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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Why do some people’s hair and nails grow quicker than mine?
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Throughout recorded history, our hair and nails played an important role in signifying who we are and our social status. You could say, they separate the caveman from businessman.
It was no surprise then that many of us found a new level of appreciation for our hairdressers and nail artists during the COVID lockdowns. Even Taylor Swift reported she cut her own hair during lockdown.
So, what would happen if all this hair and nail grooming got too much for us and we decided to give it all up. Would our hair and nails just keep on growing?
The answer is yes. The hair on our head grows, on average, 1 centimeter per month, while our fingernails grow an average of just over 3 millimetres.
When left unchecked, our hair and nails can grow to impressive lengths. Aliia Nasyrova, known as the Ukrainian Rapunzel, holds the world record for the longest locks on a living woman, which measure an impressive 257.33 cm.
When it comes to record-breaking fingernails, Diana Armstrong from the United States holds that record at 1,306.58 cm.
Most of us, however, get regular haircuts and trim our nails – some with greater frequency than others. So why do some people’s hair and nails grow more quickly?
Jari Lobo/Pexels Remind me, what are they made out of?
Hair and nails are made mostly from keratin. Both grow from matrix cells below the skin and grow through different patterns of cell division.
Nails grow steadily from the matrix cells, which sit under the skin at the base of the nail. These cells divide, pushing the older cells forward. As they grow, the new cells slide along the nail bed – the flat area under the fingernail which looks pink because of its rich blood supply.
Nails, like hair, are made mostly of keratin. Scott Gruber/Unsplash A hair also starts growing from the matrix cells, eventually forming the visible part of the hair – the shaft. The hair shaft grows from a root that sits under the skin and is wrapped in a sac known as the hair follicle.
This sac has a nerve supply (which is why it hurts to pull out a hair), oil-producing glands that lubricate the hair and a tiny muscle that makes your hair stand up when it’s cold.
At the follicle’s base is the hair bulb, which contains the all-important hair papilla that supplies blood to the follicle.
Matrix cells near the papilla divide to produce new hair cells, which then harden and form the hair shaft. As the new hair cells are made, the hair is pushed up above the skin and the hair grows.
But the papilla also plays an integral part in regulating hair growth cycles, as it sends signals to the stem cells to move to the base of the follicle and form a hair matrix. Matrix cells then get signals to divide and start a new growth phase.
Unlike nails, our hair grows in cycles
Scientists have identified four phases of hair growth, the:
- anagen or growth phase, which lasts between two and eight years
- catagen or transition phase, when growth slows down, lasting around two weeks
- telogen or resting phase, when there is no growth at all. This usually lasts two to three months
- exogen or shedding phase, when the hair falls out and is replaced by the new hair growing from the same follicle. This starts the process all over again.
Hair follicles enter these phases at different times so we’re not left bald. Mosterpiece/Shutterstock Each follicle goes through this cycle 10–30 times in its lifespan.
If all of our hair follicles grew at the same rate and entered the same phases simultaneously, there would be times when we would all be bald. That doesn’t usually happen: at any given time, only one in ten hairs is in the resting phase.
While we lose about 100–150 hairs daily, the average person has 100,000 hairs on their head, so we barely notice this natural shedding.
So what affects the speed of growth?
Genetics is the most significant factor. While hair growth rates vary between individuals, they tend to be consistent among family members.
Nails are also influenced by genetics, as siblings, especially identical twins, tend to have similar nail growth rates.
Genetics have the biggest impact on growth speed. Cottonbro Studio/Pexels But there are also other influences.
Age makes a difference to hair and nail growth, even in healthy people. Younger people generally have faster growth rates because of the slowing metabolism and cell division that comes with ageing.
Hormonal changes can have an impact. Pregnancy often accelerates hair and nail growth rates, while menopause and high levels of the stress hormone cortisol can slow growth rates.
