Ozone: Friend or Foe?

Depending on who you ask, you may hear ozone described as an air cleaner or a pollutant.  Some people buy machines to purposefully produce it to improve their health, and others avoid it because of the harmful effects on health.  To further confuse matters, we sometimes hear outdoor ozone referred to in a good light (the ozone layer) and other times in a bad light (as a component of air pollution).  In this short blog post, I will cut through the smog so you can better understand ozone.

What is it?

Ozone is also known as activated oxygen, allotropic oxygen, and triatomic oxygen.  It is comprised of three oxygen atoms (O3), whereas atmospheric oxygen is comprised of two oxygen atoms (dioxygen, O2).  Ozone is both naturally occurring and anthropogenic, meaning it is derived from human activities.  Naturally it can occur during a thunderstorm outdoors.  Indoors it is typically found as an incidental by-product of the following:

  • Electrostatic air cleaners
  • Photocopiers
  • Laser printers
  • Fax machines
  • Sewing Machines
  • UV Lights
  • Indoor hot tubs

So what is so good about ozone? Ozone can react with contaminants in the air and break them down via an oxidative process.  Ozone has been used successfully for years by professionals who restore smoke damaged personal items embedded with a residual odor.

So what’s so bad about ozone?  Here is a quote from the Environmental Protection Agency (EPA) regarding its health effects:

“The same chemical properties that allow high concentrations of ozone to react with organic material outside the body give it the ability to react with similar organic material 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.”


Ozone producing products should be avoided in spaces that are occupied by people or pets.  Even using these products in unoccupied spaces can have its risks:

  • In the presence of humidity, ozone may produce hydrogen peroxide and stain contents
  • In the presence of some VOCs like limonene and pinene, ozone can produce ultrafine particles
  • As ozone is breaking down organic compounds, intermediate chemicals can be produced that are worse than the originals
  • Ozone can oxidize rubber and soft plastics, damaging appliances and equipment

The final answer: Ozone is usually a foe.

By Ian Cull

I'm I.A.N. the Indoor Air Nerd. I'm a speaker and consultant on indoor air quality issues. To learn more about me, click "about" at the top of this page.

5 replies on “Ozone: Friend or Foe?”

I always get clients who have heard only about the benefits of ozone. I have always professionally recommended against the use of ozone for the treatment of mold.
What is the best pier reviewed document to support my recommendations?
Clinton J. Ford MS…

I think your best reference would be from the EPA’s website: ozone generators effective in controlling pollution.

It states, “Some data suggest that low levels of ozone may reduce airborne concentrations and inhibit the growth of some biological organisms while ozone is present, but ozone concentrations would have to be 5 – 10 times higher than public health standards allow before the ozone could decontaminate the air sufficiently to prevent survival and regeneration of the organisms once the ozone is removed (Dyas, et al.,1983; Foarde et al., 1997).

Even at high concentrations, ozone may have no effect on biological contaminants embedded in porous material such as duct lining or ceiling tiles (Foarde et al, 1997). In other words, ozone produced by ozone generators may inhibit the growth of some biological agents while it is present, but it is unlikely to fully decontaminate the air unless concentrations are high enough to be a health concern if people are present. Even with high levels of ozone, contaminants embedded in porous material may not be affected at all.”

Excellent article Ian. I’d heard many negatives with ozone treatments, but never their potential interactions with rubber and soft plastics. Interesting. I’ll add it to the ever growing list of reasons we don’t use it in our remediation practices.

P.S. Have you added a remediation training module to your course list?

Leave a Reply

Your email address will not be published. Required fields are marked *