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Does Bleach Kill Mould?

Uncategorized Feb 07, 2020

This week we’re talking about disinfectants and more specifically bleach or sodium hypochlorite. “Does it work, no it doesn’t, look it just feeds the mould, no it doesn’t, yes it does, it makes the mycotoxins worse and simply changes mould from one colour to no colour” Fact or fiction?

We all know, there's a lot of websites that say conflicting things. Who do you believe? You might even know the answer, maybe you’ve already made up your mind? But wait - what does the science say?

To bring some perspective to the bleach debate, I’m going to take a look at what the National Wrestling Coach Association has to say. Up to 20% of wrestling injuries are caused by skin infections. Tune in to this episode and find out what the martial artists discovered about bacterial transmission and how this leads to improved disinfection methods and best practice for surface decontamination? HINT: contact sports are associated with an increased risk of skin infections, but the conclusions from their research are valuable (and transferrable) to the indoor living environment and similarly, to water-damaged interiors.

Join me tomorrow as I go through this very practical topic since all of us from time to time need to clean up the mould. After all, over 70% of homes test positive for mould and research shows that windowsills are often the most frequently contaminated sites. What are we to do? Reach for the latest kill mould solution from the supermarket or hardware store, reach for the latest ultra-green plant-based carbon credit contributing liquid or test out something simple like vinegar? Which disinfectants are best for porous and non-porous materials? What about essential oils? TEASER ALERT: Clove oil (a hidden secret)...see the graph showing its antibacterial effect.

All these are viable options you might consider when you need to clean the mould away. But, before you begin, I want to shine a spotlight on what the research says so you can make better-informed decisions for your next cleaning task. Stay till the end and I’ll also show you a simple bathroom hack for cleaning grout joints that have gone mouldy?


Rogawansamy, S., Gaskin, S., Taylor, M. And Pisaniello, D. (2015). An evaluation of anti fungal agents for the treatment of fungal contamination in indoor air environments. Int. J. Environ. Res. Public Health. 12.

Reynolds, K.A., Boone, S., Bright, K.R. and grebe, C.P. (2012). Occurrence of household mould and efficacy of sodium hypochlorite disinfectant. Journal of Occupational and Environmental Hygiene. 9: 663-669.

Schroeder, T., Gaskin, S., Ross, K. And Whiley, H. (2018). Antifungal activity of essential oils against fungi isolated from air. International Journal of Occupational and Environmental Health. 23(3): 181-186.

Young, L.M., Motz, V., Market. E.R., Young, S.C. and Beaschler, R.E. (2017). Recommendations for best practices to reduce the spread of infection via wrestling mats. Journal of Athletic Training. 52(2): 82-88.

Kalkanci, A., Eli, M., Fouad, A.A., Yesilyurt, E. And Khalil, I.J. (2015). Assessment of susceptibility of mould isolates towards biocides. Journal of Mycologier Medical. 25: 280-286.

Slaughter, R.J., Watts, M., Vale, A., Grieve, J.R. and Schep, L.J. (2019). The clinical toxicology of sodium hypochlorite. Clinical Toxicology. 57(5):303-311.



Hello and welcome to this week's live stream. My name is Dr. Cameron Jones and I've got a very exciting episode today. We are talking about bleach or sodium hypochlorite, and this is a bit of a controversial topic because I'm well aware that there are a lot of websites out there that say no, you must never use bleach, especially for mould cleanup, and yet, there are other websites that say the exact opposite. So I want to review some of the science underpinning a lot of these claims. I'm also going to be talking about why bleach works, what its oxidizing ability is. We're also going to be highlighting vinegar and some information on essential oils. So really, this live stream is all about surface disinfection, and we're going to be reviewing some of the important information underpinning all of this.

Now, when I was deciding what to talk about this week, I thought I should of course have a look on PubMed because PubMed's really my best friend, and I found this fantastic paper that was all about the relationship between cleaning of martial arts mats. And as you can see up on screen, this whole area of sport, there's a lot of body contact with mats, and there's interestingly quite a bit of research out there on the relationship between skin contact and these sports mats. And we're going to be going into this in some detail, and I'm going to really talk about what these researchers found, and it's not just from one paper, but I've put all the references up online so you'll be able to retrieve those. And I'd certainly encourage you to have a look at some of these really interesting papers that focus on the different types of cleaning methods and the different chemistries that have been used.

