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Last Updated: , Created: Tuesday, September 5th, 2023


Hydroxyl generators are used heavily in industrial, commercial and institutional buildings including schools and hospitals for sanitizing the air, controlling offensive odours and providing that “fresh air” smell without fragrances.   They are used extensively in flood and fire restoration for cleaning out pollutants and helping to make spaces habitable.  These are not filter machines and not simple germicidal lamps but machines that mimic exactly what the sun does outdoors to keep the air fresh even while nature is constantly composting organic materials with moulds and mushrooms. 

In another article I discuss the pros and cons of a variety of “air sanitation” devices including hydroxyl, some of which I have used myself.  You can link to that article here.

With several years of study and experience I am convinced that the poorly understood hydroxyl is the most effective pollutant eliminator available to homeowners today.  It literally converts complex carbon pollutants called VOCs and their associated odours into water H20 and carbon dioxide CO2 leaving a “fresh air” smell.  It kills mould and renders mould spores biologically inactive.  Nothing added, nothing taken away – everything transformed as nature does outdoors.   

For how to purchase a residential hydroxyl air purifier in Canada, click here.

The hydroxyl process is both simple and complex as it works nature’s magic on a wide variety of pollutants.  Its wide reach is part of why it is poorly understood.  The most common questions I receive are about an “ozone-like” smell and concerns about “intermediates” breakdown associated with the operation of a hydroxyl generating device. 

Let me take a deep dive for a closer look at what is really happening when we use hydroxyl radicals to improve the air quality in a house rather than simply trying to filter out some of the air borne pollutants with expensive HEPA filters or kill a few germs with germicidal lamps.  I an going to concentrate on the air purifiers made by The Pyure Company in Florida which from my research and experience are the best available.



Hydroxyl radicals have no odour, and it is rare that anyone smells actual ozone from a Pyure machine because the levels are so low.  What can give off various “smells” in a heavily contaminated space being treated with hydroxyl is the formation of transient by-products that are formed in the process of breaking down pollutants, including VOCs.  The odour can vary depending on what pollutant is being treated and its concentration.  These by-products are also rapidly decomposed, and the odor should dissipate quickly unless there is a continuing source of new pollutants.  How long does it take?  From a few minutes to a few days – read on. 



Pyure Company devices use specific frequencies and power of UV lamps to cleave ordinary water vapour molecules (H2O) found in household air, forming hydroxyl radicals (OH).  A newly generated hydroxyl radical reacts when it contacts a molecule of VOC, a pollutant in the air, forming a reactive organic peroxy radical (ROO).  The organic peroxy radical can start decomposing, forming organic by-products.  It can also react with other VOCs by a series of chain reactions involving hydrogen atom removal.  The chain reaction process sustains the decomposition of VOCs throughout the treatment space, not just near the UV lamps.  Each ROO radical initiated chain lasts for 12-14 minutes until two radicals combine to stop the process.  This is called the “lifetime” of the radical.  The hydroxyl is consumed in this process and disappears.  The ROO radical is gradually decomposed by further reactions with OH and other peroxy radicals, releasing carbon atoms as CO2.  This process continues as long as the device operates and there are VOC pollutants in the air.  The reactions stop when there is nothing left to clean.

These processes are the same as what occurs outdoors in nature by the action of UV energy generated by the Sun. Hydroxyls are nature’s dominant sanitizing agent and keep our environment safe for humans, plants and animals. Hydroxyl concentrations outdoors are 1-10 million OH/cm3.  Pyure devices target the same, natural levels indoors to ensure both efficacy and safety.  Each OH generates one ROO radical which react so fast that they do not accumulate.  Trace quantities of ozone are also produced by the lamps but remain at very low levels due to natural loss modes.



As this process continues, the “organic oxidants” react with VOCs they come in contact with, causing the VOC to progressively break down into simpler and simpler “intermediate” organic oxidant compounds as they head to an eventual end state of CO2 and water (H2O).  Does this generate too much CO2 in the house?  The normal levels of CO2 molecules in a house are hundreds of times greater than the number of VOC molecules in a polluted house -- ppm (Parts Per Million) levels for CO2 vs ppb (Parts Per Billion) levels for VOC.  Breakdown of VOC adds too little CO2 to ambient levels to measure.  

Some of the “intermediates” of the progressive VOC breakdown process (simplifying stages of VOCs) can have an odor and be mistaken for ozone, but these types of compounds continue to break down rapidly.  This explains why there are sometimes strange and changing smells.  This is common when initial VOC and other contaminant levels are high.  Because the cleaning agents act quickly, these intermediates do not accumulate in concentration.  You may smell them, but controlled studies have demonstrated that they do not accumulate to unsafe levels.  They are further broken down quickly and efficiently to the final state of CO2 and water.  The hydroxyl radicals produced do not cause any irritation themselves.   If the odour or associated irritation does not go away in about a week, then something is feeding new pollution into the room on a continuous basis.



