Tag Archives: soap

Physics sheds light on the 20-second handwashing rule. Here’s why it’s so effective

Physics plays a big role into clean hands. (Image: Pixabay)

In the past several months, the CDC has touted 20 seconds as the standard for all hand-washing activities, bringing a number of rarely sung happy birthdays, fight songs, and other multiple-second ditties out of the closet as a counter for the time period.

However, studies were short on why exactly 20 is the magic number. Well, now there is one.

Harder, better, faster, washer

In a new report out of the American Institute of Physics published in Physics of Fluids, researchers have created a model which captures the key mechanics of hand-washing. Turns out faster hand movement is better.

By simulating the motion you make when cleaning your hands, researchers estimated the time scales on which particles like viruses and bacteria were removed from your hands. Their model acted in two dimensions, with a wavy surface moving past another with a thin film of liquid separating the two — it’s imperfect but still good enough to get an idea. These wavy surfaces represented hands in their model due to the surface harshness on small spatial scales.

Particles would be trapped on the rough surfaces in wells of the hands, like the bottom of a valley. Vigorous movement and high water pressure would bring the particles to the surface and out of their little valley homes and out of your skin. According to Paul Hammond, author of the report, it turns out that 20 seconds is what he came up with in his model as the time to dislodge these particles from your hands.

“Basically, the flow tells you about the forces on the particles. Then you can work out how the particles move and figure out if they get removed,” said Hammond, who likened the process to scrubbing a stain on a shirt where the faster the motion the more likely it is to remove it. “If you move your hands too gently, too slowly, relative to one another, the forces created by the flowing fluid are not big enough to overcome the force holding the particle down.”

Hammond states that the model does not take into account chemical or biological processes that occur when using soap, but it’s pretty well known across the board that soap only improves the probability that your hands will, in fact, become cleaner.

“These viruses have membranes that surround the genetic particles that are called lipid membranes because they have an oily, greasy structure,” Thomas Gilbert, an associate professor of chemistry and chemical biology at Northeastern University, told the BBC. “It’s this kind of structure than be neutralized by soap and water.”

He explained that the dissolving of the outer “envelope” breaks up virus cells, and the genetic material, which is the RNA that takes over human cells in order to make copies of the virus, is swept away and destroyed because of the chemical or biological agents.

Just knowing how the physics of handwashing works can give us some clues as to how we can create more effective and environmentally friendly soaps, the researcher concludes.

“Nowadays, we need to be a bit more thoughtful about what happens to the wash chemicals when they go down the plughole and enter the environment.”

In the end, there is much more that goes into the story of handwashing, but this study does explain some puzzles and lay the foundation for future research. Truth be told, we’ve learned in the pandemic that we could all use a bit of work on our handwashing.

How good hand-washing beats COVID-19 (and other contagious diseases)

Image via MSU Today.

The most important piece of advice we need to follow to help us stay safe from COVID-19 is this one: wash your hands.

SARS-CoV-2, the virus causing COVID-19, and other respiratory viruses spreads easily by droplets from breathing, coughing and sneezing. Because our hands touch many surfaces, they can pick up microbes, including viruses. Then by touching contaminated hands to your eyes, nose, or mouth, the pathogens can infect the body.

Coronaviruses, like this year’s novel coronavirus called SARS-CoV-2 that has infected over 110,000 worldwide are encased in a lipid envelope — basically, a layer of fat. Soap can break that fat apart and make the virus unable to infect you.

There are two ways to decrease the number of microbes on your hands.


First strategy: decrease the overall biomass of microbes – that is, decrease the amount of bacteria, viruses and other types of microorganisms. We do this by washing out hands with soap and rinsing with water. When you wash your hands with soap and water, the soap chemically works to break down the oil, while the friction from rubbing does it mechanically. The more soap and the longer the hands are rubbed together, once rinsed away with water, the less oil and microbes are left on your hands. Public health experts agree that this method of hand washing, for at least 20 or more seconds at a time,

From the European Centre for Disease Prevention and Control (ECDC)

Second strategy: kill the microbes. We do this by using products with an antibacterial agent such as alcohols, chlorine, peroxides, chlorhexidine or triclosan. However, the efficacy on these agents can vary depending on the concentration of the antibacterial agent and on the particular microbe.

What about bar soap? Numerous studies have found that bacteria can stay on bar soap that stays wet because it gets used frequently. But studies that have shown that bacteria don’t seem to transfer to the next user. If the bar of soap looks slimy, rinse it off under water before you lather your hands, and try to store it so it will dry out between uses.

What if there’s no soap? If you’re in a public bathroom, and there’s no soap, just rubbing your hands together under the water does do some good. A 2011 study from researchers at the London School of Tropical Hygiene found that washing with water alone reduced bacteria on hands to about one-quarter of their prewash state. Washing with soap and water brought bacterial counts down to about 8% of where they were before washing.