But I'm going to come back to the sports research shortly. Now, what about all of the blogs and news articles out there that say never use bleach to clean mould? Is this another example of real versus fake news? Is it in fact, fact or fiction? Because I can find any number of websites that strongly state do not use bleach. All it does is strip out the color from the fungus and leaves it there or feeds the fungus with water. All of these claims have some partial validity, and I again want to highlight what is true and what is not necessarily backed up with evidence today. And I'm going to move into this now.

So what are we talking about with normal household bleach? Well, the chemical formula and its name is sodium hypochlorite and sodium hypochlorite was developed by a French chemist. It's been used and commercialized now for really since the late 1700s. Certainly in France as of today, it's named after the location where it was first developed and discovered. And it works because it bleaches or oxidizes materials. And what this means is that from an energy perspective, it has the ability to use the electrons and carry out chemical work. And so this is the ability of bleaching out color. And originally, it was used in laundry applications and for textile fiber dyeing. And of course certainly in the paper and pulp manufacturing industries, bleach is used a lot in turning our papers white and even for textiles because cotton fibers are actually not white. They're yellow. So bleach is used routinely in industry all the time.

Now let's get back to the sports paper because I thought that this was just a beautiful example of an applied science problem and it's from a paper which came out in 2017, and what these scientists did is that they were looking at the effectiveness and best practice guidelines for minimizing the spread of skin infections via wrestling mats. And so what they did is that they got over 200 college wrestling wrestlers along with some officials and they did an extensive set of swabs of not only the mats but the hands and feet of the wrestlers before, during and after their fights. And they were looking at the effectiveness of surface disinfection of the mats to see whether they could reduce the transmission of these skin infections, because there's been some great research showing that these direct infections caused by skin micro flora are really responsible for the major injuries that wrestlers encounter and I find that found that really staggering actually as a statistic.

So why I have highlighted or put up this particular graph is to focus on a couple of things because obviously, the researchers were exploring whether or not different types of disinfectants to see how effective they were for cleaning these mats. And so they were looking at various different claims made by different manufacturers, and I have highlighted the 10% bleach solution and bear in mind also that 10% is quite a concentrated form of sodium hypochlorite. But the key takeaway in this particular graph is that within the first two minutes, you have quite a significant reduction in the number of microorganisms which are appearing on this mat. And so if you look at the legend in the graph, you can see that the colony forming units, colony forming units essentially are a little bit like this Petri plate that I'm showing up. And it is the number of microorganisms that really you can count on a Petri plate. And so for this one, for counting up the colony forming units, I just have to make a physical count of the number of fungal cells I see down on that particular plate.

And so when they do this sort of experiment on these wrestling mats and also other researchers have done further studies on tatami mats, which are the Japanese version. And essentially, they discovered that bleach was highly effective in reducing the microorganisms which they were looking at and reducing the overall colony forming unit count. And you can see something interesting, which is an issue that most surface disinfectants have in that they don't kill all of the cells that they come into contact with, but they greatly impact and reduce the total population numbers. And I'm going to talk about some more effects and figures soon because you'll be hearing about something called log-5 and log-10 kill. And we'll be talking about what those numbers mean. And usually, the assumption is that you start off with 1 million microorganisms and you see what the reduction is or what the percentage reduction is. And you'll often see these numbers actually printed on the labels of disinfectants.

But you can see in this graph that you immediately have a reduction in the overall number of colony forming units on the treated or disinfected surfaces. And yet over time, the population of microorganisms then essentially regrows. So really, it's a battle against biology that surface disinfectants will never really solve, but it can certainly be important when you're attempting to clean effectively.

Now if we move on to other graphs within this paper, you can see that they compared the ability of different disinfectants to carry out chemical work or disinfect the wrestling mats. And the most effective disinfectant was in fact an alcohol based disinfectant. But the second most effective disinfectant was sodium hypochlorite or bleach. And there are a range of other trade proprietary formulations which had decreasing ability to get rid of these nasty bacteria.

