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How exactly does alcohol solution kill or neutralize viruses?

How exactly does alcohol solution kill or neutralize viruses?


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To reduce the risk of infection by viruses (including 2019-nCoV) the CDC suggests:

  • Wash your hands often with soap and water for at least 20 seconds. Use an alcohol-based hand sanitizer that contains at least 60% alcohol if soap and water are not available.
  • Avoid touching your eyes, nose, and mouth with unwashed hands.
  • Avoid close contact with people who are sick.
  • Stay home when you are sick.
  • Cover your cough or sneeze with a tissue, then throw the tissue in the trash.
  • Clean and disinfect frequently touched objects and surfaces.

To my knowledge most alcohol-based hand sanitizers use ethanol. In clinical settings sometimes isopropanol is also used.

Question: How exactly do alcohols, especially ethanol and isopropanol provide some disinfecting action against viruses? Are the virus particles simply dissolved? What happens?


Alcohols dissolve lipid bilayers

Many viruses have an outer lipid bilayer. Ethanol lyses cells, and in the same fashion damages membrane-bound viruses by rupturing the bilayer (which is made of ethanol-soluble lipids).

Alcohols misfold the protein coats of viruses

Additionally, alcohols denature proteins, which misfold in non-aqueous conditions. Some viral surface proteins are important for adhesion and attachment, and misfolding these renders the virus inactive. The total breakdown of viruses is essentially due to the misfolding of their protein coat (the capsid).

The same goes for bacteria

With the additional effect of dehydrating cells

Alcohols substitute the water contents of a tissue and have been as such used as fixatives. Common laboratory examples include methanol and ethanol.

Typically, 70% (140 proof) ethanol is used for bench wiping to kill or inactivate microbes. This includes viruses.

This is all standard, common, easily and readily accessible knowledge. Here's a bonus source.


A comment on the question suggests that several infectious viruses (including 2019-nCoV) are envelope viruses and that alcohol can "strip away the molecules used for host cell recognition". Viral envelopes (are), typically derived from portions of the host cell membranes.

A key component of these envelopes are of course lipids.

From Antiviral activity of alcohol for surface disinfection:

Antiviral activity and the viral envelope

Because of the structure and composition of the different virus families, viruses react differently to the action of disinfectants. From a disinfectant point of view, the presence or absence of an envelope is the most important trait of a virus. Lipid-enveloped virus families are, generally, susceptible to many disinfectants, alcohols included. The higher the lipid content and the larger the virion itself, the more susceptible the virus is.

Many (but not all) of the so called small 'naked' virus families (e.g. adeno, parvo, picorna viruses causing a.o. poliomyelitis,hepatitis A, hand foot and mouth disease, common cold) that do not possess an envelope are quite resistant to common disin-fectants, alcohols included (6, 7).

Fortunately, the herpes viruses (herpes simplex I and II, 5-8,varicella, Epstein Barr); paramyxo viruses (measles, mumps);retro viruses (HIV, AIDS); hepadna viruses (hepatitis B); coronaviruses (SARS) are lipid-enveloped virus families that are, generally, susceptible to the disinfectant activity of alcohols(5, 8).

5 JuÈlich W-D, v. Rheinbaben F, Steinmann J, Kramer A. On the virucidal efficacy of chemical and physical disinfectants or disinfection procedures. Hyg Med 1993; 18: 303-26.

6 Tyler R, Ayliffe GA, Bradley C. Virucidal activity of dis-infectants: studies with the poliovirus.J Hosp Infect 1990; 15:339-45.

7 Mbithi JN, Springthorpe VS, Sattar SA. Chemical disinfection of hepatitis A virus on environmental surfaces. Appl Environ Microbiol 1990; 56:3601-4.

8 Croughan WS, Behbehani AM. Comparative study of inactivation of herpes simplex virus types 1 and 2 by commonly used antiseptic agents.J Clin Microbiol 1998; 26: 213-5.


New Way to Kill Viruses: Shake Them to Death

Scientists may one day be able to destroy viruses in the same way that opera singers presumably shatter wine glasses. New research mathematically determined the frequencies at which simple viruses could be shaken to death.