Nutrition also changes hair and nail strength and growth rate. While hair and nails are made mostly of keratin, they also contain water, fats and various minerals. As hair and nails keep growing, these minerals need to be replaced.
That’s why a balanced diet that includes sufficient nutrients to support your hair and nails is essential for maintaining their health.
Nutrition can impact hair and nail growth. Cottonbro Studio/Pexels Nutrient deficiencies may contribute to hair loss and nail breakage by disrupting their growth cycle or weakening their structure. Iron and zinc deficiencies, for example, have both been linked to hair loss and brittle nails.
This may explain why thick hair and strong, well-groomed nails have long been associated with perception of good health and high status.
However, not all perceptions are true.
No, hair and nails don’t grow after death
A persistent myth that may relate to the legends of vampires is that hair and nails continue to grow after we die.
In reality, they only appear to do so. As the body dehydrates after death, the skin shrinks, making hair and nails seem longer.
Morticians are well aware of this phenomenon and some inject tissue filler into the deceased’s fingertips to minimise this effect.
So, it seems that living or dead, there is no escape from the never-ending task of caring for our hair and nails.
Michelle Moscova, Adjunct Associate Professor, Anatomy, UNSW Sydney
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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Hope: A research-based explainer
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This year, more than 60 countries, representing more than 4 billion people, will hold major elections. News headlines already are reporting that voters are hanging on to hope. When things get tough or don’t go our way, we’re told to hang on to hope. HOPE was the only word printed on President Barack Obama’s iconic campaign poster in 2008.
Research on hope has flourished only in recent decades. There’s now a growing recognition that hope has a role in physical, social, and mental health outcomes, including promoting resilience. As we embark on a challenging year of news, it’s important for journalists to learn about hope.
So what is hope? And what does the research say about it?
Merriam-Webster defines hope as a “desire accompanied by expectation of or belief in fulfillment.” This definition highlights the two basic dimensions of hope: a desire and a belief in the possibility of attaining that desire.
Hope is not Pollyannaish optimism, writes psychologist Everett Worthington in a 2020 article for The Conversation. “Instead, hope is a motivation to persevere toward a goal or end state, even if we’re skeptical that a positive outcome is likely.”
There are several scientific theories about hope.
One of the first, and most well-known, theories on hope was introduced in 1991 by American psychologist Charles R. Snyder.
In a paper published in the Journal of Personality and Social Psychology, Snyder defined hope as a cognitive trait centered on the pursuit of goals and built on two components: a sense of agency in achieving a goal, and a perceived ability to create pathways to achieve that goal. He defined hope as something individualistic.
Snyder also introduced the Hope Scale, which continues to be used today, as a way to measure hope. He suggested that some people have higher levels of hope than others and there seem to be benefits to being more hopeful.
“For example, we would expect that higher as compared with lower hope people are more likely to have a healthy lifestyle, to avoid life crises, and to cope better with stressors when they are encountered,” they write.
Others have suggested broader definitions.
In 1992, Kaye Herth, a professor of nursing and a scholar on hope, defined hope as “a multidimensional dynamic life force characterized by a confident yet uncertain expectation of achieving good, which to the hoping person, is realistically possible and personally significant.” Herth also developed the Herth Hope Index, which is used in various settings, including clinical practice and research.
More recently, others have offered an even broader definition of hope.
Anthony Scioli, a clinical psychologist and author of several books on hope, defines hope “as an emotion with spiritual dimensions,” in a 2023 review published in Current Opinion in Psychology. “Hope is best viewed as an ameliorating emotion, designed to fill the liminal space between need and reality.”
Hope is also nuanced.
“Our hopes may be active or passive, patient or critical, private or collective, grounded in the evidence or resolute in spite of it, socially conservative or socially transformative,” writes Darren Webb in a 2007 study published in History of the Human Sciences. “We all hope, but we experience this most human of all mental feelings in a variety of modes.”
