Why do disinfectants only kill 99.9% of germs? Here’s the science
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Have you ever wondered why most disinfectants indicate they kill 99.9% or 99.99% of germs, but never promise to wipe out all of them? Perhaps the thought has crossed your mind mid-way through cleaning your kitchen or bathroom.
Surely, in a world where science is able to do all sorts of amazing things, someone would have invented a disinfectant that is 100% effective?
The answer to this conundrum requires understanding a bit of microbiology and a bit of mathematics.
What is a disinfectant?
A disinfectant is a substance used to kill or inactivate bacteria, viruses and other microbes on inanimate objects.
There are literally millions of microbes on surfaces and objects in our domestic environment. While most microbes are not harmful (and some are even good for us) a small proportion can make us sick.
Although disinfection can include physical interventions such as heat treatment or the use of UV light, typically when we think of disinfectants we are referring to the use of chemicals to kill microbes on surfaces or objects.
Chemical disinfectants often contain active ingredients such as alcohols, chlorine compounds and hydrogen peroxide which can target vital components of different microbes to kill them.
The maths of microbial elimination
In the past few years we’ve all become familiar with the concept of exponential growth in the context of the spread of COVID cases.
This is where numbers grow at an ever-accelerating rate, which can lead to an explosion in the size of something very quickly. For example, if a colony of 100 bacteria doubles every hour, in 24 hours’ time the population of bacteria would be more than 1.5 billion.
Conversely, the killing or inactivating of microbes follows a logarithmic decay pattern, which is essentially the opposite of exponential growth. Here, while the number of microbes decreases over time, the rate of death becomes slower as the number of microbes becomes smaller.
For example, if a particular disinfectant kills 90% of bacteria every minute, after one minute, only 10% of the original bacteria will remain. After the next minute, 10% of that remaining 10% (or 1% of the original amount) will remain, and so on.
Because of this logarithmic decay pattern, it’s not possible to ever claim you can kill 100% of any microbial population. You can only ever scientifically say that you are able to reduce the microbial load by a proportion of the initial population. This is why most disinfectants sold for domestic use indicate they kill 99.9% of germs.
Other products such as hand sanitisers and disinfectant wipes, which also often purport to kill 99.9% of germs, follow the same principle.
Real-world implications
As with a lot of science, things get a bit more complicated in the real world than they are in the laboratory. There are a number of other factors to consider when assessing how well a disinfectant is likely to remove microbes from a surface.
One of these factors is the size of the initial microbial population that you’re trying to get rid of. That is, the more contaminated a surface is, the harder the disinfectant needs to work to eliminate the microbes.
If for example you were to start off with only 100 microbes on a surface or object, and you removed 99.9% of these using a disinfectant, you could have a lot of confidence that you have effectively removed all the microbes from that surface or object (called sterilisation).
In contrast, if you have a large initial microbial population of hundreds of millions or billions of microbes contaminating a surface, even reducing the microbial load by 99.9% may still mean there are potentially millions of microbes remaining on the surface.
Time is is a key factor that determines how effectively microbes are killed. So exposing a highly contaminated surface to disinfectant for a longer period is one way to ensure you kill more of the microbial population.
This is why if you look closely at the labels of many common household disinfectants, they will often suggest that to disinfect you should apply the product then wait a specified time before wiping clean. So always consult the label on the product you’re using.
Other factors such as temperature, humidity and the type of surface also influence how well a disinfectant works outside the lab.
Similarly, microbes in the real world may be either more or less sensitive to disinfection than those used for testing in the lab.
Disinfectants are one part infection control
The sensible use of disinfectants plays an important role in our daily lives in reducing our exposure to pathogens (microbes that cause illness). They can therefore reduce our chances of getting sick.
The fact disinfectants can’t be shown to be 100% effective from a scientific perspective in no way detracts from their importance in infection control. But their use should always be complemented by other infection control practices, such as hand washing, to reduce the risk of infection.
Hassan Vally, Associate Professor, Epidemiology, Deakin University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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How To Ease Neck Pain At Home
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Dr. Bang is offering exercises to alleviate neck pain, which pain can be a real… Well, if only there were a good phrase for expressing how troublesome pain in that part of the body can be.