"The capsid of a virus is something like the shell of a turtle," said physicist Otto Sankey of Arizona State University. "If the shell can be compromised [by mechanical vibrations], the virus can be inactivated."

Recent experimental evidence has shown that laser pulses tuned to the right frequency can kill certain viruses. However, locating these so-called resonant frequencies is a bit of trial and error.

"Experiments must just try a wide variety of conditions and hope that conditions are found that can lead to success," Sankey told LiveScience.

To expedite this search, Sankey and his student Eric Dykeman have developed a way to calculate the vibrational motion of every atom in a virus shell. From this, they can determine the lowest resonant frequencies.

As an example of their technique, the team modeled the satellite tobacco necrosis virus and found this small virus resonates strongly around 60 Gigahertz (where one Gigahertz is a billion cycles per second), as reported in the Jan. 14 issue of Physical Review Letters.

A virus' death knell

All objects have resonant frequencies at which they naturally oscillate. Pluck a guitar string and it will vibrate at a resonant frequency.

But resonating can get out of control. A famous example is the Tacoma Narrows Bridge, which warped and finally collapsed in 1940 due to a wind that rocked the bridge back and forth at one of its resonant frequencies.

Viruses are susceptible to the same kind of mechanical excitation. An experimental group led by K. T. Tsen from Arizona State University have recently shown that pulses of laser light can induce destructive vibrations in virus shells.

"The idea is that the time that the pulse is on is about a quarter of a period of a vibration," Sankey said. "Like pushing a child on a swing from rest, one impulsive push gets the virus shaking."

It is difficult to calculate what sort of push will kill a virus, since there can be millions of atoms in its shell structure. A direct computation of each atom's movements would take several hundred thousand Gigabytes of computer memory, Sankey explained. He and Dykeman have found a method to calculate the resonant frequencies with much less memory.

In practice

The team plans to use their technique to study other, more complicated viruses. However, it is still a long way from using this to neutralize the viruses in infected people.

One challenge is that laser light cannot penetrate the skin very deeply. But Sankey imagines that a patient might be hooked up to a dialysis-like machine that cycles blood through a tube where it can be hit with a laser. Or perhaps, ultrasound can be used instead of lasers.

These treatments would presumably be safer for patients than many antiviral drugs that can have terrible side-effects. Normal cells should not be affected by the virus-killing lasers or sound waves because they have resonant frequencies much lower than those of viruses, Sankey said.

Moreover, it is unlikely that viruses will develop resistance to mechanical shaking, as they do to drugs.

"This is such a new field, and there are so few experiments, that the science has not yet had sufficient time to prove itself," Sankey said. "We remain hopeful but remain skeptical at the same time."


How does hand sanitizer work?

The key ingredient in most hand sanitizers is alcohol. Chemically speaking, alcohols are organic molecules made of carbon, oxygen and hydrogen. Ethanol is the chemical in alcoholic drinks and is the chemical most people are thinking of when they say alcohol. Propanol and isopropanol (isopropyl alcohol) are two other alcohols that are common in disinfectants because they're highly soluble in water, just like ethanol.

Alcohols destroy disease-causing agents, or pathogens, by breaking apart proteins, splitting cells into pieces or messing with a cell's metabolism, according to a 2014 review published in the journal Clinical Microbiology Reviews. Solutions with as little as 30% alcohol have some pathogen-killing ability, and the effectiveness increases with increasing alcohol concentration. Studies have shown that alcohol kills a more broad variety of bacteria and viruses when the concentration exceeds 60%, and it works faster as the concentration increases. But the effectiveness of alcohol seems to top out at about a 90-95% concentration.

Another strength of alcohol is that the bacteria it kills don't develop a resistance to it, so alcohol doesn't lose effectiveness with continued use.

According to the 2014 review, ethanol is so powerful that a few studies have found that in high concentrations, it's better at getting rid of three species of disease-causing bacteria &mdash Escherichia coli, Serratia marcescens and Staphylococcus saprophyticus &mdash compared with washing hands with regular or antibacterial soap.

