Thanks for joining me for this week on The Mold Show. And today we're going to be talking about foot fungus. We're also going to be talking about the microbes that colonize our shoes and socks. I also want to talk a little bit about the best practices for hygiene around the home. The reason I wanted to do this episode is that the media here in Australia has interviewed me over the last couple of weeks, both on radio and on TV about this topic. And I can only imagine that this is because the number of people worldwide who have treatable skin infections is in the order of one to 2 billion people. And superficial fungal infections, are extremely common and they've got a worldwide prevalence of between 20 to 25%. That means one in four people have potentially got a fungal foot infection at any point in time.
Now I stress these usually are not life-threatening, but it is a significant practical problem. Most of us have probably experienced athletes foot and the fungi that are responsible for this include Trichophyton and Tinea, and these fungi are very contagious. Lots of research into the washing of textiles has found that even after washing cloth at 40 degrees Celsius, sometimes recovery of these germs is up to 40%. Whereas if you increase the wash temperature to 60 degrees Celsius, recovery drops to 6%, but 6% is still a significant percentage. And I want to talk to you a little bit about clothing in general, and about best practices, because this is a significant practical problem. And in fact, the US Army has also done research into foot fungus and other skin infections that affect moist, warm areas of the body. And their modelling showed that with lost time and healthcare costs that the army was spending $1 billion over a five year period.
So when you look at it from the viewpoint of a sock, a shoe essentially is a hostile environment and that's because it's moist, warm and humid. So my recommendation for socks is to wear them once and then wash them because these foot fungi and the infections they cause affect both the healthy and the immunocompromised. When we look into the literature, the earliest paper I could find on PubMed dated back to 1924, and this too was talking about infected shoes and the pathogenic microorganisms found inside shoes and being transferred onto feet. And even back then the recommendation was to change socks daily or add compounds that would reduce the microflora growing on these surfaces. So back in the 1920s, they were suggesting that people add zinc oxide powder. And that zinc oxide powder exerts an antimicrobial effect. Now, if we fast forward to now, we have a range of different sanitization methods to deal with foot fungi.
And of course, this includes laundering socks, and sometimes even shoes like runners at high temperatures. Now, remember I sent 60 degrees Celsius? This is really important, but other practical steps include drying washed clothing and even footwear in the sun, so it's exposed to the correct wavelengths of ultraviolet light because this is germicidal to microorganisms. And of course, there are newer developments in textiles and these are called therapeutic clothing or therapeutic textiles. And just like that 1924 paper talking about zinc oxide, newer fabrics are often impregnated with copper oxide, and this is a really good development. And I'm really interested in this.
So to recap, the most common foot fungus is Trichophyton and that is responsible for nail, hair, follicle and other superficial skin infections. These are often all classed as dermatophytes and these fungi require keratin for growth. And of course, keratin is found in the hair, skin and nails. Now, while you are visualizing probably your own socks and shoes and runners, we mustn't forget other footwear items at home like slippers. And why I wanted to mention slippers is these can act as fungal reservoirs and especially because many people keep their slippers for long periods of time before they're replaced, slippers also have been shown to be heavily contaminated with fungi.
So other things that I want to talk to you about is smells. So one of the questions I was asked is, "Can we use smell as a way of detecting the presence or absence of germs on our clothing?" Well, in a sense we can, but the key term here is using our senses to detect an odour. And what is that odour? That's the generation of microbial volatile organic compounds, mVOC's. And that means that something is growing on these moist, warm areas of the body and in turn being transferred to the item of clothing.
So I would much prefer people make behavioural changes to their washing and hygiene methods that they use around the house, such as increasing the ability for water to evaporate, improve ventilation around the home, decrease humidity, and even consider introducing a heated towel rail, because the thicker the towel, the longer it's going to take for water to evaporate from it and the greater the probability that germs will form on the towel.
And if we, again, dive into the research literature for towels, the best practice is to launder and wash that towel out after the three uses, especially if you can't adequately dry it out. But what about sheets? They should be washed weekly. Pillowcases at least three times per year. Sorry, I make an error, pillowcases should be laundered weekly and pillows should be washed three times per year or replaced. So the key take-home message here is that washing frequency needs to be improved. And really this is a bit of a no-brainer, because like with shoes and socks being a hostile environment, humans shed 500 million skin cells throughout the day. So this combination of skin cells and sweat and moisture being present on bedsheets can definitely contribute to unwanted bacterial, fungal, and yeast growth, which could be potentially transferred onto us.
And again, we're always concerned about this issue of fomite transfer and fomite transfer, certainly for hospital-acquired infections (HIA's) is the situation where your hands come into contact with a contaminated item of clothing, and then you touch your face, nose, eyes, or mouth, and you transfer those germs. And again, the research literature states that these types of fomite transfer events is very successful. And in one-third of cases, transferring from fingers to these organs of the face occurs at about a 33% success rate.
So we need to be mindful of that as well. So people definitely need to improve their washing habits. And the best way to do that is to reduce indoor humidity, improve indoor airflow and reduce the moisture content. With regard to delicates like underwear and briefs, there really are no hard and fast rules here. There's certainly a lot of internet chatter about replacing underpants and briefs every six months, but it really does depend on the cleaning frequency and whether or not the material that goes into constructing those garments can stand up to repeated washings without losing functionality.
And really, what do we mean about functionality? The structural integrity of an undergarment? Well, you're really looking at the weakest link, which is often the elastic. And it does then depend on the different types of materials that these briefs may be constructed from. So cotton, the dominant fibre, is cellulose. For wool garments the dominant fibre and material is keratin. Where for silk it's fibroin and polyester, well, this is a human-made material based on PET and each of these different fibres obviously have greater or lesser natural antimicrobial properties to them, but also the type of fibre dictates how thick or coarse it is. And obviously, this impacts then on the weave of the fabric and then how easy it is to dislodge dirt and material and germs which grow on these surfaces. So it really is a combination of the amount of moisture that came into contact with the garment, how dense the fibres are, and what those fibres are made from.
