Soap vs hand sanitizer...pero, por qué no los dos?
So last time on the Quarantine Chronicles, we talked a little bit about the structure of SARS-CoV-19 and how that allows the virus to jump between different species. Considering how people have been hoarding Purell like it is the end-of-days (and I assure you that although we have lost every major sports league season, for the time being, we will survive), I think it's worth digging into the question of soap vs hand sanitizer, and other disinfectants.
Storytime: flashback to my Sophomore year of college. I sat in the front row of my Intro to Medical Microbiology class (shoutout to Dr. Cramer who in part inspired this blog) and watched one of my closest friends wipe down a chair with a Lysol wipe for 10 minutes in front of the lecture hall of some 200 undergrads. The point she was trying to make (thanks Ryan for being a trooper!), was that although disinfecting wipes claim to "eliminate 99.99% of viruses and bacteria", they are only effective if used properly. And unless you wipe down your surfaces for 10 minutes, I can guarantee that you have been doing it wrong. Both Dr. Cramer and the Centers for Disease Control and Prevention stated that "disinfection usually requires that the product remains on the surface for a certain period of time"...or as illustrated in lecture, that the surface must be visibly wet for 10 whole minutes. If you read the fine print of your Lysol wipes, the label even specifies 4 minutes. Do it! I dare you!
The length of this video is longer than you wipe down your surfaces and it isn't even enough. Also, hello Moonlight Dance Crew hoodie!
The active ingredient in these wipes are quaternary ammonium compounds ("quats" for short) which have been found to irritate the skin, lungs, and negatively affect reproductive health. They are effective when used properly, but don't go wiping your hands with them out of hysteria. Wipe down surfaces (ahem, like your grimy phone) as directed and rinse off the residue from your skin to prevent irritation.
As mentioned before, fomites aren't our biggest concern for COVID-19. Good old 10th-grade science taught us that similar molecules interact more strongly with each other than dissimilar ones. Example: the phospholipid bilayer! Polar heads would rather assemble together and tuck away the hydrophobic tails.
A Twitter thread by Dr. Palli Thordarson of the UNSW Sydney School of Chemistry does a great job of digging into the ~supramolecular chemistry~ behind this debate with respect to responding to COVID-19.
SARS-CoV-19 is held together by hydrogen bonds and hydrophilic interactions and when it interacts with similar surfaces like fabric and skin, hydrogen bonds can form between these surfaces and the virus. When the virus interacts with more dissimilar surfaces like porcelain or steel, the virus does not form those bonds and remains stable for some time on those surfaces. If someone coughs on their hand, the virus binds to the skin's surface and when people shake hands then the viruses transfers to another person. Hence, person-to-person transmission is the biggest issue, so let's talk about getting our hands dirty and how to appropriately clean them.
For starters, it is important to note that the type of virus also determines its ability to be infectious and what agents we should use to effectively destroy them. The general anatomy of a virus includes nucleic acids that make up the genes of the virus (DNA or RNA) and a protein capsid that holds the nucleic acids. Building on this basic anatomy, viruses can either be naked (just the genetic material and the protein coat) or enveloped by a lipid bilayer. This seemingly simple difference has a rather significant impact on the virus' ability to survive. Naked viruses are more resistant to disinfectants because the outermost protein capsid can withstand detergents and mechanical damage. Whereas lucky for us (I mean, comparably), the COVID-19 virus is enveloped. This outer lipid layer is much more susceptible to detergents and mechanical damage. If we can destroy this outer layer, then the virus is not infectious anymore.
Note: The image below and information supporting the text above can be referenced to McGraw-Hill.
This interference with the virus' lipid envelope is how alcohol and alcohol-based hand sanitizers work on the virus. Again, no envelope = no infection. Hand sanitizers that are more than 60% alcohol will effectively kill the virus. In this case, a passing percentage does the trick. Before you try to steal your lab's giant container of 100% alcohol, know that water is necessary to catalyze the reaction that allows alcohol to denature the virus' structure. AND, before you try to make your own home-made concoction of hand sanitizer with the leftover vodka from the Spring Break party that never happened because of quarantines...know that 80 proof vodka is only 40% alcohol and will NOT save you from COVID-19. (Don't drink it either! The details of that are an entire post on its own.)
Going back to the point made earlier, surfaces need to remain wet for a period of time in order for the necessary molecular reactions to occur. Alcohol is volatile and evaporates quickly, which also poses another challenge for disinfecting. Additionally, depending on the family of the virus, concentrations between 60% and 90% alcohol will be specific to different families.
So, hand sanitizers are effective and a great idea when you can't get to a sink. However, hand washing WITH SOAP (none of that 3-second rinse after you use the toilet stuff!) is more effective so do so as often as you can.
What is so great about soap? Let's revisit the reference to similar molecules interacting from above.
Amphiphiles in soap are fat-like substances that are structurally similar to the lipids in the viral envelope. These molecules can compete with the lipids in the virus membrane and also outcompetes the interactions between the virus and the skin so the virus cannot attach to the organic surface. Alcohol is capable of dissolving the viral lipid membrane at the appropriate concentration but is overall not as effective as soap in disrupting these molecular interactions.
So there you have it! As Dr. Thordarson writes, COVID-19 is a "nano-sized grease ball" and regardless of the size of the viral particles, soap is incredibly effective in pulling-apart these grease balls.
In summary:
Lysol wipes with their fancy "quats" kill viruses but only when used properly and they should not be used on skin.
Alcohol and alcohol-based hand sanitizers are great for when you can't get to a sink but can fail if the concentration is too low (or high), if your hands are greasy, and if you get sweaty palms. (Don't go on that awkward sweat-inducing date with someone who may be infected.)
Soap is essentially a fail-safe option, provided that you scrub into the nooks and crannies of your skin for 20 seconds (even if it isn't specifically antibacterial!).
I know that the world feels like it's coming to an end and that the current lack of an available vaccine or antiviral medication seems discouraging. However, the science behind public health messaging pushing hand-washing doesn't lie.
Keep calm, and wash on (with soap)!
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