Mold and Mildew: What Hydroxyls Actually Do

Mold’s toxins do not stay on the wall

Mold is not only what you can see. Its toxins leave the surface they grew on and enter the air you breathe.

They become airborne. Fungi grown on wallpaper released mycotoxins into the air at air velocities of the kind found in buildings, and some toxins were recovered in particles smaller than 2 µm — small enough to reach deep into the lungs.

Ventilation systems store them and give them back. A review in the Annals of Work Exposure and Health found mycotoxins in HVAC filter extracts, and concluded that HVAC systems can act as a source of accumulation and release.

Water damage changes the scale of the problem. A post-flood study of indoor environments measured airborne concentrations up to 5,720 CFU/m³ and dust at 2.5 × 10⁵ CFU/g — as much as twenty times control locations — with mycotoxin-producing Aspergillus species identified.

This is why a room can pass a visual inspection, and be properly cleaned, and still not be clear.

What hydroxyl radicals do to mycotoxins

Hydroxyl radicals are among the strongest oxidants available, which is why advanced oxidation works on contaminants that resist other treatments.

Aflatoxin B1, a potent, naturally occurring toxic compound and Group 1 human carcinogen produced by molds of the Aspergillus genus, is susceptible to hydroxyl attacks. The 8,9 double bond in the dihydrofuran ring is the reactive point, because the double bond is conjugated with an oxygen atom. Degradation proceeds by cleaving the furofuran ring, then oxidizing further.

Hydroxyl radicals have been shown in studies to drive that degradation directly. 

Hydroxyls have been shown in studies to break these mold toxins apart in food and plasma systems.

And they destroy the molecules that smell of mold fastest of all

The musty, earthy smell of mold comes down to two compounds more than any others: geosmin and 2-methylisoborneol. They have been studied for decades — not by the air-cleaning industry, but by water utilities, because the same two molecules are what make drinking water taste musty.

That research is unusually specific about hydroxyls. Geosmin and 2-MIB react with hydroxyl radicals at rate constants in the range of 10⁹ to 10¹⁰ per molar per second — which is chemistry’s way of saying that nearly every time a hydroxyl radical meets one of these molecules, it destroys it.

Put head to head with sulfate radicals in the same system, hydroxyls did two to three and a half times more of the work. In a separate study pairing different oxidants, hydroxyl was “the most important reactive species”. This is why hydroxyl-based advanced oxidation is standard municipal practice for musty water.

How Hydroxyl Technology Works →

The published research

  • Mycotoxins become airborne, in particles small enough to breathe

    Fungi grown on wallpaper released mycotoxins into moving air at building-like velocities, with some recovered in particles smaller than 2 µm.

    Applied and Environmental Microbiology, 2017 →

  • Ventilation systems accumulate them and release them again

    Mycotoxins detected in HVAC filter extracts, fumonisin B2 most prevalent at 0.6–21.4 ng/g. The review concludes HVAC systems can act as a source of accumulation and release.

    Annals of Work Exposure and Health, 2024 →

  • Water damage raises indoor fungal loads as much as twentyfold

    A post-flood study measured airborne concentrations up to 5,720 CFU/m³ and dust at 2.5 × 10⁵ CFU/g — up to twenty times control locations — with mycotoxin-producing Aspergillus identified.

    Post-flood Aspergillus study →

  • Aflatoxin B1 has a specific site hydroxyl chemistry attacks

    The 8,9 double bond in the dihydrofuran ring is the reactive point, because it is conjugated with an oxygen atom. Degradation cleaves the furofuran ring, then oxidizes further.

    Mycotoxin Research, 2025 →

  • Hydroxyl radicals drive that degradation directly

    Under ultrasound, water splits into hydroxyl radicals, hydrogen radicals and hydrogen peroxide. The hydroxyl and hydrogen radicals drive hydration and hydrogenation of the toxin; the peroxide drives epoxidation. Reaction products identified.

    Degradation pathways of aflatoxin B1 →

  • And the process is dose-dependent

    Oxygen plasma degrades aflatoxins along a dose-response curve: once the surface saturates with hydroxyl groups, continued exposure breaks aromatic ring bonds through to CO and CO₂.

    Measured in food and plasma systems, at doses above those in a treated room — which is why mycotoxins are on our study list, not in our claims.

    Low-temperature degradation of aflatoxins via oxygen plasma →

  • Hydroxyls destroy the musty compounds at near-collision speed

    Geosmin and 2-methylisoborneol react with hydroxyl radicals at 10⁹–10¹⁰ M⁻¹s⁻¹. Head to head, hydroxyl outperformed sulfate radical by 2–3.5×; in a different pairing it was “the most important reactive species”. Water utilities use this chemistry to strip musty taste and odor from drinking water.

    Water Research, 2015 — UV/persulfate →
    Chemosphere, 2018 — UV/chlorine →
    Water Research, 2009 — 254/185 nm →

  • The musty smell is a gas, which is why filters miss it

    Across 23 US homes the dominant microbial volatile organic compounds were the eight-carbon group — 1-octen-3-ol, 2-octen-1-ol, 3-octenone — running higher in basements. Culture work on building materials adds geosmin and 2-methylisoborneol.

    Ryan & Beaucham, Chemosphere, 2012 →

  • Hydroxyls are the atmosphere’s own way of clearing organic gases

    The hydroxyl radical is the main control on the atmosphere’s oxidation capacity, and its reaction with organic gases by hydrogen abstraction is textbook atmospheric chemistry.

