Does Ozone Kill Mold and Is It Safe?

This post may contain affiliate links. Read our full disclosure.

Park yourself in just about any online mold forum, social media group, or chat and you will see a lot of support for the use of ozone to kill mold. Does ozone kill mold? Is it safe to use? Let’s dive into what is a very controversial and loaded topic. I will do my best to keep it simple by breaking this post into digestible parts.

What is Ozone?

Ozone is the principal element of the ozone layer, which traps the sun’s heat and is essential to life on Earth. Unlike breathable, stable oxygen molecules, which are composed of two oxygen atoms, ozone is composed of three. The third oxygen atom in ozone can easily detach from the ozone molecule and reattach to other substances, altering their chemistry.

What Produces Ozone?

In order to use ozone to kill mold, you must start with an ozone generator. Ozone generators intentionally produce the toxic gas ozone and are sold as air cleaners for commercial and residential applications. Specifically, they are advertised to deodorize, disinfect, kill or remove dangerous or irritating airborne particles in indoor environments including mold.

Ozone generator

How Do Ozone Generators Make Ozone To Kill Mold?

Ozone generators produce the gas in large enough quantities that unstable organic compounds will react with the gas and, supposedly, be altered so that they will no longer be irritating or dangerous. Since ozone is composed of three oxygen molecules, it can combine itself with things like mold and mold spores. It will change them in such ways that it kills the spores and cells that compose the mold.

In more scientific terms, ozone generators make ozone by breaking apart oxygen molecules, a process that can be accomplished in the following ways:

Silent Corona Discharge

All electrical discharges, such as lightning, produce ozone by splitting normal oxygen and creating single oxygen atoms, which then attach themselves to O2 to form ozone (O3). Silent corona discharge-ozone generators operate by this principle.

Ultraviolet Radiation

This process is similar to the formation of ozone in the upper atmosphere, where the sun’s ultraviolet radiation causes O2 to split into individual oxygen atoms. This method is generally regarded as less efficient than corona discharge.

Does Ozone Kill Mold?

Yes, technically ozone kills mold. But there are a LOT of limitations.

Ozone does not penetrate walls, floors, or other surfaces. While it can get into nooks and crannies, ozone can only tackle air born mold and surface mold. Ozone can only go where air can go. As I am sure you are aware, mold is never just in the air.

Ozone will not remove the mold spores it just rendered inactive nor will it kill the mold spores that are growing deep down into building materials and household items. Mold remediation including properly removing the moldy materials and items still needs to be completed.

Using ozone to kill mold does not correct the conditions that allowed the mold to grow in the first place. You have to fix the leak or address the cause of moisture intrusion before you begin dealing with the resulting mold.

In fact, using ozone to kill mold is pointless if you haven’t addressed the root cause and removed all the moldy building materials and household items. As soon as you disturb the mold, spores will go flying and you will recontaminate your home or the contained area.

Ozone typically isn’t used before remediation. There are two exceptions however.

  1. If you can’t address the mold problem right away, ozone will halt mold growth for a very short period of time.
  2. Ozone works well as an antimicrobial treatment prior to disturbing mold during remediation.  This helps to prevent any inadvertently transported spores from being able to reproduce in other areas by deeming them nonviable (dead). This is typically only done when the area being remediated can’t be effectively contained or is in an area of the building where access requires a lot of movement through other parts of the building.

But wait – before you start thinking that ozone treatments are a good idea… consider this.

The amount of ozone it takes to truly kill mold is so toxic it will kill you too. Therefore, you would need to stay out of your home for several days if not a week after treatment.

This also means that the vast majority of ozone generators available for sale or to rent to the general public are NOT powerful enough to produce the amount of ozone needed to effectively kill mold.

In addition, ozone treatments for mold need to be done in an airtight environment. This means that your house would need to be completely sealed up. No gaps around exterior doors or windows, all attic vents sealed, cracks and crevices closed up, etc… Most homeowners and remediation companies won’t go through all this effort. And effort it is.

Ozone generator for mold removal

Does ozone kill mold occurring to the EPA?

This is straight from the EPA’s website.