To be clear, he’s a doctor of chiropractic, not a medical doctor, but his advice has clearly been helping people alleviate pain, so without further ado, he advises the following things:
- Taking the head and neck slowly and carefully through the full range of motion available
- Contracting the neck muscles while repeating the above exercise, three times each way
- Backing off a little if it hurts at any point, but noting where the limits lie
- Repeating again the range of motion exercise, this time adding gentle resistance
- Holding each end of this for twenty seconds before releasing and doing the other side, three times each way
- Finally, stabilizing the head centrally and pushing into one’s hands, as an isometric strengthening exercise
He demonstrates each part clearly in this short (5:58) video:
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Want to know more about chiropractic?
You might like our previous main feature:
Is Chiropractic All It’s Cracked Up To Be?
Take care!
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Finding Peace at the End of Life – by Henry Fersko-Weiss
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This is not the most cheery book we’ve reviewed, but it is an important one. From its first chapter, with “a tale of two deaths”, one that went as well as can be reasonably expected, and the other one not so much, it presents a lot of choices.
The book is not prescriptive in its advice regarding how to deal with these choices, but rather, investigative. It’s thought-provoking, and asks questions—tacitly and overtly.
While the subtitle says “for families and caregivers”, it’s as much worth when it comes to managing one’s own mortality, too, by the way.
As for the scope of the book, it covers everything from terminal diagnosis, through the last part of life, to the death itself, to all that goes on shortly afterwards.
Stylewise, it’s… We’d call it “easy-reading” for style, but obviously the content is very heavy, so you might want to read it a bit at a time anyway, depending on how sensitive to such topics you are.
Bottom line: this book is not exactly a fun read, but it’s a very worthwhile one, and a good way to avoid regrets later.
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Eye Drops: Safety & Alternatives
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It’s Q&A Day at 10almonds!
Have a question or a request? You can always hit “reply” to any of our emails, or use the feedback widget at the bottom!
In cases where we’ve already covered something, we might link to what we wrote before, but will always be happy to revisit any of our topics again in the future too—there’s always more to say!
As ever: if the question/request can be answered briefly, we’ll do it here in our Q&A Thursday edition. If not, we’ll make a main feature of it shortly afterwards!
So, no question/request too big or small
❝Before important business meetings my father used to use eye drops to add a “sparkle” to his eyes. I think that is a step too far, but what, short of eye drops, can we do to keep our eyes bright throughout the day?❞
Firstly, we’d indeed not recommend eye drops unless advised to do so by your doctor to treat a specific health condition:
- Infections from over-the-counter artificial tears
- Are my eye drops safe to use?
- More eye drops recalled due to infection danger
Those eye drops that “add sparkle” are often based on astringents such as witch hazel. This means that the capillaries in the eye undergo vasoconstriction, becoming much less visible and the eye thus appears much whiter and thus brighter.
There isn’t a way to do the same thing from the inside, as taking a vasoconstrictor will simply increase your general blood pressure, making the capillaries of your eyes more, rather than less, visible.
However, what you can do is…
- look after your general vasculature (cardiovascular health)
- in particular, reduce hypertension
- that includes limiting salt
- stay away from vasoconstrictors (including caffeine)
- reduce your resting cortisol levels
- that certainly also means reducing alcohol consumption
- maintain good hydration
Take care!
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The Pain Relief Secret – by Sarah Warren
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This one’s a book to not judge by the cover—or the title. The title is actually accurate, but it sounds like a lot of woo, doesn’t it?
Instead, what we find is a very clinical, research-led (40 pages of references!) explanation of:
- the causes of musculoskeletal pain
- how this will tend to drive us to make it worse
- what we can do instead to make it better
A lot of this, to give you an idea what to expect, hinges on the fact that bones only go where muscles allow/move them; muscles only behave as instructed by nerves, and with a good development of biofeedback and new habits to leverage neuroplasticity, we can take more charge of that than you might think.
Warning: you may want to jump straight into the part with the solutions, but if you do so without a very good grounding in anatomy and physiology, you may find yourself out of your depth with previously-explained terms and concepts that are now needed to understand (and apply) the solutions.