What if there’s no soap or water? You can use hand sanitizers. Lipid membrane viruses like coronaviruses are killed by alcohol-based hand sanitizer as long as it is at least 62% alcohol. Make sure to use enough so that it covers all the surfaces on your hands. Rub that on until your hands feel dry, which should take about 20 seconds. Alcohol kills some bacteria and viruses by breaking down their protective membranes, which basically makes them fall apart. But it doesn’t work for all germs, such as norovirus, Clostridium difficile, which can cause life-threatening diarrhea, or Cryptosporidium, a parasite that causes a diarrheal disease called cryptosporidiosis. But it works very well for enveloped viruses such as Hepatitis B virus, influenza virus, and coronaviruses!

What about drying hands with paper towels? Paper towels have a beneficial effect beyond simply washing. Rubbing your hands with a paper towel removes even more germs than washing alone. Dry hands are also less likely to spread contamination than wet hands.

How often do you need to wash? A lot. The CDC says to wash your hands:

  • Before, during, and after preparing food;
  • Before eating;
  • Before and after taking care of someone sick;
  • Before and after treating a cut or other wound;
  • After going to the bathroom;
  • After changing diapers or helping a child in the bathroom;
  • After blowing your nose, coughing, or sneezing;
  • After touching an animal, or touching pet food or pet waste;
  • After handling pet food or pet treats;
  • After touching garbage.

With all the messaging in the news, on social media, and elsewhere about COVID-19 you’re probably doing a lot more hand washing than you’re used to. But regular and proper handwashing should be done all the time and not just during outbreaks.

And remember after washing, try to keep your hands clean. Avoid touching contaminated surfaces. Use a clean paper towel to open bathroom doors. Disinfect dirty surfaces that you use every day, like the touchscreen on your phone and your computer keyboard.

New study points the way to rice straw soaps

Researchers at the University of Portsmouth have developed a novel way to make soaps — out of rice straw.

Image via Pixabay.

Rice straw is one of the most abundant, readily available, cheap, and underused resources. Now, an innovative research effort from the University of Portsmouth has shown that bails of rice straw could create a ‘biosurfacant’ (surfactants are basically soaps). The findings point the way towards non-toxic alternatives for petroleum-based materials used in a wide range of products.

Straw-scented soap

“Surfactants are everywhere, including detergent, fabric softener, glue, insecticides, shampoo, toothpaste, paint, laxatives and makeup,” explains Dr. Pattanathu Rahman, microbial biotechnologist from the University of Portsmouth and study co-author. “Imagine if we could make and manufacture biosurfacants in sufficient quantities to use instead of surfactants, taking the manmade chemical bonds out of these products.”

“This research shows that with the use of agricultural waste such as rice straws, which is in plentiful supply, we are a step closer.”

The team embarked on the project in an effort to find ways of reducing the need for artificial chemical compounds used in industry and daily life applications. They were aided in their research by members from the University of Portsmouth’s Centre for Enzyme Innovation, the Amity University in India, and the Indian Institute of Technology.

Their research focused on alternatives for chemical surfactants from day one, as this is a key chemical class in use today. Surfactants are the main active ingredient in the production of cleaning products, medicine, sunscreen, makeup, and insecticides. They’re so important because they can tie oil and water molecules together and lower the surface tension of liquids — i.e., they make it possible for us to wash oil and fats with water.

Rice straw.
Image via Pixabay.

Dr. Rahman’s (who is also the Director of TeeGene Biotech Ltd in the UK) team sought to create a biosurfacant by brewing rice straw with enzymes. Rice straw was selected as it’s readily available waste produced in huge quantities every year. The team was also confident that the straw-based method could produce the kind of high-quality materials that manufacturing industries keep an eye out for. The method also has a number of positive ecological effects:

  • Rice straw is a natural byproduct of the rice harvest, with millions of tons created worldwide every year; the method would help put that waste material to productive use.
  • Tied to the previous point, farmers make a habit of burning rice straws to get rid of it. Finding an economic use for this material could help reduce emissions and potentially give farmers an extra source of income.
  • A biosurfactant would help appease concerns about the impact of chemical surfactants used in household products, most of which end up in the oceans.

“The levels of purity needed for biosurfactants in the industries in which they’re used is extremely high,” Dr. Rahman explains. “Because of this, they can be very expensive.”

“However, the methods we have of producing them make it much more economical and cost efficient. It’s a very exciting technology with tremendous potential for applications in a range of industries.”