And we have to put this in perspective as well, that human beings only started wearing clothing about 150,000 years ago. The earliest textile fibres date back to about 35,000 years. And if we look at the fossil record for shoes, they definitely do date back to approximately the stone age where fossil remains have been recovered showing that early shoes were often made and constructed of deerskin, and socks were made out of straw. And this dates back to 3,300 years ago.
So remember, once your socks or underpants lose their structural integrity, then it might be time for you to use them for shoe polishing or car washing, but there is no hard and fast rule when they have to be thrown away. However, I do need to tell you a little bit about what some of the research does talk about with regard to female long-distance runners who often experience unwanted incontinence and the research literature suggests that these runs can be as short as a three-kilometre run.
Now, whilst raising the issue of incontinence may be a little bit, not the best visual picture. I want to talk about it because it does impact on different types of moisture, apart from sweat, which can contaminate undergarments. And remember why it's important then to wash these after every workout. Because those undergarments, if they're placed in the laundry hamper, also increase the local humidity in there. So one should be very mindful not to let clothes pile up in the laundry hamper either. And typical microbes, which grow in briefs, of course, include Candida. And these are linked to urinary tract infections, as well as the obvious fecal coliforms.
With regards to bedsheets, as I said, they need to be washed weekly. There is good research evidence showing that illnesses and fevers obviously are going to impact on the moisture content transferred to these textiles and excellent research carried out by Australia's CSIRO with regard to coronavirus, showed that the viability of this particular virus on cotton is temperature-dependent. And recovery of the SARS-CoV-2 virus at 20 degrees Celsius ambient temperature was up to two weeks. Whereas increasing the temperature to 30 degrees Celsius reduces the recovery of viable virus to three days.
So in all cases, we want to reduce the moisture content, increase the temperature and do practical things like after clothes have been washed, put them in the tumble dryer. And if you don't want to put them in the tumble dryer, put them outside on the line, because even with hospital washed textiles studies have also shown that these easily become contaminated before the first patient has even gotten into the bed.
With regard to towels, well, I mentioned at the beginning of this podcast, that we must dry out thick towels. We must always wash them after every few uses and we shouldn't leave them in the laundry hamper or basket since this contributes to cross-contamination. With regard to what setting you should use on your washing machine, I always recommend washing at a hot cycle for longer. That is, at least 60 degrees Celsius, and to use an activated bleach detergent. Often these will say on the label it contains sodium percarbonate. This is really important because this, again, has been shown in the literature that activated oxygen bleach detergents are superior to other detergents at removing and also sanitizing the garment or textile.
One last thing I want to mention about coronavirus, certainly because all of us are mindful of the potential for anyone to become ill and then spend time in bed. That coronavirus shedding can occur for up to two months after symptom onset. Therefore, this is another reason not to share towels and to regularly wash bedsheets. And obviously, placing a wet towel back into the hamper for days will naturally cross-contaminate other items of clothing and make the whole wash more important to make sure that germ reduction occurs.
Now, what are some of the dangers from germs building up on textiles? Well, I already mentioned the 33% effectiveness of fomite transmission from an object to your eyes, nose, and mouth, but we have to list some of the others. And common infections of the skin include staphylococcus skin infections. Staphylococcus aureus is a well-known germ and this bacterium commonly can lead to abscesses and other skin infections. Candida albicans is perhaps the best-known yeast, and this is responsible for urinary tract infections. Trichophyton causes athletes foot, and another microbe called Clostridium difficile can cause diarrhea-like symptoms and infect the colon.
Again, E. Coli, perhaps the most well-known bacterium commonly affects the skin and leads to urinary tract infections. Other microbes can cause blood infections and even pneumonia such as Pseudomonas. And of course, fungi can cause direct infections, allergy and even endocarditis. So beware of recurrent skin infections and perhaps look at the potential of your bed line or bathroom towels and soft furnishings like this around the house to be potentially contributing to recurrent skin infections. Obviously immunocompromised people who suffer from diabetes or increased blood pressure or have underlying diseases or are obese are at increasing risk from hospital-acquired infections and cross-contamination from germs being present on textiles.
Now, let's just go through what we know about washing machines. A really elegant study looked at the microbiome, or the microbiome, of germs around the built environment in the house. And the scientists looked at 70 different washing machines and they found that 80% of these were positive for common and rarer fungi. What do I mean by the rarer fungi? Well, these are often described as thermotolerant fungi and these live in the seals of washing machines and dishwashers. And often these are found to be colonized with black yeasts. And what are the most contaminated areas of the washing machine? Well, again, the research shows that it's the detergent draw and the sump and that front-loaders are far more likely to be contaminated rather than top loaders.
So how are you going to clean your washing machine? You should consider running a full cycle without clothing through your washing machine, perhaps adding some liquid chlorine bleach, or even vinegar, and wiping around the seals. Or of course, any hospital-grade disinfectant, liquid disinfectant of your choice. So it's important to do this with your washing machine. And again, as I mentioned, look out for smells or change your cleaning behaviour.
Make friends with your washing machine and clothes dryer, and make sure that freshly laundered clothing is immediately dried because even taking wet clothing, putting it through the dryer, has been shown to further reduce the presence of germs on the clothing. Remember high temperature for longer, at least 60 degrees Celsius, always use a detergent and make friends with your washing machine, improve your health and reduce skin infections. I hope this has been helpful. Stay well. See you next week.