But alcohol 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, the Centers for Disease Control and Prevention says. Hand sanitizers also don't remove harmful chemicals like pesticides or heavy metals, nor does hand sanitizer work well on especially dirty or greasy hands. So, soap and water still win the contest overall.

There are a few small-scale studies demonstrating that an alcohol-free hand sanitizer containing benzalkonium chloride as the active ingredient, at a concentration of 0.13%, is just as effective and even more effective than alcohol at getting rid of bacteria. The alcohol-free hand sanitizer that was tested was called HandClens, and the scientists who conducted the research on it worked for the now-closed laboratory that developed the product. That doesn't mean benzalkonium chloride isn't effective, but there doesn't seem to be independent research to suggest that it's better than alcohol. Plus, benzalkonium chloride might be harmful for some individuals, especially at higher concentrations, according to the Hazardous Substances Database.

According to the CDC, hand sanitizer without alcohol may not kill as many germs and may only reduce the growth of germs rather than killing them outright. The CDC recommends hand sanitizers with at least 60% alcohol in them for maximum effectiveness.


As BAC Increases—So Do the Risks

As blood alcohol concentration (BAC) increases, so does the effect of alcohol—as well as the risk of harm. Even small increases in BAC can decrease motor coordination, make a person feel sick, and cloud judgment. This can increase an individual’s risk of being injured from falls or car crashes, experiencing acts of violence, and engaging in unprotected or unintended sex. When BAC reaches high levels, blackouts (gaps in memory), loss of consciousness (passing out), and death can occur.

BAC can continue to rise even when a person stops drinking or is unconscious. Alcohol in the stomach and intestine continues to enter the bloodstream and circulate throughout the body.

It is dangerous to assume that an unconscious person will be fine by sleeping it off. One potential danger of alcohol overdose is choking on one’s own vomit. Alcohol at very high levels can hinder signals in the brain that control automatic responses such as the gag reflex. With no gag reflex, a person who drinks to the point of passing out is in danger of choking on his or her vomit and dying from a lack of oxygen (i.e., asphyxiation). Even if the person survives, an alcohol overdose like this can lead to long-lasting brain damage.

Critical Signs and Symptoms of an Alcohol Overdose

  • Mental confusion, stupor
  • Difficulty remaining conscious, or inability to wake up
  • Vomiting
  • Seizures
  • Slow breathing (fewer than 8 breaths per minute)
  • Irregular breathing (10 seconds or more between breaths)
  • Slow heart rate
  • Clammy skin
  • Dulled responses, such as no gag reflex (which prevents choking)
  • Extremely low body temperature, bluish skin color, or paleness

Antiseptic vs. antibacterial mouthwashes

What is the significant difference between a product that is antiseptic and one that is antibacterial? All of the antiseptic mouthwashes I find have a great amount of alcohol in them. This can be very irritating to the mouth. I have found one that is alcohol free, but it says it is antibacterial.

Mouthwashes can help prevent cavitities, slow the buildup of plaque, and fight bad breath. Antibacterial products kill bacteria, or hinder their reproduction. Antiseptic substances inhibit the growth and reproduction of many microorganisms, including bacteria, as well as fungi, protozoa, and viruses.

A mouthwash that kills or reduces the number of bacteria in one's mouth can decrease the production of the sulfur compounds that are one cause of bad breath. For other causes, see More on bad breath (halitosis) in the Go Ask Alice! archive. Some mouthwashes contain ingredients, such as cetylpyridinium chloride (CPC), zinc chloride, or chlorhexidine, which may directly neutralize these sulfur compounds.

The greatest difference between antibacterial and antiseptic mouthwashes is exactly what you pointed out: most antiseptic mouthwashes contain a significant amount of alcohol, often about 25 percent. Some people, yourself included, find alcohol irritating. Alcohol is a desiccant, meaning it tends to dry things out, including the lining of your mouth. Having a dry mouth could actually aggravate bad breath. In fact, most dentists will tell you that the greatest preventative measure against bad breath is to drink plenty of water to promote saliva production in the mouth, as saliva itself has natural antibacterial properties. Happy rinsing!


