved ozone generators for occupied spaces, and California bans their sale as home air cleaners. We don’t recommend one for any room people or pets use.

This explainer is research-based, drawn from EPA’s ozone generator page and technical summary, California’s air cleaner regulation and ENERGY STAR’s specification. Our research method explains how we work.

What an ozone generator is

Ozone (O3) is a molecule of three oxygen atoms. The third atom breaks off easily and reacts with other substances, which is what sellers point to when they claim ozone “cleans” air. EPA describes it as a toxic gas with very different chemical and toxicological properties from the oxygen we breathe.

According to EPA’s technical summary, ozone generators sold as air cleaners use either UV lamps or electrical (corona) discharge to produce ozone, then a fan spreads it through the space. They’re sold as portable boxes and as duct-mounted units, and they’re usually marketed for odors.

EPA also flags the marketing language. Terms like “energized oxygen” or “pure air” suggest ozone is a healthy kind of oxygen; it isn’t. And the EPA establishment number printed on the box, required under federal pesticide law, only identifies the factory. EPA says it doesn’t mean EPA endorses the product or found it safe or effective.

What EPA found about ozone as an air cleaner

EPA’s page on ozone generators, last updated in February 2026, is the most direct source. Its main findings:

• It doesn’t work at safe levels. At concentrations that stay within public health standards, ozone has little potential to remove indoor air contaminants. Many indoor chemicals react with it so slowly that the process could take months or years.
• It doesn’t remove particles. Ozone does nothing for dust, pollen or other allergy-causing particles.
• It doesn’t remove some key gases. EPA says ozone isn’t effective against carbon monoxide or formaldehyde.
• It makes new pollutants. Ozone reacts with chemicals from cleaning products, air fresheners, paints, carpets and wood floors. EPA’s technical summary lists the byproducts as ultrafine particles, formaldehyde, ketones and organic acids. In one carpet study EPA cites, the total concentration of organic chemicals in the air went up after ozone was introduced.
• Odor claims are thin. Few studies support them, and some odors, like body odor, may simply be masked by the smell of ozone.
• Germ and mold claims need dangerous levels. EPA says ozone would have to be 5 to 10 times higher than public health standards allow to decontaminate air, and it may not reach contaminants inside porous materials.

Following the instructions isn’t enough

EPA describes a study where a generator was run on high in a 350 sq ft room and ozone quickly reached 0.50 to 0.80 ppm. In EPA’s own home study, some units run on high with interior doors closed often produced 0.20 to 0.30 ppm. Running more than one device, or adding outdoor ozone on a smoggy day, raises the risk further.

For scale, here are the limits EPA’s page cites, plus the current outdoor standard:

Limit	Value	Who sets it
Ozone output of indoor medical devices	0.05 ppm	FDA
Indoor air cleaners sold in California	0.050 ppm	CARB
Outdoor air, 8-hour average	0.070 ppm (set in 2015)	EPA
Workers, 8-hour average	0.10 ppm	OSHA
Workers, ceiling never to exceed	0.10 ppm	NIOSH

The levels measured in those studies ran four to sixteen times the FDA and CARB limits.

Health effects of breathing ozone

EPA says inhaled ozone can damage the lungs. Relatively low amounts can cause chest pain, coughing, shortness of breath and throat irritation. Ozone may worsen asthma and weaken the body’s defenses against respiratory infections, and exercise increases how much you breathe in.

Important: If someone in your home has asthma or another lung condition, keep ozone-producing devices out of the house entirely, and talk to your doctor if you’ve had symptoms after using one.

California’s rules (CARB)

Under the California Air Resources Board’s regulation (17 CCR 94800-94810), no one may make for use in California, sell or offer for sale any indoor air cleaning device unless CARB has certified it to emit no more than 0.050 ppm of ozone. That covers online sales too. A deliberate ozone generator can’t meet that limit, so it can’t be sold in California as a home air cleaner.

There is one exemption: industrial use. The regulation lets ozone machines be sold solely for listed uses where no people are physically present, including:

• Mold, odor, fire and smoke damage remediation services carried out by trained personnel
• Odor and smoke control in hotels, intermittent and temporary, by trained personnel
• Odor control in vehicle reconditioning and detailing, by trained personnel
• Microbe control on produce in agricultural plants and refrigerated trucks

Those machines must carry the advisory “For industrial use only. Use only in unoccupied spaces. Health hazard: emits ozone.” Their manuals must recommend ventilating the space for at least one hour before people go back in.

So when a restoration company “shocks” a smoke-damaged house with ozone, that’s this exemption: an empty building, a trained crew and a ventilation period afterward. EPA adds that conditions should be controlled so no person or pet is exposed, and that little is known about the chemical byproducts left behind. We’d leave ozone treatment to licensed professionals and keep people and pets out until they say it’s safe.

Ozone generators vs ionizers and other “electronic” purifiers

An ozone generator makes ozone as its main job. Ionizers, electrostatic precipitators, some UV lamps and plasma units can make ozone as a byproduct. EPA’s guide to air cleaners lists all of them as technologies that may emit ozone, and its technical summary notes that ionizers and precipitators don’t remove gases or odors.

The difference is control. Byproduct-ozone devices sold in California must be CARB certified at 0.050 ppm or less, and ENERGY STAR caps certified models at 50 ppb and excludes ozone generators from certification altogether. If a purifier you own has an ionizer, our guide to the ionic air purifier explains how to tell and how to switch it off, and our article on air purifier side effects covers ozone in more depth. Some “air scrubber” units use PCO and plasma stages; see air scrubber vs air purifier.

What to use instead

EPA’s advice is to use proven methods: control the source, ventilate and then clean the air. Here’s what we’d do for the jobs ozone generators are sold for.

• Odors and smoke smell. Find and remove the source, ventilate, and use a purifier with a substantial activated carbon filter. HEPA alone catches particles but not gases; our HEPA vs carbon filter guide explains why the amount of carbon matters, and our best air purifier for odor guide compares options.
• Mold. Fix the moisture problem and clean up the growth. EPA says a moldy area under about 10 sq ft can usually be handled by the homeowner; larger areas need more involved remediation. An air purifier can catch airborne spores but won’t solve mold. Our best air purifier for mold guide covers what filtration can and can’t do.
• Fire and smoke damage. Call a restoration company. If they use ozone, ask how long the building must stay empty and ventilated before you return.
• Germs and allergens. Filtration and ventilation do the work. A CARB-certified HEPA purifier sized for the room, plus a MERV 13 HVAC filter if your system can take it, will remove far more particles than ozone can at any safe level. Use our air purifier size calculator to match CADR to your room.

Houseplants aren’t the answer either:

Our take

We’d never run an ozone generator in a room where people or pets breathe, and we wouldn’t buy one for home use at all. The evidence runs one way: at safe levels ozone barely cleans, at effective levels it harms lungs, and in between it creates new pollutants such as formaldehyde. If a product promises “energized oxygen” or “pure air,” check the CARB certified list before you buy. In our view, carbon for odors, HEPA for particles and fresh air for everything else is the safer combination.