1. Unlike non-enveloped viruses, enveloped viruses can be killed with soap, alcohol, etc. Why?

  2. Why does just having an envelope make it susceptible to soap and alcohol?

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    $\begingroup$ (+1) Re: "Why does just having an envelope makes it susceptible to soap and alcohol?": We often describe humans as "two-legged" and cats as "four-legged", but in the parallel universe where humans are "handed" and cats are "non-handed", someone is asking why "just having hands" makes humans so much more susceptible to loss of balance. $\endgroup$ – ruakh Aug 30 at 5:57
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    $\begingroup$ different but related: How exactly does alcohol solution kill or neutralize viruses? $\endgroup$ – uhoh Aug 30 at 9:08
  • $\begingroup$ @Alex Reynolds do you know how soap and alcohol affect other viruses and or bacteria? does it make sense to only use soap or is a good alcoholic desinfectant still better? $\endgroup$ – Mike Bader Aug 31 at 20:48
  • $\begingroup$ If the CDC can still be trusted any longer, it indicates that washing your hands with soap and water is a good way to stay healthy and avoid a number of bugs, and that it does better at that job than alcohol-based hand sanitizer: cdc.gov/handwashing/show-me-the-science-hand-sanitizer.html $\endgroup$ – Alex Reynolds Aug 31 at 21:25

Soap molecules are amphiphilic. This means they have parts which are hydrophilic (water-loving, or "polar") and parts which are hydrophobic (water-avoiding, or "non-polar").

Fat molecules are non-polar. They avoid water. This is why a mixture of oil and water will separate into layers. In this mix, oil molecules prefer to hang around other oil molecules, and water molecules prefer to hang around other water molecules. Soap "likes" both oil and water, so it can be used for cleaning, by helping dissolve this mixture. (For a similar reason, this is why vinegar is used to dissolve or emulsify oil in salad dressings.)

The coat of an enveloped virus is made up of layer of phospholipid molecules and proteins. Phospholipid molecules are similar to detergents, made up of polar and non-polar ends. These lipids arrange themselves into a two-layered sandwich called a "bilayer". The polar ends of this sandwich are the "bread", while the fatty non-polar ends are the "filling".

Detergents can help disturb this by pulling or dissolving out phospholipids from the virus coat to form micelles, tiny bubbles of fat and soap that can be washed away. This puts holes in the virus coat and helps dissolve it.

The insides of the enveloped virus particle cannot infect directly and must rely on its envelope to get into and infect a cell, so breaking down the coat inactivates (or "kills") the virus.

Alcohols are also amphiphilic. There are many different alcohols, but they all have a hydroxy group at one end, which is polar, and a saturated or partially-saturated carbon chain on the other end, which is non-polar. Like detergents, this property allows an alcohol — at a sufficient concentration — to disturb and break down the virus envelope phospholipid bilayer, inactivating it.

Non-enveloped viruses lack this phospholipid bilayer coating and are instead protected by a protein capsid. The proteins in a capsid will not dissolve with detergents, but they can be attacked with other disinfectants that chemically denature the proteins. Examples of such disinfectants are chlorine (bleach), iodine, peroxides, etc.

Just as soap can put holes into the phospholipid coating around enveloped viruses, destabilizing them, denaturing agents change the structure of proteins that protect non-enveloped viruses, also destabilizing the capsid. If the capsid proteins are damaged sufficiently, the virus particle is not able to infect a cell and so is deactivated.

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    $\begingroup$ Great answer, but a minor organic chemistry quibble - alcohols are defined by having a hydroxy group attached to a saturated $\alpha$-carbon, but further down the chain, any existing carbons don't necessarily need to be completely saturated. $\endgroup$ – MattDMo Aug 29 at 19:31
  • $\begingroup$ Small correction: enveloped viruses also have a capsid. $\endgroup$ – gardenhead Aug 29 at 21:58
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    $\begingroup$ Feel free to add a better answer to How exactly does alcohol solution kill or neutralize viruses? or we can consider closing that as duplicate of this question. I find this answer much more informative, and you've covered alcohol here to some extent. $\endgroup$ – uhoh Aug 30 at 9:09
  • $\begingroup$ I don't mind; whatever you prefer. $\endgroup$ – Alex Reynolds Aug 30 at 20:05
  • $\begingroup$ Is there a difference here between soap and products branded 'soap free wash/cleanser'? (Like Eucerin, Cetaphil, Neutrogena, DermaVeen etc.) $\endgroup$ – Laura Sep 1 at 4:58

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