The study reports that biosurfactants could be a viable alternative to synthetic ones, with a possible market value of $US2.8 billion by 2023. Among their comparative advantages, the study lists their low toxicity, biodegradable nature, and specificity — the last point would help them meet the European Surfactant Directive.

“Most people consider soap to be an effective means of removing bacteria from their skin. However, we have flipped this concept on its head by discovering a way to create soap from bacteria,” Dr. Rahman concludes.

“They have antimicrobial properties suitable for cosmetic products and biotherapeutics. This approach will channelise the majority of the waste management solutions and could create new job opportunities.”

The paper “Statistical and sequential (fill-and-draw) approach to enhance rhamnolipid production using industrial lignocellulosic hydrolysate C6 stream from Achromobacter sp. (PS1)” has been published in the journal Bioresource Technology.

This Canadian startup is turning CO2 emissions into soap

Solving our current climate emergency requires immediate action in order to reduce the amount of carbon already dumped into the atmosphere by human activities. This is a huge challenge for a number of reasons and it won’t certainly happen overnight — which is why mitigating strategies such as capturing and sequestering carbon have gained so much attention.

But what if you could capture carbon and find a way to turn a profit as well? For instance, by turning some of that carbon into a useful product that people value and would be willing to buy it. That would be fantastic since it would provide a genuine economic incentive (in contrast to a discouraging incentive like as a carbon tax) to take action.

This is what a Canadian startup CleanO2 was founded for. The company sells a device, called CARBiNX, which captures CO2 emissions from industrial furnaces and boilers and turns it into potash — a potassium-rich salt.

The potash is then used to make soaps, detergents, and other products in the pharmaceutical industry and agriculture sector. The famous Lush Cosmetics chain is one of the clients that use potash from CleanO2 in some of its products.

CARBiNX, which is about the size of two refrigerators, captures carbon emissions by using a hydroxide chemical to absorb it. The chemical reaction produces potash, which can be sold. The profit is then shared between the startup and the owner of the unit. According to CleanO2, their products pay for themselves within four to five years.

The heat from the chemical reaction can also be exploited to drive down a facility’s energy cost. For instance, it could be used to pre-warm water for a boiler.

The CARBiNX unit. Credit: CleanO2.

At the moment, there are 14 CARBiNX units installed in Alberta and British Columbia. These unit are expected to sequester 5 to 6 tonnes of CO2 annually. The company wants to install 40 units by the end of the year and more than 1,000 by 2020.

Elsewhere, other companies and research groups are also working on technologies that capture CO2 and convert it into commercial products, such as construction materials and synthetic fuels. And, in an ironic turn of events, one group comprised of scientists from Australia, Germany, China, and the US has developed a method that turns CO2 back into coal to be buried in the ground.

This won’t solve our carbon problem — not even close. It’s a minuscule step in a marathon race, but at the end of the day, may minuscule steps can add up and make a big difference.

Antimicrobials do more harm than good, according to statement signed by 200 researchers

Researchers warn against using antimicrobial soaps. Image credits: Darren Hester / Flickr.

If you’re using antimicrobial soaps, you might want to reconsider that. Sure, you think you’re doing the best, but according to a statement published in a peer-reviewed journal called Environmental Health Perspectives by over 200 scientists and health professionals, you’re not doing anyone any favors. In fact, you might be doing more harm than good.

The paper, signed by people from 29 different countries, discusses not only the lack of evidence related to the benefits of antimicrobial soaps but also the health and ecological hazards associated with them. They also released this cute video which showcases the gist of their publication.

“People think antimicrobial hand soaps offer better protection against illness. But generally, antimicrobial soaps perform no better than plain soap and water,” said Barbara Sattler, RN, DrPH, FAAN, environmental health professor at the University of San Francisco.

The two most famous and widely used antimicrobial substances are the infamous triclosan and triclocarban. For starters, both substances are endocrine disruptors, which means they interfere with important hormonal processes. This can directly or indirectly affect our immune system as well as our brain — thyroid, testosterone, and estrogen regulation are especially affected. A large study has also linked triclosan, which is also used in other products like detergents, to cancer. They also end up, in a variety of forms, in natural environments, causing significant damage. To make things even worse, we are facing a global drug-resistance crisis, largely powered by our overuse of antimicrobial products. But perhaps the most important reason why you shouldn’t use antimicrobial soaps is that they don’t work.

Study after study has shown that washing your hands with water and regular soap (be it cold or warm water) is just as effective as using antimicrobial soaps. There are very few — if any — proved benefits, and yet people still opt for such products. Thankfully, the U.S. Food and Drug Administration (FDA) ruled that 19 different antimicrobial chemicals, including triclosan and triclocarban, were not effective, and there is no evidence they are safe either. So they effectively banned these substances from soaps, but like a hydra with many heads, other antimicrobial substances popped up to replace them — and these substitutes may be even worse. To make things even worse, it’s not just soaps. Nowadays, antimicrobials appear in a number of products you’d never expect them, such as paints, exercise mats, flooring, apparel, food storage containers, home textiles, electronics, kitchenware, school supplies, and countertops.