And again, everything you read and these graphs, although they relate to bacteria, this inflammation is transferable to fungi as well. And then I'm going to show you some specific information from the literature showing the ability of bleach and vinegar and a range of other essential oils to decontaminate those surfaces, more or less depending on what the data shows. Now if we look at some of the other publications, including this really interesting paper from 2012 in the Journal of Occupational and Environmental Hygiene, they published some best practices for using sodium hypochlorite as a surface disinfectant. And initially what they do in their review paper is they discovered that really nearly 73% of surfaces that are randomly tested in any one house, not just those that are water damaged, are going to show recoverable levels of mould.

So make no mistake, mould and bacteria and yeast, they're a normal part of our homes. But certainly, people who watch these live streams each week usually are interested in those situations where there is an abnormal or an abundance of these microflora in the homes. So what the researchers in the paper from 2012 showed was that the more contaminated areas of a home usually are those horizontal services like window sills and the tops of doorframes, where things settle out from the air, and that the most common microorganism or fungal genera discovered in homes is the genus Cladosporium at 31%.

Now, a five minute exposure to bleach or sodium hypochlorite results in a greater than 3 to greater than a 6-log reduction in the amounts of culturable mould. And this is a really important statistic, so you might recall that I said we start off with 1 million different cells, 1 million mould cells, and if we apply the bleach to this and achieve a 10 to the 6 kill, that is going to reduce the population to one or a 99.9999% reduction.

Now this is really, really important because bleach has been shown to be effective on of course, as we know, non porous materials such as ceramic tile and glass. But what about those more porous materials? And there is good research out there to show as well that bleach can be used to some extent on these porous materials. Think about it. Bleach is used to change the color of your t-shirt, like my white t-shirt here, and similarly, bleach will degrade and get rid of... is suitable for porous materials and is also often a component of hair dyes along with hydrogen peroxide.

Now, the interesting information here is that obviously, we know that all homes have some level of mould and a lower percentage of sodium hypochlorite even at just under 2.5% is very effective for reducing the overall levels of culturable fungi in the air and on surfaces and this has a flow on effect to reducing the allergen potential of these microorganisms as well. Now a lot of you are probably thinking, "Well that's great. I never use sodium hypochlorite or bleach. I hate this stuff. I would never even consider using it and I like organic compounds such as vinegar."

And so that brings me onto the next controversial component of today's live stream, posing the question, "Does vinegar work?", and I've asked myself this as well, I've looked in the literature. Does it work? Maybe? Yes? No? What do you think? Well, it's an acid. So acids have chemical energy as we know from pH or the power of hydrogen. The further along the pH scale you are in either direction, they have greater ability to carry out chemical work and dissipate their chemical energy. And so whether you're alkaline or acid, the more acid or alkaline you are, the greater the ability to do useful work, and that is the fundamental tenet and premise of chemistry.

But let's move to what the research says again, and if I move on to a great publication that came out in the Journal of Occupational and Environmental Health in, let's see, in 2017, they published an excellent piece of research looking at the reduction in the zone of inhibition for these fungi when various different substances have been used to get rid of five target fungal microorganisms, including penicillium and aspergillus. And importantly, they've looked at the relationship between the ability of these different chemistries to get rid of penicillia that have colonized inside the home versus those that are available and growing outside. Because often in water damaged buildings, there will be selection pressure often due to the high amount of moisture content and water activity present in water damaged building materials and you will get overgrowth of particular clusters or taxa of fungi. And over time, these can colonize and be somewhat different to the wild type penicillia outdoors.

So this is a very interesting paper because it has drilled into this fine detail about the difference between outdoor and indoor moulds. And lo and behold, we can find that the zone of inhibition or whether or not water kills fungi. You can see that the scientists recovered no zones of inhibition, meaning that water didn't reduce the ability of these fungi to grow at all. Now what happens when we move to bleach? And this is looking at 3.3% sodium hypochlorite in solution. So it is in the wet phase and they discovered that you can get rid of... and what these graphs are showing is that they're bar graphs and the legend down the bottom explains this, and this shading of the bars relates to whether the zone of inhibition that they measure was done on between day two and three, between days four to five or at day seven.