However, if you read it methodically cover-to-cover, you’ll find you need no prior knowledge to take full advantage of this book; the author is a very skilled educator.
Bottom line: while it’s not an overnight magic pill, the methodology described in this book is a very sound way to address the causes of musculoskeletal pain.
Click here to check out The Pain Relief Secret, and help your body undo damage done!
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It’s Not Fantastic To Be Plastic
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We Are Such Stuff As Bottles Are Made Of
We’ve written before about PFAS, often found in non-stick coatings and the like:
PFAS Exposure & Cancer: The Numbers Are High
Today we’re going to be talking about microplastics & nanoplastics!
What are microplastics and nanoplastics?
Firstly, they’renot just the now-banned plastic microbeads that have seen some use is toiletries (although those are classified as microplastics too).
Many are much smaller than that, and if they get smaller than a thousandth of a millimeter, then they get the additional classification of “nanoplastic”.
In other words: not something that can be filtered even if you were to use a single-micron filter. The microplastics would still get through, for example:
Scientists find about a quarter million invisible nanoplastic particles in a liter of bottled water
And unfortunately, that’s bad:
❝What’s disturbing is that small particles can appear in different organs and may cross membranes that they aren’t meant to cross, such as the blood-brain barrier❞
Note: they’re crossing the same blood-brain barrier that many of our nutrients and neurochemicals are too big to cross.
These microplastics are also being found in arterial plaque
What makes arterial plaque bad for the health is precisely its plasticity (the arterial walls themselves are elastic), so you most certainly do not want actual plastic being used as part of the cement that shouldn’t even be lining your arteries in the first place:
Microplastics found in artery plaque linked with higher risk of heart attack, stroke and death
❝In this study, patients with carotid artery plaque in which MNPs were detected had a higher risk of a composite of myocardial infarction, stroke, or death from any cause at 34 months of follow-up than those in whom MNPs were not detected❞
~ Dr. Raffaele Marfella et al.
(MNP = Micro/Nanoplastics)
Source: Microplastics and Nanoplastics in Atheromas and Cardiovascular Events
We don’t know how bad this is yet
There are various ways this might not be as bad as it looks (the results may not be repeated, the samples could have been compromised, etc), but also, perhaps cynically but nevertheless honestly, it could also be worse than we know yet—only more experiments being done will tell us which.
In the meantime, here’s a rundown of what we do and don’t know:
Study links microplastics with human health problems—but there’s still a lot we don’t know
Take care!
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Calm Your Mind with Food – by Dr. Uma Naidoo
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From the author of This Is Your Brain On Food, the psychiatrist-chef (literally, she is a Harvard-trained psychiatrist and an award-winning chef) is back with a more specific work, this time aimed squarely at what it says in the title; how to calm your mind with food.
You may be wondering: does this mean comfort-eating? And, well, not in the sense that term’s usually used. There will be eating and comfort will occur, but the process involves an abundance of nutrients, a minimization of health-deleterious ingredients, and a “for every chemical its task” approach. In other words, very much “nutraceuticals”, as our diet.
On which note: as we’ve come to expect from Dr. Naidoo, we see a lot of hard science presented simply and clearly, with neither undue sensationalization nor unnecessary jargon. We learn about the brain, the gut, relevant biology and chemistry, and build up from understanding ingredients to dietary patterns to having a whole meal plan, complete with recipes.
You may further be wondering: how much does it add that we couldn’t get from the previous book? And the answer is, not necessarily a huge amount, especially if you’re fairly comfortable taking ideas and creating your own path forwards using them. If, on the other hand, you’re a little anxious about doing that (as someone perusing this book may well be), then Dr. Naidoo will cheerfully lead you by the hand through what you need to know and do.
Bottom line: if not being compared to her previous book, this is a great standalone book with a lot of very valuable content. However, the previous book is a tough act to follow! So… All in all we’d recommend this more to people who want to indeed “calm your mind with food”, who haven’t read the other book, as this one will be more specialized for you.
Click here to check out Calm Your Mind With Food, and do just that!
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