1 Answer 1

A more recent study (also published by the CDC) seems to indicate that 30% might be a good enough concentration against SARS-CoV-2:

[Figure legend:] Effect of commercially available alcohols in inactivating SARS-CoV-2. The means of 3 independent experiments with SDs (error bars) are shown. A) Results for ethanol. B) Results for 2-propanol. Dark gray bar indicates cytotoxic effects, calculated analogous to virus infectivity. Dashed line represents limit of detection. Reduction factors are included above the bar. The biocide concentrations ranged from 0–80% with an exposure time of 30 s. Viral titers are displayed as TCID50/mL values. LLOQ, lower limit of quantification SARS-CoV-2, severe acute respiratory syndrome coronavirus 2 TCID50/mL, 50% tissue culture infectious dose.

[. ] Conclusions: [. ] ethanol and 2-propanol were efficient in inactivating the virus in 30 s at a concentration of >30% (vol/vol). Alcohol constitutes the basis for many hand rubs routinely used in healthcare settings. One caveat of this study is the defined inactivation time of exactly 30 s, which is the time recommended but not routinely performed in practice.

Having said this, antiseptics and disinfectants (in general) are binned in roughly 3 categories based on what they can deal with. Mycobacteria (e.g. tuberculosis) and bacterial spores are a harder (and respectively a lot harder) to inactivate/kill than viruses. (Some antiseptics were even contaminated with mycobacteria.) So (besides possible non-compliance with the recommended use/rubbing time) this is a good reason to demand greater alcohol concentration in general-purpose alcohol-based antiseptics.

Furthermore, even just a far as alcohol effectiveness against viruses is concerned, a 2019 Japanese study of influenza A virus (IAV) inactivation by ethanol found that [non-dry] mucus constituted an extra protective layer for the virus (besides its own envelope), slowing the effect of ethanol-based disinfectants (EBDs) about eight times:

Our clinical study showed that EBD effectiveness against IAV in mucus was extremely reduced compared to IAV in saline. IAV in mucus remained active despite 120 s of AHR [antiseptic hand rubbing] however, IAV in saline was completely inactivated within 30 s. Due to the low rate of diffusion/convection because of the physical properties of mucus as a hydrogel, the time required for the ethanol concentration to reach an IAV inactivation level and thus for EBDs to completely inactivate IAV was approximately eight times longer in mucus than in saline. On the other hand, AHR inactivated IAV in mucus within 30 s when the mucus dried completely because the hydrogel characteristics were lost.

(30s is the hand-rubbing typically recommended for antiseptics when used as hand sanitizers.)


All the Ways to Kill a Coronavirus (So Far)

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The race is on to find a cure for Covid-19. Researchers are testing new vaccines, resurrecting old drugs, and repurposing treatments originally developed for other diseases. Things are moving fast by the time you read this, the situation may have changed (for the better, we hope). So how are scientists thinking they'll fend off this tiny viral adversary? Here are a few lines of attack.

Each particle of the new virus, SARS-CoV-2, is studded with spikes, which allow it to attach itself to a human cell, poke a hole, and burrow inside. Like the germ that caused the SARS epidemic in 2003, it sticks to a protein on human cells called ACE2, which is especially prevalent in the lungs and small intestine. (SARS-CoV-2 is at least 10 times stickier than its cousin, which may account for its rapid spread.) One way to stop the invader is to keep it from attaching in the first place. This is what your immune system tries to do—it sends out antibodies that gum up the spikes so the virus can't stick to ACE2. But there are other ways of achieving the same effect.

1. Make a vaccine. For powerful, long-lasting immunity, a so-called live attenuated vaccine is the gold standard. It contains a defanged version of the virus that your immune system can use for target practice—but it can also cause infection. That's why many researchers are working on vaccines that contain not the whole virus but just the outer spikes. Mixed with immune-boosting molecules called adjuvants, they'll elicit a safe antibody response.

