Problems with Ozone Generators and Ionizers that Produce Ozone

"Ozone is a potent lung irritant and exposure to elevated levels is a contributor to the exacerbation of lung disease; it is especially dangerous for persons with asthma and other chronic lung diseases, children and the elderly."

American Lung Association (

Residential indoor ozone is produced directly by ozone generators and indirectly by ion generators and some other electronic air cleaners. There is no difference, despite some manufacturers' claims, between outdoor ozone and ozone produced by these devices.

The Environmental Protection Agency (EPA) has done extensive research of the most credible scientific information available on the effects of ozone and the devices that generate ozone. This can be found at The following is an excerpt from this document.

What is ozone?

Ozone is a molecule composed of three atoms of oxygen. Two atoms of oxygen form the basic oxygen molecule — the oxygen we breathe that is essential to life. The third oxygen atom can detach from the ozone molecule, and re-attach to molecules of other substances, thereby altering their chemical composition. It is this ability to react with other substances that forms the basis of manufacturers' claims.

How is ozone harmful?

The same properties that allow high concentrations of ozone to react with organic matter outside the body give it the ability to react with similar organic matter that makes up the body, and potentially cause harmful health consequences. When inhaled, ozone can damage the lungs. Relatively low amounts can cause chest pain, coughing, shortness of breath and throat irritation. Ozone may also worsen chronic respiratory diseases such as asthma and compromise the ability of the body to fight respiratory infections. People vary widely in their susceptibility to ozone. Healthy people, as well as those with respiratory difficulty can experience breathing problems with exposure to ozone. Exercise during exposure to ozone causes a greater amount of ozone to be inhaled, and increases the risk of harmful respiratory effects. Recovery from the harmful effects can occur following short-term exposure to low levels of ozone, but health effects may become more damaging and recovery less certain at higher levels or from longer exposures (US EPA, 1996a, 1996b).

Are ozone generators effective at controlling indoor air pollution?

Available scientific evidence shows that at concentrations that do not exceed public health standards, ozone has little potential to remove indoor contaminants. First, a review of scientific research shows that for many of the chemicals found in indoor environments the reaction process with ozone may take months or years (Boeniger, 1995). Second, for many chemicals with which ozone does readily react, the reaction can form a variety of harmful or irritating by-products (Weschler et al., 1992a,1992b,1996; Zhang and Lioy, 1994). Machines that generate ozone are not effective in removing carbon monoxide (Salls, 1927; Shaughnessy et al., 1994) or formaldehyde (Esswein and Boeniger, 1994). In fact, when tested on new carpet odors and gasses, the reaction with ozone actually increased the number of aldehydes and volatile organic compounds (Weschler et al., 1992). Some of these new compounds created through the reaction with ozone are very reactive, irritating and a potential health threat. Third, ozone does not remove particles (e.g., dust and pollen) from the air, including the particles that cause most allergies. However, some machines that generate ozone also produce ions. An ionizer is a device that disperses negatively (and/or positively) charged ions into the air. These ions attach to particles in the air giving them a negative or positive charge so that the particles may attach to nearby surfaces such as walls, furniture or each other and settle out of the air. Some units also have internal "plates" that help gather particles. In recent experiments, ionizers were found to be less effective in removing particles of dust, tobacco smoke, pollen or mold spores than either HEPA filters or electrostatic precipitators. (Shaughnessy et. al, 1994)

If a machine does not emit more than 50 parts per billion allowed by the EPA, can it still be harmful?

Yes, there is no "safe" level of ozone. For many people, even at the 50 parts per billion of ozone allowed by the EPA, exposure far exceeds the tolerance level.

However, there are also other factors that contribute to ozone levels. First is the size of the room where the machine generating ozone is being used. In one study a machine run in a 350 square foot room generated ozone counts in the room of 500 to 800 parts per billion — ten times the allowable limit. Second, indoor air generally contains some ozone — particularly when ozone is at high levels in the outdoor environment. Indoor ozone concentrations generally run at 10 to 20 parts per billion, but can be as high as 30 to 50 parts per billion. When you add the ozone coming from a machine, it would most certainly exceed allowable limits. Third, the simultaneous use of multiple devices greatly increases the total ozone output and therefore greatly increases the risk of excessive exposure.

The US Food and Drug Administration also addresses the issue of the labeling of machines that generate ozone. In the Code of Federal Regulations, Title 21, Volume 8, Part 801 ( it states:

"A number of devices currently on the market generate ozone by design or as a byproduct. Since exposure to ozone above a certain concentration can be injurious to health, any such device will be considered adulterated and/or misbranded within the meaning of sections 501 and 502 of the act if it is used or intended for use under the following conditions:

  1. In such a manner that it generates ozone at a level in excess of 50 parts per billion by volume of air circulating through the device or causes an accumulation of ozone in excess of 50 parts per billion by volume of air in the atmosphere of enclosed space intended to be occupied by people for extended periods of time, e.g., houses, apartments, hospitals and offices. This applies to any such device, whether portable or permanent or part of any system, which generates ozone by design or as an inadvertent or incidental product.

  2. To generate ozone and release it into the atmosphere in hospitals or other establishments occupied by the ill or infirm.

  3. To generate ozone and release it into the atmosphere and does not indicate in its labeling the maximum acceptable concentration of ozone which may be generated as established herein and the smallest area in which such a device can be used so as not to produce an ozone accumulation in excess of 50 parts per billion.

  4. In any medical condition for which there is no proof of safety and effectiveness.

  5. To generate ozone at a level less than 50 parts per billion by volume of air circulating through the device and it is labeled for use as a germicide or deodorizer." (Revised as of April 1, 2003)


  1. Whether in its pure form or mixed with other chemicals, ozone can be harmful to health. When inhaled, ozone can damage the lungs. Relatively low amounts of ozone can cause chest pain, coughing, shortness of breath and lung irritation. Animal studies suggest that long term exposure to ozone may lead to permanent scarring of lung tissue, loss of lung function and reduced lung elasticity. It may also worsen chronic respiratory diseases such as asthma and COPD. Machines that generate ozone should never be used around the ill, infirm, young or elderly.

  2. Many factors affect ozone concentrations produced by machines that generate ozone including the amount of ozone produced by the machine(s), the size of the indoor space, the amount of material in the room with which ozone reacts, the outdoor ozone concentration and the amount of ventilation. These factors make it difficult to control ozone concentrations.

  3. Available scientific evidence shows that, at concentrations that do not exceed public health standards, ozone is generally ineffective at controlling indoor air pollution. In the process of reacting with chemicals indoors, ozone can produce other chemicals that themselves can be irritating and corrosive.

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