Available scientific evidence shows that at concentrations that do not exceed public health standards, ozone has little potential to remove indoor air contaminants. Some manufacturers or vendors suggest that ozone will render almost every chemical contaminant harmless by producing a chemical reaction whose only by-products are carbon dioxide, oxygen and water. This is misleading. The EPA does not certify or endorse any air cleaning devices or recommend air cleaning devices or manufacturers.”

Health Considerations When Using Ozone To Kill Mold

Unfortunately, the same chemical properties that allow ozone to alter organic material in household air also give it the ability to react with organic material inside the human body. Ozone’s chemical reactivity does not stop when it enters the body. It continues to release the extra oxygen atom, which damages cells. This released oxygen atom is an oxidizer, the opposite of an anti-oxidant that we might take to improve health.

These well documented scientific and medical facts form the basis for a number of health risks related to ozone. Four different government agencies have restrictions on ozone exposure, including the Food and Drug Administration (FDA), the Occupational Safety and Health Administration (OSHA), the National Institute of Occupational Safety and Health (NIOSH), and the Environment Protection Agency (EPA).

These agencies agree that low levels of ozone exposure can cause the following conditions:

  • Coughing
  • Chest pain
  • Shortness of breath
  • Wheezing
  • Throat irritation
  • Worsened chronic respiratory diseases such as asthma
  • Increased risk of developing bronchitis or pneumonia
  • Compromised ability of the body to fight respiratory infections

There are a lot of other known health risks associated with ozone exposure but the above list are the most concerning.

The EPA notes that it is increasingly difficult to determine the actual concentration of ozone produced by an ozone generator because so many different factors come into play. Concentrations will be higher if more powerful devices are used in smaller spaces. Whether or not the interior doors are closed rather than open will affect concentrations as well. Additional factors which affect concentration levels include how many materials and furnishings are in the room to react with ozone, the level of outdoor air ventilation, and the proximity of a person to the ozone generating device. This means that you don’t really know how much ozone is left lingering in your indoor air.

It is VERY important to note that ozone can dull the olfactory sense, a fact that has led many experts to believe that ozone’s deodorizing abilities are at least partially due to an altered odor perception, rather than any change in the environment. So this means that just because you can’t smell mold doesn’t mean you have really removed mold.

Potential Damage To Items In A Home From Using Ozone To Kill Mold

Did you know that using ozone to kill mold can actually CREATE horrible odors? Yes, ozone is touted as a magic cure for odors but in fact, it can actually create new, nasty, toxic odors.

Basically if you are using ozone for mold then you likely are going to cause materials to oxidize. Here are some examples of materials that are known to give off obnoxious smells after misuse of an ozone generator. And by misuse I mean running an ozone generator too long and/or at too high a setting in too small a space.

  • Carpet
  • Carpet padding
  • Fabrics
  • Foam anything
  • Most cushions
  • Plastics
  • Rubber
  • Items that have been painted or stained
  • Electrical wire coatings
  • Fabrics and art containing certain dyes or pigments

In addition to these materials giving off a horrible (irreversible odor), ozone is known to damage these materials to the point of rendering them useless.

Ozone generators can also damage plants in indoor environments. High levels of ozone will inhibit the ability of plants to open the microscopic pores on their foliage and breathe. Specifically, ozone can cause the following conditions in plants:

  • Chlorosis, a condition in which the plant cannot produce sufficient chlorophyll to manufacture carbohydrates
  • Necrosis which may lead to the death of the plant as a whole;
  • Flecks or small irregular spots
  • Small, darkly pigmented areas
  • Reddening

Other Risks Of Using Ozone To Kill Mold

People’s susceptibility to ozone varies widely. An ozone generator should never be operated in occupied spaces, and the area should be adequately vented before people or animals are allowed to re-enter.

According to a report produced by the EPA, ozone generators are ineffective at reducing levels of formaldehyde and carbon monoxide, despite claims by manufacturers. Also, from the toxins with which ozone does react, there is a potential for the creation of new, potentially more dangerous toxins. For example, ozone mixed with chemicals from new carpet can create aldehydes, which can irritate the lungs. Other reactions may create formic acid, another irritant. The potential for chemical reactions in the average house is difficult to predict.