To be sure, a few studies have shown that hope can have negative outcomes in certain populations and situations. For example, one study highlighted in the research roundup below finds that Black college students who had higher levels of hope experienced more stress due to racial discrimination compared with Black students who had lower levels of hope.
Today, hope is one of the most well-studied constructs within the field of positive psychology, according to the journal Current Opinion in Psychology, which dedicated its August 2023 issue to the subject. (Positive psychology is a branch of psychology focused on characters and behaviors that allow people to flourish.)
We’ve gathered several studies below to help you think more deeply about hope and recognize its role in your everyday lives.
Research roundup
The Role of Hope in Subsequent Health and Well-Being For Older Adults: An Outcome-Wide Longitudinal Approach
Katelyn N.G. Long, et al. Global Epidemiology, November 2020.The study: To explore the potential public health implications of hope, researchers examine the relationship between hope and physical, behavioral and psychosocial outcomes in 12,998 older adults in the U.S. with a mean age of 66.
Researchers note that most investigations on hope have focused on psychological and social well-being outcomes and less attention has been paid to its impact on physical and behavioral health, particularly among older adults.
The findings: Results show a positive association between an increased sense of hope and a variety of behavioral and psychosocial outcomes, such as fewer sleep problems, more physical activity, optimism and satisfaction with life. However, there wasn’t a clear association between hope and all physical health outcomes. For instance, hope was associated with a reduced number of chronic conditions, but not with stroke, diabetes and hypertension.
The takeaway: “The later stages of life are often defined by loss: the loss of health, loved ones, social support networks, independence, and (eventually) loss of life itself,” the authors write. “Our results suggest that standard public health promotion activities, which often focus solely on physical health, might be expanded to include a wider range of factors that may lead to gains in hope. For example, alongside community-based health and nutrition programs aimed at reducing chronic conditions like hypertension, programs that help strengthen marital relations (e.g., closeness with a spouse), provide opportunities to volunteer, help lower anxiety, or increase connection with friends may potentially increase levels of hope, which in turn, may improve levels of health and well-being in a variety of domains.”
Associated Factors of Hope in Cancer Patients During Treatment: A Systematic Literature Review
Corine Nierop-van Baalen, Maria Grypdonck, Ann van Hecke and Sofie Verhaeghe. Journal of Advanced Nursing, March 2020.The study: The authors review 33 studies, written in English or Dutch and published in the past decade, on the relationship between hope and the quality of life and well-being of patients with cancer. Studies have shown that many cancer patients respond to their diagnosis by nurturing hope, while many health professionals feel uneasy when patients’ hopes go far beyond their prognosis, the authors write.
The findings: Quality of life, social support and spiritual well-being were positively associated with hope, as measured with various scales. Whereas symptoms, psychological distress and depression had a negative association with hope. Hope didn’t seem to be affected by the type or stage of cancer or the patient’s demographics.
The takeaway: “Hope seems to be a process that is determined by a person’s inner being rather than influenced from the outside,” the authors write. “These factors are typically given meaning by the patients themselves. Social support, for example, is not about how many patients experience support, but that this support has real meaning for them.”
Characterizing Hope: An Interdisciplinary Overview of the Characteristics of Hope
Emma Pleeging, Job van Exel and Martijn Burger. Applied Research in Quality of Life, September 2021.The study: This systematic review provides an overview of the concept of hope based on 66 academic papers in ten academic fields, including economics and business studies, environmental studies, health studies, history, humanities, philosophy, political science, psychology, social science, theology and youth studies, resulting in seven themes and 41 sub-themes.
The findings: The authors boil down their findings to seven components: internal and external sources, the individual and social experience of hope, internal and external effects, and the object of hope, which can be “just about anything we can imagine,” the authors write.
The takeaway: “An important implication of these results lies in the way hope is measured in applied and scientific research,” researchers write. “When measuring hope or developing instruments to measure it, researchers could be well-advised to take note of the broader understanding of the topic, to prevent that important characteristics might be overlooked.”