If a room is cluttered, resulting in poor air circulation, or the VOC source is hidden in a poorly ventilated area where the organic oxidants can’t reach that source, then the pollution and its clean-up process will continue to be present for longer periods of time.  Furniture may need to have doors and drawers opened, closets should be open, even things lifted off the floor for air circulation.  If the hydroxyl-initiated process can reach the chemical VOCs, like paint, perfume, solvents, cigarette smoke or even old wood smoke, it will eventually convert the problem chemicals to CO2.   Then, continuous use of the hydroxyl generator will keep things in check without concentrations of “intermediates” – but simply with clean air.  Hydroxyl without any pollutants turns back into water (H2O).



Ozone is often used for odour removal in fire and flood restoration, but ozone requires high concentrations to remove odours and extremely high levels to have any biological effect, presenting safety problems because ozone is toxic at these levels and highly corrosive.

The natural hydroxyl process eliminates odours without any safety problems for plants, pets or humans or damage to household materials.  In addition to VOCs, it neutralizes light mould and mould spores quickly.  The Pyure Company’s US web site discusses the research done related to microbes and viruses.  All of that is done at levels of hydroxyl found normally outdoors, and with no corrosion at all. 

Biological mould is a very different pollutant than chemical VOCs.  Hydroxyl treatment will kill live mould if properly exposed, but it does not remove dead mould so if you have thick mould, it must be scrapped off to allow the oxidants to get to the underlying mould.  If there is thick mould inside the walls, the walls will have to be opened up and a total mould clean-up and removal may be necessary.  Using hydroxyl after the mechanical clean-up is done, will kill mould you could not reach in cracks and corners. We have always been told that mould is not really the problem for sensitive individuals, but it is the mould spores that cause problems, and spores are released from mould whether it is live or dead.  The good news is that the hydroxyl organic oxidant cleaning process destroys reactive groups on mould spores, degrading spores from both live and dead mould, making them biologically inactive.  Continuous use of hydroxyls can help to prevent mould from growing again from residual spores that could otherwise seed new growth.  Of course, even then, excessive household moisture and condensation must be avoided.



Understanding the hydroxyl process can help you to understand that a changing bothersome odour is a sign that the system is working, and if the odours persist for more than a week or two, that is a sign that you need to look for a hidden pollution source.   When the odour goes away, the odourless hydroxyls continue to take on any new pollutants.  If the odour comes back, that is an indication of the presence of a new source of pollutants that is now being treated. 


Want to get more technical with the science?

For those who want a deep scientific explanation of the “Mechanism of Action” of Pyure hydroxyl generators, it can be found on this page of Pyure’s US website: .




Pyure hydroxyl devices can decontaminate most living spaces, making them habitable for persons afflicted with MCS.  If running a hydroxyl generator causes irritation for you, as discussed above, it would be advisable to treat the process as a household detox. 

Run the machine without your presence and with good air circulation, using indoor fans if necessary, for three to five days – in extreme cases, for a week or two. Less sensitive friends can come in and out of the house for you without problems, even live there as house sitters.  You could even exchange dwellings with them for the time of the detox.  You can visit regularly to test the changes in the air quality for yourself.  If you cannot move out for the detox, run the machine for 8 hours a day, preferably while you are out.  This takes much longer to be effective but can attain the same results with less irritation during the process because each 8-hour period removes more of the pollution source. 

Once the house has been sanitized and you feel you can move back in, some people choose to run the machine less frequently just to continue the process on any pollution that naturally comes into the house with coming and going.  The key with owning a hydroxyl machine is that once you have detoxed the house, you can be proactive and keep any indoor air quality problems under control yourself, like the surprise visit of someone wearing perfume, or a new piece of furniture. Without serious sources of pollutants, few people are bothered by the lighter maintenance cleaning process. 


Buying Pyure’s hydroxly air purifiers in Canada

Large devices for commercial and institutional use are made in the USA and sold and installed through dealers scattered across Canada and around the world.  For now, this is Pyure’s primary market focus. Find a dealer here.

For the story on what I managed to arrange with Pyure to make the residential units available in Canada, check out this link: Hydroxyl air purifiers for residential use in Canada




Two In-Duct Pyure units (IDS™ and IDU™) are certified safe in Canada for continuous use as they have passed the ozone certification test: CSA C22.2 No. 187:20, Section 7.5/7.6.  These are the appropriate units to instal inside heating or ventilation ducts for continuous residential, commercial or institutional use.

One Pyure portable unit, the MDU/Rx™ device, is registered with the US FDA as a class II medical device appropriate for hospital use, but it is not certified as a medical device in Canada.    

The portable units are primarily used in remediation, where rooms are generally unoccupied.  They are a good solution if you want to assess the impact of hydroxyl treatment prior to investing in an induct unit.  Small portable units such as the Mini™ can be used continuously in an occupied space by following the recommendations for an appropriately sized room as outlined in the product manual.  Getting the right sized device for your space is all about maintaining hydroxyl levels at levels naturally found outdoors.

All models use the same basic hydroxyl technology.


Keywords: Carpet, Humidity, Mold, Mould, Flood, Relative Humidity, Air Quality, Ozone, Air Flow, Fire, Cleaning, Restoration, Smoke, Air Changer, Hydroxyl, Air Filters, Odours, Health, Pollution, Smell, VOC, Ventilation

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