2. Take antibody-rich blood plasma from people who have survived Covid-19 and inject it into newly infected or at-risk patients. Plasma won't teach the body how to fend off the virus, and one injection won't last forever—but it could be a good way to prepare health workers before they head to a hot spot.

3. Flood the zone with decoys—synthetic molecules that look like ACE2 and trick the virus into binding with them instead, protecting lung cells from damage.

4. Invent drugs that hinder ACE2 from binding with the virus. In theory, these compounds would work on both SARS and Covid-19, stopping the viruses from sticking to cells. But ACE2 plays a number of other roles throughout the body it helps regulate blood pressure, kidney function, and even fertility. Messing with it could have dangerous consequences.

All viruses wear heavy-duty protein coats to protect their precious genetic material from the elements. The new coronavirus sports an extra outer layer of fatty molecules. That's great news for humans, because it's easy to tear open with soap or alcohol-based disinfectants. (Soap works best, and you don't need to bother with the antibacterial stuff.) Without its fatty layer, the virus dies. Wipe it away or wash it down the drain.


Interviewer: Doing some spring cleaning and you come across some mouse droppings? Well, stop and listen to this podcast first before you do any more cleaning. That's next on The Scope.

Announcer: Health tips, medical news, research, and more for a happier, healthier life. From University of Utah Health Sciences, this is The Scope.

Interviewer: If you're doing some spring cleaning, maybe cleaning out the garage or an old attic, and you see some mouse or some sort of droppings, is that a concern? It turns out yes, it is, and there's a procedure you should go through if you do see that before you continue cleaning. Dr. Troy Madsen is an emergency room physician at University of Utah Health. What's the main concern here?

Dr. Madsen: The big concern here is something called hantavirus. This is a virus that mice carry. It's actually endemic to the four corners region, so southeastern Utah, but we've certainly seen cases in Salt Lake. There was a big outbreak of this virus at Yosemite several years ago. This is a virus that mice carry in their urine.

So the way people catch this virus is they're cleaning mouse droppings, they see some droppings, they sweep it up, sweep it into a dust pan. As they're sweeping, usually, where there are mouse droppings, there's also mouse urine, it aerosolizes this urine, this dry urine, kind of kicks it up into the air, they breathe it into their lungs, and then it can cause an extremely severe lung infection.

Very fatal, at least half of people who get this infection die from it. It's a bad thing to have. I personally know someone who had it who was cleaning his garage, caught the virus after cleaning. It's a big concern. Then you may ask, "Why is it a big concern this year in particular?" Because it's been a very, very wet winter, and when we have wet winters, the rodent population explodes.

This is exactly what happened at Yosemite several years ago when there was a big outbreak there. You get more mice around carrying this virus, more potential for exposure for humans, so we could potentially see cases of these.

Interviewer: If you see mouse droppings, that's the first hint that you need to do what we're about to talk about, is what do you about it, because you want to clean that mess up.

Dr. Madsen: Exactly. You're not just going to leave the mouse droppings. You've got to do something about it. Take some water, pour some bleach in it. It's kind of a 1 to 10 ratio. If you have a bucket of water, just get some bleach in that. You can then use that water and bleach in a spray bottle or pour it on the mouse droppings some way where you're getting the bleach on there, getting that area wet.

The reason this works is because you've got the bleach on there that's killing the virus. Then you've also got something wet on there. So when you wipe that up, it's not creating an aerosol. It's not creating something out of that dry urine that it gets in the air and you breathe in your lungs. That's the biggest thing for prevention.

Interviewer: So then you just target where you see the mouse droppings. You don't have to spray the solution on every surface in wherever you happen to be working?

Dr. Madsen: Exactly. If you're cleaning a garage, you figure if you're trying to get this solution all over, it's just not practical. Usually, where the mice have their droppings, that's where the urine is. My recommendation would be to have a spray bottle with you with the solution in it. If you're cleaning the garage, spray five or six squirts on that area. Let it sit for 5 to 10 minutes, then wipe it up, and you should be good at that point.

Interviewer: Okay, and wear a mask at the same time?

Interviewer: Would a mask alone stop it?

