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Does Fogging Eradicate Mould?

Updated on
February 20, 2024

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Does Fogging Eradicate Mould?

Some say yes, some say no, others haven't the foggiest... (ahem). The truth isn't quite as binary. There's a variety of fogging tecnologies, each with varying levels of efficacy in the eradication of mould. If you forced us, like a reluctant politician on Question Time, into a corner where a 'yes' or 'no' is the only out, we'd probably have to say no. Most fogging technologies don't completely destroy mould. Please note the word: 'most'. That might seem a weird admission for a mould remediation company who use fogging to eradicate mould. Well, hold onto your hats, we'll get into that momentarily.

As per the Housing Health and Safety Rating System, mould is a category 1 health hazard – the same as asbestos. This is a frightening prospect and one that feels somewhat underappreciated in the UK. Once mould has been identified in a home, it needs to be professionally destroyed to safeguard against the whole host of health problems it can cause or exacerbate. Fogging is the industry standard in the eradication of mould. It's important to clarify; there is no silver bullet when it comes to resolving a mould problem. The cause(s) of the mould will vary from house to house and will need to be identified and addressed individually. Very often, part of the process involves the prescription of remedial actions which need to be taken to mitigate against the presence of excess moisture. But, some steps within the wider remediation process can remain the same. Mould eradication is one of these.

Why Fog?

When you pay a professional to come in and resolve a mould problem, you expect them to deliver a service that is beyond your own skill set and expertise. You could buy a fungicidal sterilant and wipe or spray it onto a mouldy surface relatively easily. However, professionals know that 95% of mould is invisible and at the point at which you can see mould on a surface, your property is likely saturated with invisible mould spores; on surfaces, in the air and hidden within and behind walls, floors and furnishings. This sounds dramatic, but consider the following from US-based fellow mould removal experts Mold Busters:

‘Mold begins to grow as soon as its spores land on a damp, fibre-rich material (wood, fabric, drywall…) and it can spread around the house within 24 to 48 hours. It colonizes in one to twelve days and grows at one square inch per day. In less than a week, it can cover surface areas of several square feet.’

A professional, therefore, would look to apply a mould treatment in a systematic and comprehensive way, in order to attain a near-total coverage of your home and it’s constituent parts.

Not all fog is created equal

You’d be forgiven for thinking fogging is fogging – that one professional mould removal expert who uses it is much the same as the next. But the reality is quite different. There is quite a spectrum of fogging techniques, each with their own relative set of strengths and limitations. Let’s take a look at the most common:


Before we turn on the fog, we just wanted to acknowledge the benefits and limitations of the DIY methods at your disposal. A quick Google search, or even intuition, might point you in the direction of that bottle of bleach sitting under your sink. But, if you were mulling that over, we’d urge you to reconsider. Bleach does not destroy mould, it just depigments it. This means that the mould is less or no longer visible but very much still alive; breathing spores and harmful mycotoxins into the airspace. As mould is a living organism which has been refined by natural selection, it has defence mechanisms. When threatened, it spores more aggressively into your airspace. If you spray it with any generic over the counter cleaning product, all you achieve is to aggravate it. Doing so inadvertently makes the problem worse. It increases the number of airborne spores seeking out new places to take root and grow as well as the harmful mycotoxins which attach themselves to them. Doing-it-yourself will probably get rid of the visible mould for a time. But, when it comes back, which it will, it will probably be worse than the first time. Most importantly of all, it also increases the risk to your health posed by the increase of airborne mycotoxins and the horror show of illnesses they cause or exacerbate.

‍ULV Fogging

ULV, or ultra-low volume fogging, is a technique which aerosolises a sterilant in order to apply it evenly. ULV fogging is often deployed via the use of a backpack and handheld nozzle, Ghostbusters style. The sterilant is compartmentalised as a liquid solution and is sent to the nozzle when the trigger is compressed. The ‘fog’, in this case, is created by a built-in motor which forces the air in the nozzle to swirl, creating a high power, low-pressure mist. The fog is typically comprised of comparatively large droplets, ranging from between 5-30 microns in size. The sterilant, as with dry fogging, works by penetrating, immobilising and destroying the mould cells it encounters. The biggest issue with ULV fogging specifically is the size of the particle which it creates. It's problematic for a number of reasons:

  • Mould spores vary in size but typically range from 4 – 20 microns in size. Therefore, the sterilant will not be able to go everywhere mould spores can, meaning not all the mould is going to be destroyed. As long as some mould spores are allowed to survive, there's a chance of reappearance following treatment.
  • Another issue with the larger, wetter droplets ULV creates is that the fog quickly condenses on surfaces. As a result, it doesn't dwell in the air for long before it condenses on a surface. This means the majority of airborne spores and harmful mycotoxins aren't destroyed.