Ozone treatments will not prevent mold from growing in the first place.  A lot, and I mean a lot of people have a false sense of security that if they used ozone to kill mold it will also prevent it.

So Ozone Isn’t The Safest Or The Best Way To Kill Mold. What Is The Alternative?

The following alternatives can be used to deal with an indoor mold situation:

Using HEPA vacuums and HEPA air purifiers are also a good mold prevention plan but are not a substitute for proper mold removal efforts.

If you have outdoor mold, please visit my post about how to remove and prevent outdoor mold for more information on how to tackle that.

Ozone generator for mold removal

Notable references include:

Photo Credit – Ozone Graffiti:

Leave a Reply

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


  1. What is your professional opinion on the use of Concrobium in a fogger ? I have black mold on the underside of my roof in a unfinished attic. Northern exposure with mature trees ( Shade) The roof is in excellent condition- no leaks/ deterioration. I will have to wait until above 50* to do this to be effective.
    The Concrobium fogging that is.
    Your opinion- Please

    1. Concrobium is not my first choice to fog with because it does not do anything about mycotoxins. However, a lot of people use it with success. My personal choice is this product line:

  2. We moved out of a moldy home 2 yrs ago and changed states to a drier climate. Tossed or donated all our furniture and the very little we brought with us were items that had been washed with the ec3 laundry additive or wiped with the ec3 mold solution.

    However, we have some impt paperwork and sentimental items like photos and scrapbook albums that I couldn’t just toss. While none of these items had actual mold growth on them, I worry that mycotoxins from the room could have seeped into these porous items, or loose spores floating in the room could have landed on these items. Yet these can’t be fogged or wiped or washed. And the last thing I want to do is re-introduce mold to our new house via our belongings.

    My naturopath had suggested we could put these items in a large plastic bin and run an ozone generator for a few hours to kill any potential/lingering mycotoxins or spores. But I’ve also read that ozone doesn’t mix well with paper and plastics. (My scrapbook album pages are in plastic sleeves, but the reason I still worry they got contaminated with mold is because the top side of the sleeve is open, and my albums sat on an open shelf for years, in this room where mold was found under the carpet. So dust/mold spores that fall on horizontal surfaces likely collected on the top ridge of each scrapbook album page that was not protected by plastic).

    Sorry for this long explanation. My main question is: is it safe to run these albums through an ozone generator? If not, do you have any other suggestions for how I could clean/disinfect my photo album and scrapbook pages and remove mycotoxins and/or loose spores before bringing them to my new house?

    Thank you so much. This has been a grueling and painful journey of many health issues and much loss. It was so refreshing to know that you have experienced something like this before and can relate!

    1. Hi Lily! So sorry that you are having to go through all this. When I left my moldy home I struggled with paperwork and photos. Let’s just say that I tried everything to save them. Ultimately I placed important paperwork in a plastic tote and stored it in the garage. If I needed to access it I lugged it outside and opened it there. I decided to send all my photos into a company to scan them and save them digitally. The same could be done with scrapbook pages. It wasn’t cheap but I didn’t feel safe doing anything differently. My health was more important. If you prefer not to do that, I would not bring these into your home. Wipe each picture / page with a cloth and then store them in a plastic tote you keep in the garage and forget about them for a decade. Not kidding. I did this with ONE photo album and opened the tote 5 years later. I reacted immediately. Mycotoxins are no joke. Scanning is truly your best bet. Please reach out if you would like more info! Happy to help!

    2. Sunlight kills mold. Put the contaminated items outdoors in direct sunlight for a few hours. I’ve done this personally and effectively decontaminated clothing that contained the cardboard mold species.

      1. A word of caution – while sunlight does destroy SOME species of mold, it does not destroy ALL species of mold. Sunlight alone also doesn’t work. You can’t put something covered in mold outside and expect that the mold will vanish. You still need to remove the mold first. In addition, sunlight on a cold day won’t work. You need higher temperatures as well. Also remember that this will onyl help with items that can be brought outside. If your house has a mold issue on building materials, you need to address that.