Revisiting the Paradox of Hope: The Role of Discrimination Among First-Year Black College Students
Ryon C. McDermott, et al. Journal of Counseling Psychology, March 2020.The study: Researchers examine the moderating effects of hope on the association between experiencing racial discrimination, stress and academic well-being among 203 first-year U.S. Black college students. They build on a small body of evidence that suggests high levels of hope might have a negative effect on Black college students who experience racial discrimination.
The authors use data gathered as part of an annual paper-and-pencil survey of first-year college students at a university on the Gulf Coast, which the study doesn’t identify.
The findings: Researchers find that Black students who had higher levels of hope experienced more stress due to racial discrimination compared with students who had lower levels of hope. On the other hand, Black students with low levels of hope may be less likely to experience stress when they encounter discrimination.
Meanwhile, Black students who had high levels of hope were more successful in academic integration — which researchers define as satisfaction with and integration into the academic aspects of college life — despite facing discrimination. But low levels of hope had a negative impact on students’ academic well-being.
“The present study found evidence that a core construct in positive psychology, hope, may not always protect Black students from experiencing the psychological sting of discrimination, but it was still beneficial to their academic well-being,” the authors write.
The takeaway: “Our findings also highlight an urgent need to reduce discrimination on college campuses,” the researchers write. “Reducing discrimination could help Black students (and other racial minorities) avoid additional stress, as well as help them realize the full psychological and academic benefits of having high levels of hope.”
Additional reading
Hope Across Cultural Groups Lisa M. Edwards and Kat McConnell. Current Opinion in Psychology, February 2023.
The Psychology of Hope: A Diagnostic and Prescriptive Account Anthony Scioli. “Historical and Multidisciplinary Perspectives on Hope,” July 2020.
Hope Theory: Rainbows in the Mind C.R. Snyder. Psychological Inquiry, 2002
This article first appeared on The Journalist’s Resource and is republished here under a Creative Commons license.
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Goat Milk Greek Yogurt vs Almond Milk Greek Yogurt – Which is Healthier?
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Our Verdict
When comparing goat milk yogurt to almond milk yogurt, we picked the almond milk yogurt.
Why?
Surprised? Honestly, we were too!
Much as we love almonds, we were fully expecting to write about how they’re very close in nutritional value, but the dairy yogurt has more probiotics, but no, as it turns out when we looked into them, they’re quite comparable in that regard.
It’s easy to assume “goat milk yogurt is more natural and therefore healthier”, but in both cases, it was a case of taking a fermentable milk, and fermenting it (an ancient process). “But almond milk is a newfangled thing”, well, new-ish…
So what was the deciding factor?
In this case, the almond milk yogurt has about twice the protein per (same size) serving, compared to the goat milk; all the other macros are about the same, and the micronutrients are similar. Like many plant-based milks and yogurts, this one is fortified with calcium and vitamin D, so that wasn’t an issue either.
In short: the only meaningful difference was the protein, and the almond came out on top.
However!
The almond came out on top only because it is strained; this can be done (or not) with any kind of yogurt, be it from an animal or a plant.
In other words: if it had been different brands, the goat milk yogurt could have come out on top!
The take-away idea here is: always read labels, because as you’ve just seen, even we can get surprised sometimes!
seriously if you only remember one thing from this today, make it the above
Other thing worth mentioning: yogurts, and dairy products in general, are often made with common allergens (e.g. dairy, nuts, soy, etc). So if you are allergic or intolerant, obviously don’t choose the one to which you are allergic or intolerant.
That said… If you are lactose-intolerant, but not allergic, goat’s milk does have less lactose than cow’s milk. But of course, you know your limits better than we can in this regard.
Want to try some?
Amazon is not coming up with the goods for this one (or anything even similar, at time of writing), so we recommend trying your local supermarket (and reading labels, because products vary widely!)