 “I was happy that the FDA finally acted to remove these chemicals from soaps. But I was dismayed to discover at my local drugstore that most products now contain substitutes that may be worse,” said Arlene Blum, PhD, Executive Director of Green Science Policy Institute.

This is why Blum, Sattler, and hundreds of other researchers signed this statement (which you can read here): to tell people they don’t work and to avoid them whenever possible.

“Customers may think added antimicrobials are a way to reduce infections, but in most products there is no evidence that they do,” said Ted Schettler, MD, MPH, Science Director of the Science and Environmental Health Network. In 2016, Dr. Schettler authored a report on antimicrobials in hospital furnishings for the nonprofit Health Care Without Harm.

Seriously, any soap will do just fine. Image via Pixabay.

The problem, or at least a big part of the problem, is that a simple name can be so powerful: antimicrobial. Who doesn’t like that? Who doesn’t want to eliminate germs? What parent wouldn’t opt for an antimicrobial soap, compared to just a soap? But we shouldn’t fall for that. Names can be tricky, and marketing can be even trickier. Don’t fall for that. Trust the scientists, not the marketers.

The statement also includes several recommendations, both for consumers and policy makers, which we’ll present here:

  • Avoid the use of triclosan, triclocarban, and other antimicrobial chemicals except where they provide an evidence-based health benefit (e.g., physician-prescribed toothpaste for treating gum disease) and there is adequate evidence demonstrating they are safe.
  • Where antimicrobials are necessary, use safer alternatives that are not persistent and pose no risk to humans or ecosystems.
  • Label all products containing triclosan, triclocarban, and other antimicrobials, even in cases where no health claims are made.
  • Evaluate the safety of antimicrobials and their transformation products throughout the entire product lifecycle, including manufacture, long-term use, disposal, and environmental release.

The bottom line is pretty simple: wash your hands with water and soap, avoid antimicrobials. Read the labels of products and see what they contain. Don’t fall for an attractive name. Follow the science.

Journal Reference: Rolf U. Haiden et al — The Florence Statement on Triclosan and Triclocarban. DOI:10.1289/EHP1788

The Marangoni Effect – an affair with surface tension

The Marangoni Effect says that fluid will want to flow from areas of lower surface tension to areas of higher surface tension.

Soap has a lower surface tension than Water/ Milk. And as a result, when soap is placed on the surface of a fluid (as it is, in these animations), it wants to flow away to areas of higher surface tension. A more in-depth explanation of the Marangoni effect and surface tension in general can be found a previous ZME Science post.

And this propels the small boat, causes the pepper flakes to spread away, makes the string to expand, and the dye to fan out. It is also responsible for the Tears of Wine phenomenon that you might have already witnessed. : )


PC: Flow Visualization at UC Boulder, source video, MIT, Dan Quinn

Antibacterial soap is no better at killing germs than regular soap

Regular soap is really good at killing bacteria, but most people feel that antibacterial soaps are even better. After all, they’re antibacterial, right? Well, according to a thorough research, that’s not true at all – regular soap works just as good as antibacterial soap.

Image via MSU Today.

The main ingredient that differentiates “antibacterial” soaps is triclosan. Triclosan is an antibacterial and antifungal agent widely used in detergents and soaps, but whose efficacy as an antimicrobial agent and the risk of bacterial resistance remain controversial. Now, a new study published in the Journal of Antimicrobial Chemotherapy found no difference in terms of killing germs between regular soaps and triclosan soaps.

In the study, Min-Suk Rhee and colleagues from Korea University exposed 20 strains of bacteria to the two types of soap – a regular one, and one with 0.3 percent triclosan concentration – the maximum concentration allowed by law. The bacteria was exposed to the soap for 20 seconds, simulating an average hand wash.

The same experiment was repeated on 16 participants, who were asked to wash their hands with the two soaps just as they regularly do. In both cases, there was no noticeable difference.

“Antibacterial activities of triclosan have been well documented. However, its risk remains controversial since various adverse effects have been reported, including allergen, antibiotic resistance, carcinogenic impurities and bioaccumulation,” Rhee says. “Our study indicates there was no significant difference in antiseptic effects” between soaps that contain triclosan and those that don’t.

This comes as triclosan has been under scrutiny for potential health hazards, which include skin rashes, allergies, and “training” drug-resistant bacteria. Whether or not that’s the case, buying triclosan soap when regular soap is just as good is simply not worth the risk.