  3. Are the EC3 candles effective at getting rid of the micro toxins? Do carbon filters also capture micro toxins? I bought the ozone machine, if we find all sources of mold and mitigate them, then would it be prudent to run the ozone for only say 30 min per room so as to not cause off gassing from carpet or electric wiring? We can remove most other materials. Our mold professional said he would fog with peroxide and vinegar which i thought sounded like the best solution but our naturopath warned he had patients then suffer from chemical off gassing after that treatment. Any thoughts on that sort of fog treatment?

    1. Hi Jennifer! Yes, the EC3 candles are designed to tackle mycotoxins as well as mold spores. Mycotoxins are the most difficult thing to get rid of and to date, there is no type of filter that has been independently tested and proven to capture mycotoxins. There are different types of peroxide which can be effective on mold but honestly, fogging with peroxide and vinegar isn’t my favorite option. Peroxide can be very difficult on your respiratory health.

  4. Hi Jenifer: My bedroom was exposed to mold from the ceiling of my closet. After remediation I did not remove the pictures and items that were in the drawers of my furniture. The remediation company told me that they have wiped the furniture. I don’t know if that is even possible to work. I want to know all the items that are in the drawers are also contaminated? After remediation they checked the air and told us things are good but I don’t know if it was the right way to check.

    Also, I just find out from a urine test that my MYCOPHENOLIC ACID that was 1.40 and 3.50 in 2020 now it is 1068. I am shocked and don’t know how I am getting this mycotoxine.
    I am sorry to take your time but I don’t know who to ask. I just find you and I wanted to use ozone machine but after reading your site, I decided to wait.
    Thank you so much for your help.

  5. Please address the ozone machines for washing machines! Do you believe they are effective? I bought one, but still feel some clothing items stink–they’ve been going in the garbage! The instructions say that the colder the better. Well, we live in a very cold climate in the winter. I Have been tossing clothes and undergarments because the elastic is shot, or it looks like the fabric is internally exploded and items I’ve cared for for years are covered in pilling! I always thought very cold water was the most gentle for clothes, but found one comment that extremely cold water, even wothout ozone, is damaging. I cany’t find any answers to that question, either. The EC3 is just sooo expensive for mold per load, but is this really the only thing that works? Thank you for sharing your expertise!

  6. Anita Gonzalez says:

    In addition to dusting and vacuuming, how do I remove the dusty/musty smell of old phonograph records and their cardboard album covers? My mother’s photograph records have been stored FOR YEARS in a closet, and then in plastic totes/storage containers. The container has the paper “sleeves” that have turned brown and have crumbled. The other container has phonograph records and cardboard album covers that have been stored in a plastic totes/storage container for about 20 years, and are in better condition, but they smell musty. Help! Thank you.

  7. Alice Carroll says:

    Thanks for also talking about how fogging can be a good option for getting rid of molds. I’d like to find a good odor remediation service because there are still some musty smells in my home. It would be best to get that sorted out before I get sick from it.

  8. Thank you Jennifer for your extensive and informative explanantion. What can be used for the health of individuals exposed to mold i the workplace? Specifically what can I do for my body and health? The workplace will do nothing. I appreciate your feedback.

  9. We moved into a new home, (new to us) a month ago. The garage had a strong odor to it when we opened the door. The house was the previous owners second home with very little use, so the garage was closed up for extended periods of time. I don’t know how to describe the odor; it is a stale musty-ish smell that we believe is coming from the plywood walls. We sprayed the concrete floor with a mixture of bleach and water, then power washed the floor, and sprayed some of the walls with bleach/water mixture as well. I now know after reading your articles that this was a mistake. We opened the doors and a window in the unfinished space above the garage and ran fans for days to get the air circulating. We don’t really see any mold per say, but there may be some small black speckles on the plywood, it is hard to tell. The building has lots of trees around it, and we have left the window open for a month now. The smell remains! Unfortunately, we have moved a lot of belongings into the space above the garage. Help, do you have any recommendations.
    Thank you, Shelly

    1. Hi Shelly! You absolutely want to use some Chlorine Dioxide “mold bombs.” Here is the link to the company I use professional and personally for that: One 50g packet should do the trick here! Have a look at the site and please reach out with any questions!

  10. Thank You for helping me negotiate these problems. Your website saved me from future problems and is excellent at addressing my confusion and frustration.