What you’re looking for (be it animal- or plant-based):
- Live culture probiotic bacteria
- No added sugar
- Minimal additives in general
- Lastly, check out the amounts for protein, calcium, vitamin D, etc.
Enjoy!
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Running: Getting Started – by Jeff Galloway
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Superficially, running is surely one of the easiest sports to get into, for most people. You put one foot in front of the other, repeat, and pick up the pace.
However, many people do not succeed. They head out of the door (perhaps on January the first), push themselves a little, experience runner’s high, think “this is great”, and the next day wake up with some minor aches and no motivation. This book is here to help you bypass that stage.
Jeff Galloway has quite a series of books, but the others seem derivative of this one. So, what makes this one special?
It’s quite comprehensive; it covers (as the title promises) getting started, setting yourself up for success, finding what level your ability is at safely rather than guessing and overdoing it, and building up from there.
He also talks about what kit you’ll want; this isn’t just about shoes, but even “what to wear when the weather’s not good” and so forth; he additionally shares advice about diet, exercise on non-running days, body maintenance (stretching and strengthening), troubleshooting aches and pains, and running well into one’s later years.
Bottom line: if you’d like to take up running but it seems intimidating (perhaps for reasons you can’t quite pin down), this book will take care of all those things, and indeed get you “up and running”.
Click here to check out Running: Getting Started, and get started!
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The Natural Facelift – by Sophie Perry
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First, what this book isn’t: it’s mostly not about beauty, and it’s certainly not about ageist ideals of “hiding” aging.
The author herself discusses the privilege that is aging (not everyone gets to do it) and the importance of taking thankful pride in our lived-in bodies.
The title and blurb belie the contents of the book rather. Doubtlessly the publisher felt that extrinsic beauty would sell better than intrinsic wellbeing. As for what it’s actually more about…
Ever splashed your face in cold water to feel better? This book’s about revitalising the complex array of facial muscles (there are anatomical diagrams) and the often-tired and very diverse tissues that cover them, complete with the array of nerve endings very close to your CNS (not to mention the vagus nerve running just behind your jaw), and some of the most important blood vessels of your body, serving your brain.
With all that in mind, this book, full of useful therapeutic techniques, is a very, very far cry from “massage like this and you’ll look like you got photoshopped”.
The style varies, as some parts of explanation of principles, or anatomy, and others are hands-on (literally) guides to the exercises, but it is all very clear and easy to understand/follow.
Bottom line: aspects of conventional beauty may be a side-effect of applying the invigorating exercises described in this book. The real beauty is—literally—more than skin-deep.
Click here to check out The Natural Facelift, and order yours!
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The Cancer Journey – by Dr. Chadi Nabhan
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After a brief introduction of what cancer actually is and what causes it, the layout of the rest of the book is in chronological order of patient experience, that is to say, what to expect during the journey from screening and diagnosis, to one’s first oncology visit (the author being an oncologist himself), how cancer staging works, getting second opinions, and a chapter-by-chapter review of many different treatment options, ranging from surgery and chemotherapy, to radiation and hormonal therapies, and even more modern targeted therapies, immunotherapy, cellular therapies, and yes, complementary and alternative therapies, amongst others we haven’t listed for the sake of brevity.
He doesn’t leave it there though; he also talks managing side effects, monitoring for recurrence, and even caring for the caregiver(s), along with eventual survivorship and that emotional journey, or if it comes down to it, palliative and hospice care.
Finishing on a hopeful note, he also brings attention to novel approaches that are being trialled presently, and the prospects for the near future of cancer care.
The style is very human and readable, notwithstanding that the author has hundreds of peer-reviewed publications to his name, the content here is presented in a much more approachable, less clinical way, while still conveying all the information that needs to be conveyed.
Bottom line: if you or a loved one is facing cancer, this book will be an invaluable resource.
Click here to check out The Cancer Journey, and understand each part of it!
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