So if you look just for example, at the longterm decay or the ability of the disinfectant to cause a longer term reduction in the total number of fungi, we can see that bleach is very effective. And if you look at the scale of the axis, you can see it goes from zero to 40. The total size of inhibition was only 35 millimeters because that was the size of the Petri plates that the scientists used, and the zone of inhibition measured readily outwards in that circle went to approximately 35 millimeters according to their materials and methods. And the interesting thing here is that bleach is very, very effective against a whole range of different moulds. And you can also see that for Aspergillus for example, at day two to three and four to five, there was no regrowth. So that's really important.

Now what about vinegar? Because people love vinegar, it's not very effective. You can see that the zone of inhibition only worked for this fungus called Coprinellus, and there was no reduction in growth rate for the indoor or outdoor penicillium or for Aspergillus or for Ulocladium, which produces quite significant allergen spores. So I think you should dwell on the impact of that slide when you instantly potentially in your mind, think, "I'm going to use vinegar on my mould contaminated surfaces because I know it works, because I read about it online." Well, I'm here to tell you that the research says that vinegar is not particularly effective and there is lots and lots of additional research that I have and I've put in the references to this live stream confirming this fact.

Now what about essential oils? Because there's another group of people who love the concept of using natural essential oils because A, they smell nice, B, they're organic, C, they're green, they're friendly, they give you a nice feeling often due to their odor. All of these are really sensible and legitimate reasons for choosing one type of chemistry over another because at the end of the day, usually you need to do some manual work and use some sort of scrubbing action to get rid of mould. And really, the purpose of today's talk is not to say you ought to always use bleach to remediate your severely water damaged building, but this type of research does strongly support the position that for small areas of mould contamination, that you can use disinfectants and they should be bleach based or even essential oil based and maybe stay away from simple elbow grease with water or vinegar.

Now clove oil treatment, I'm going to make this whole live stream actually on the importance of essential oils but I just want to highlight on what the results show for clove oil and you can see that it is highly effective at creating really huge reductions that is not seeing many of these fungi appearing on the Petri plate over time.

And that's really all I wanted to say about clove oil. Yes, it definitely does work and there is great evidence out there to support its use. Now if you don't believe me and want to see something a little bit clear and not in the graph based format, I've put up this Petri plate here to actually show what a zone of inhibition looks like. And in all of this research, especially if you drill into the references I've put at the end, you'll read about something called minimum inhibitory concentration, and basically they usually use a disc in which they impregnate the various different disinfectants, be it sodium hypochlorite or vinegar or water or clove oil or eucalyptus oil or limonene or cinnamon oil or a range of different products. And they're looking for a reduction in the size of the colonies that are able to grow in that environment, which has this disinfectant, and this is what the researchers would see in the lab when they're doing this sort of experiment and you will be able to see a halo or a zone of inhibition, meaning that there is no growth into the area closest to the disinfectant.

That's a really important point to emphasize and keep in the back of your mind because that's what you're doing when you use any of these substances in your home. Now I'm going to insert a viral internet cleaning hack here and what I mean by that is that I discovered this by chance again online earlier this week and I wanted to play it to you and I'm going to do that now.

Okay. I came upon this really interesting news story a couple of days ago and I get calls about this all the time. People ask me, does bleach work? I've read online that bleach should not be used with mould. [inaudible 00:22:52] Well [inaudible 00:22:55] is that in some situations, bleach is very effective and this new story really demonstrates this unequivocally. So what happened is that a British woman was able to clean the mould deposits in her bathroom. She shared the before and after results onto a Facebook group and the response really was overwhelming. Now the Facebook group was called Cleaning Tips and Tricks, and it got a lot of praise from other cleaning fans who were desperate to try as the journalist says this hack for themselves. Now look at the before and after results. Now that's the typical scenario that many of us find ourselves in over time because it's such a warm, humid and wet environment.