If the majority of airborne mould spores go untouched, then the mould has not been systematically eradicated. The airborne spores will eventually settle on surfaces. The fact you've already had mould tells us, unfortunately, that you have the requisite conditions for it to thrive. The mould will invariably resurface and continue to spread. Crucially, your health is still at risk. Mycotoxins attach themselves to mould spores and when airborne, can be inhaled, posing a significant risk to health. Enough so that the government deem it on the same threat level as asbestos.


It’s not just a gimmicky name or play on words, ozone technology uses the same naturally occurring gas that can be found in the upper levels of Earth’s atmosphere: O3 or trioxygen. It’s as simple as it sounds. The air we breathe, O2, or dioxygen, consists of two oxygen atoms, while ozone fog, O3, contains three. It’s the presence of this third, more loosely connected oxygen atom, that makes ozone an unlikely candidate as a fungicide. The third oxygen atom is prone to detaching from the ozone molecule and reattaching to other molecules, oxidising them in the process. The process of oxidation breaks down microbial membranes, proteins and nucleic acids, essentially eroding the very fabric of living organisms. Hudson and Sharma's study (2009) for the Journal of the International Ozone Association summarised the benefits of ozone technology:

‘Ozone gas has several advantages over alternative liquid treatments; it is easy and cheap to produce from air or oxygen, it diffuses quickly into all parts of a room, including cracks and crevices’.

Sounds great right? Unfortunately, O3 does not discriminate when finding matter to break down through oxidation. In fact, the level of ozone required to systematically and comprehensively destroy mould is extremely toxic to humans. Consider the following from the United States Environmental Protection Agency (EPA), who states:

"(there is) evidence to show that at concentrations that do not exceed public health standards, ozone is not effective at removing many odour-causing chemicals…viruses, bacteria, mould, or other biological pollutants."

In other words, the level at which ozone is effective in comprehensively destroying household mould is also the level at which it would begin to destroy cells in the human body, making it extremely unsafe. The house would have to be empty for days following the treatment. That or the level of ozone is reduced, meaning the mould is not completely eradicated. So, it’s not the easiest method to get right when treating household mould. It’s a fine balance between a likely reoccurrence of the problem or endangering your life.

‍Dry Fogging

Full disclosure: our business uses dry fog, so we’re biased. But with good reason. We believe our assertions are objectively demonstrable by the science. Our dry fog system is the only technology in the UK which eradicates all types of household mould; surface mould, airborne spores and mycotoxins and the hidden mould behind cavity walls, under floorboards and in soft furnishings. What’s more, our microbial film coats all surfaces, preventing it from coming back. Let's take a look at what makes these two technologies in the same family, different:

Our patented dry fogger condenses our sterilant to a smaller molecular size than is possible with ULV technology. This means three things: First, it is unable to condense on surfaces and dwells in the air; eradicating the abundance of mould spores and harmful mycotoxins traditional methods can’t deal with. Second, our dry fog machine creates positive air pressure, meaning the dry fog is forced to fill the entire volume of a room or house, forcing the sterilant to dwell on every surface and object. Third, it can reach every conceivable space within your home including behind cavity walls, meaning we are able to comprehensively eradicate every last trace of mould.

The Verdict

Fogging is only part of the mould remediation process. You can’t just buy a fogger and have at it. Ascertaining the type and cause of damp, and then correcting it, is key. As is safeguarding against future mould growth. Preferably, you can find a professional service which wraps each strand into a single service. But, when it comes to eradicating mould, we believe the science stands with dry fog. It has the micron size to get everywhere mould spores do, it has the ‘dryness’ to dwell in the air long enough to tackle the stubborn airborne spores and mycotoxins and, when coupled with positive air pressure as ours is, it can access the hidden spaces under floors, behind walls and wallpaper and within soft furnishings. Finally, when used in conjunction with a non-toxic sterilant, it is quick, safe and family-friendly, meaning minimal disruption. What better way to sign off, then showing you a microscopic view of mould cells before, during and after a Pure Maintenance treatment.

  1. The Practical Application of Ozone Gas as an Anti-fungal (Anti-mold) Agent. James B. Hudson; Manju Sharma, Viroforce Systems Inc. Laboratory, Vancouver, Canada
  2. Sporangiospore Size Dimorphism Is Linked to Virulence of Mucor circinelloides. Charles H. Li,Maria Cervantes,Deborah J. Springer,Teun Boekhout,Rosa M. Ruiz-Vazquez, Santiago R. Torres-Martinez,Joseph Heitman, Soo Chan Lee Article