    Lelieveld et al., Atmospheric Chemistry and Physics, 2016 →

  • Hydroxyl-generating devices reduce airborne spores

    A photocatalytic air purifier reduced airborne Bacillus subtilis spores by more than 80% within 15 minutes, with complete removal by 90 minutes. Bacterial spores and a photocatalytic unit — the principle, not a WellisAir result.

    Scientific Reports, 2026 →

  • Moisture is the control variable

    EPA guidance: dry water-damaged materials within 24 to 48 hours and in most cases mold will not grow, and keep indoor relative humidity below 60%. No device replaces that step.

    EPA, A Brief Guide to Mold, Moisture and Your Home →

Proven in a Clinic

  • 66.7% fewer airborne molds and yeasts

    A WellisAir WADU-02 ran for five days in a working 10.9 m² dental clinic with normal cleaning continuing. Airborne molds and yeasts fell 66.7% (p = 0.03). Peer-reviewed, and conducted on our own unit in a real occupied room.

    Paños-Crespo et al., Medicina Oral, Patología Oral y Cirugía Bucal →

  • It releases hydroxyls, with no filter and no UV lamp

    A replaceable cartridge reacts inside the unit to release hydroxyl radicals into the room. One cartridge lasts about three months. There is nothing to clean, and nothing that loses capacity as it loads up.

  • 0.006 ppm ozone — one eighth of the legal limit

    Intertek, UL 867 Section 40 (2025), against a 0.050 ppm limit. CARB certified and ETL listed, and designed to run in occupied rooms.

    The full ozone record →

  • Built to run where mold lives

    3.6 watts, under 30 dB, up to 1,000 sq ft per unit. Basements, bathrooms and closets — continuously, with people and pets present.

Continuous Research and Learning

What is established: hydroxyl radicals break down volatile organic compounds, including the compounds that make a room smell musty, and they degrade mycotoxin molecules in laboratory systems.

What has been measured on our unit: one peer-reviewed clinical study, in which airborne molds and yeasts fell 66.7% in a working dentist office over five days. Its authors called for larger controlled studies.

What we are doing about it: we are following that advice. Further studies are being run in South Korea now, and we are coordinating additional testing in the United States, too. We will publish our findings once they are ready.

Where WellisAir fits

WellisAir is one layer, not the whole answer.

The EPA sets out three strategies for indoor air quality, in order: remove the source, improve ventilation, then clean the air. It calls source control “usually the most effective”, and describes air cleaners as supplements to the first two — not replacements for them. We agree, and for mold the order matters more than usual:

  1. Fix the water. Mold grows because something is wet. Until that changes it keeps growing. The EPA advises drying any water-damaged area or item within 24 to 48 hours — in most cases mold will not grow if you do — and keeping indoor humidity below 60%.
  2. Remove what grew. Clean it, or have it removed. The EPA recommends professional remediation for visible mold over about ten square feet, or any mold in an HVAC system. No air treatment device changes that.
  3. Then treat the air and surface. That is our layer. Once the water is fixed, the growth is gone, what remains is what mold left behind, invisible in the air and on surfaces. That is what hydroxyls act on, continuously, while you live in the room.

“We had mold removed from our house last year and were very nervous to move back in. Two weeks with our WellisAir machine and it has given us the comfort we need.”

Mold and mildew questions, answered

Does WellisAir get rid of mold?

No, and nothing you plug in does. Mold grows where there is moisture, so removing it means fixing the water and cleaning or removing what grew. WellisAir works on what mold leaves behind in the air and in surfaces afterwards, as an important part of the overall remediation process.

What does the science actually say about hydroxyls and mold?

Three things, and they build on each other. First, mold’s toxins do not stay on the surface — they aerosolize into particles small enough to breathe, accumulate in ventilation systems, and multiply after water damage. Second, hydroxyl radicals are among the strongest oxidants available, and researchers have mapped the exact site they attack on aflatoxin B1 and the pathway the degradation follows. Third, the two compounds behind the musty smell, geosmin and 2-methylisoborneol, react with hydroxyls close to the diffusion limit — nearly every encounter destroys the molecule, which is why water utilities use the same chemistry on musty drinking water

Will it get rid of the musty smell?

Musty and mildew odors are the most common thing our customers describe, and the smell is a gas, which is why it survives cleaning and passes through filters. Hydroxyls break those molecules apart.

Do hydroxyls remove mycotoxins?

Hydroxyl radicals degrade mycotoxin molecules — the chemistry is well characterized — as shown in studies using  food, liquid or plasma systems. 

Do I still need a dehumidifier?

Yes, if your humidity is high. The EPA recommends keeping indoor relative humidity below 60%. WellisAir does not remove moisture and is not a substitute for a dehumidifier or for fixing a leak.

Can I use it during or after mold remediation?

After. During remediation the area should be contained and handled by the remediation plan. Afterwards is where customers should reach for it, when the work is done and the smell lingers in the surrounding rooms.

Is it safe to run in a bedroom or a child’s room?

It is designed for continuous use in occupied rooms, with no filter and no UV lamp. Ozone output measured 0.006 ppm in Intertek’s 2025 UL 867 test, about one eighth of the legal limit, and it is CARB certified. It runs under 30 dB. As one customer put it: “It’s so quiet I forget it’s there, and the light is soft enough to leave on overnight.”