A lot of the porous grout lines become mouldy, and this happens just as a natural phenomena within the house, and yet there's a whole industry behind the cleaning products you use to get rid of this, but a lot of us have tried things like this before and found that spraying the grout lines with bleach or any of the products that are on the market for removal of mould. Sometimes it works, sometimes it doesn't. And so this particular hack that this woman posted about, she discovered that if she actually applied cotton ball or tissue paper or even toilet paper to the grout lines and she'd spray it on the bleach beforehand, she got really good results and so basically, she's saying spray the bleach on, leave the cotton balls or toilet paper on it and let it sit for 12 hours or even overnight. And so the results as you can see from other people that she shared this with was really overwhelming. And so a lot of other people have found good success with this as well.

And so I just really wanted to bring this to your attention, and I'm going to be going through some of the science behind why bleach does or does not work very shortly. Anyway, I think it's a really good before and after set of results and I wanted to share it with you.

Yeah. Okay. Well I have shared it with you and you can see that that lady found some success in using this. Now, I'm not suggesting that this is a panacea for all indoor air quality or mould problems because it's not, but the point of today is to emphasize that bleach has a bit of a bad name, certainly with its connection to the mould remediation industry, but I need to put a couple of caveats on this because bleach is a dangerous chemical if it is mishandled, and mixing vinegar and bleach together is a very bad idea because it will release toxic chlorine gas.

So we need to be very mindful of this and definitely do not do this and do not mix these two chemicals together. Now there are a range of other risks as well and bleach works because it is toxic. It does have a strong oxidizing capacity and it does have a pH which makes it a strong oxidizer, and it is therefore corrosive and will be damaging to mucus membranes like your eyes and nose and mouth and tongue and that sort of thing. Furthermore, you should be aware that dentists use sodium hypochlorite to routinely clean out root canals, and that is the extracted pocket of the tooth. However, even dentists are strongly aware of when to not use sodium hypochlorite because it can damage delicate tissue adjoining the extracted tooth. Prolonged and extensive exposure from your skin to bleach will cause a hypersensitivity reaction and it can in some cases cause chemical burns to the affected skin and of course inhaling the fumes of bleach.

It's quite noxious so you're going to probably move away. If you are working with bleach in any type of enclosed environment, that's a really bad idea. Certainly people who are using bleach to clean in their bathrooms must make sure that windows and doors are all open because these chemicals release a lot of vapor and this vapor is a strong irritant. However, the medical literature does report that it is usually a mild irritation of the upper airways and is not going to cause any longterm damage unless you are exposed to high concentrations for long periods of time.

Importantly, it will damage your eyes, and there are a number of reports of corneal injuries, but again this type of symptom generally reduces in severity after one to two days. But bear in mind that high concentrations of bleach can be very, very damaging to you. So I think that that is something that all of you should be aware of and the conclusions that I want to move towards, again from another paper that I'm citing in the references at the bottom of this livestream and essentially, because we do need some conclusions to wrap this up in some direction forward and essentially a less than 10% solution of bleach, in fact a 2.4% solution, which is commonly found in a number of products that are available commercially, has been tested against a range of water damage fungi. In fact, many of the most common water damage fungi such as penicillium, Stachybotrys infamous black mould, Alternaria, Aspergillus niger, which are potent spore producers and Cladosporium, and they have been able to inactivate stock cultures to undetectable levels after five minutes of contact time on non-porous surfaces like the bathroom tiles and after 10 minutes contact time on poorest surfaces.

So the take home message here is it is the dwell time, like that first graph I showed you about the wrestling mats. Over time, the population of microorganisms does tend to grow through the disinfectant, but for these porous and non-porous surfaces, it is the contact time which is the all important variable here as well as the concentration of the underlying chemistry. And the home message here is that sodium hypochlorite based disinfectants are in fact highly capable of reducing the growth of fungi and therefore reducing the number of allergens present in the indoor environment.

I've covered some very important but controversial issues here today and I urge you to drill into the references to see for yourself what other scientists have to say about the disinfectant ability of sodium hypochlorite, bleach and other essential oils, and then make your own conclusions about which products you do or don't want to use. In any case, my name is Dr. Cameron Jones. Next week, we're going to be focusing on a very interesting and practical cleaning method that looks at another type of a disinfectant and infect sterilant that does not rely on any form of chemistry. So that's the teaser I'm going to leave you with. In any case, have a great week and bye for now.



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