Dr. Madsen: Great question. I don't have a great answer. I think a mask would definitely help, would probably prevent it. I would still take the precautions with the solution though.

Interviewer: Let's say somebody didn't catch this in time, and now they're concerned that they have hantavirus. What are the symptoms?

Dr. Madsen: It's a little bit of a challenge because it probably feels at first like a bad cold, but then it progresses very rapidly to where you're having very significant difficulty breathing. It's one of those things where if you really have it, you'll probably know you have it, and you'll probably know pretty quickly.

Interviewer: A cold following some sort of a cleaning job in a place where this could have happened would be your first hint, and then go to the ER?

Dr. Madsen: Exactly. I would go to the ER for this. I don't want you to rush to the ER if you've been cleaning and then you get a little bit . . . some sniffles, but it's one of those things where it's something you would go to the ER for, anyway, because you would feel so sick and have so much trouble breathing. Even if you hadn't been cleaning, you would say, "Something's not right here."

Interviewer: Then what do you do to treat it?

Dr. Madsen: That's the challenge with it. Really, the treatment for it in the hospital is supportive care. We're helping people get through it while, hopefully, their body fights this off. Often, that means breathing for them, putting a tube in, and putting them on a ventilator to get them through this. In severe cases, that's what we have to do, but it's a challenge to treat.

Interviewer: So well worth avoiding?

Dr. Madsen: Absolutely. Try to avoid it.

Announcer: Want The Scope delivered straight to your inbox? Enter your email address at thescoperadio.com and click "Sign Me Up" for updates of our latest episodes. The Scope Radio is a production of University of Utah Health Sciences.

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Moist heat causes destruction of micro- organisms by denaturation of macromolecules, primarily proteins. Autoclaving (pressure cooking) is a very common method for moist sterilization. It is effective in killing fungi, bacteria, spores, and viruses but does not necessarily eliminate prions. When sterilizing in this way, samples are placed into a steam chamber. The chamber is closed and heated so that steam forces air out of the vents or exhausts. Pressure is then applied so that the interior temperature reaches 121°C. This temperature is maintained for between 15 and 30 minutes. This elevated temperature and pressure is sufficient to sterilize samples of any commonly encountered microbes or spores. The chamber is then allowed to cool slowly or by passive heat dissipation.

Pressure sterilization is the prevailing method used for medical sterilization of heat-resistant tools. It is also used for sterilization of materials for microbiology and other fields calling for aseptic technique. To facilitate efficient sterilization by steam and pressure, there are several methods of verification and indication used these include color-changing indicator tapes and biological indicators. For any method of moist heat sterilization, it is common to use biological indicators as a means of validation and confirmation. When using biological indicators, samples containing spores of heat-resistant microbes such as Geobacillus stearothermophilis are sterilized alongside a standard load, and are then incubated in sterile media (often contained within the sample in a glass ampoule to be broken after sterilization). A color change in the media (indicating acid production by bacteria requires the medium to be formulated for this purpose) or the appearance of turbidity (cloudiness indicating light scattering by bacterial cells) indicates that sterilization was not achieved and the sterilization cycle may need revision or improvement. Other moist methods are boiling samples for certain period of time and Tyndallisation. Boiling is not efficient in eliminating spores. Tyndallisation inactivates spores as well, but is a more lengthy process.

Figure: Autoclave: Large autoclave used for moist sterilization of media and equipment


First Step: Use Soap

The CDC has approved a variety of disinfectants to combat coronavirus, including store-bought products and those made from common household goods, like bleach. But, let’s start with the basics: soap and water.

How to Prepare Your Home for Coronavirus

A thorough cleaning with good ol’ soap and water is the first step to sanitizing your home against coronavirus. This is because grime and other substances can neutralize the active ingredients in disinfectants to be used afterward, rendering them ineffective.


FACT: Exposing yourself to the sun or temperatures higher than 25°C DOES NOT protect you from COVID-19

You can catch COVID-19, no matter how sunny or hot the weather is. Countries with hot weather have reported cases of COVID-19. To protect yourself, make sure you clean your hands frequently and thoroughly and avoid touching your eyes, mouth, and nose.