Hand washing and why it’s effective against microbes

 

I want to start out by stating I’m not a virologist, I am a chemistry graduate student studying cellular signaling in bacteria. I’m also learning a lot of this as I go, but I’ve noticed that there’s a lot of misinformation out there so I want to keep everyone up to date on the facts. If there’s something I should edit or if there’s more info you’d like to know, just ask!

 

So to tackle why hand washing is effective let’s first start at the basics of what a virus is and how it works.

What is a virus?

A virus is tiny. They are in the nanometer range. To put that in perspective they are smaller than the mitochondria which is a cellular component in some eukaryotic cells.

Because of their small size you need a specialized microscope to view them; the regular microscopes in most teaching labs will not let you see a virus. This microscope is called an electron microscope and uses electrons as the light source. From electron microscopy we can get images similar to the ones pictured below which show what a few different viruses look like.

Why are these images are in black and white? With electron microscopy you lose color, but these images allow us to create 3D renderings of what the virus would look like.

The CDC, as well as other organizations, have some 3D models of the coronavirus. These renderings are useful because they allow scientists to understand how different parts of the virus functions and thus how the virus itself functions.

Background on coronaviruses

Those red spikes or crowns are what the coronavirus is named after. Most coronaviruses are zootonic in nature, meaning that they can spread between animals and people. Coronaviruses cause respiratory tract infections in humans and while most cases are mild, like the common cold, some coronaviruses can be lethal like SARS (Severe Acute Respiratory Syndrome) or MERS (Middle East Respiratory Syndrome). COVID19 is considered novel because a virus with that sequence wasn’t known before December 2019. Currently the cause of COVID-19 is unknown, but it is thought to have originated at a fish market in Wuhan, China. The name for the virus is now SARS-CoV-2 and the disease is COVID-19 or Corona virus disease-19.

What parts make up a virus and how do they replicate?

So not only are viruses tiny, but they’re so simple that they can’t reproduce on their own. A virus is made up of 3 main things, genetic material (either RNA or DNA), proteins, and lipids. The relevant one is lipids, they are fatty molecules that make up the protective envelope of some viruses including SARS-CoV-2.

Viruses replicate by invading a host cell. Once they’ve invaded, they will hijack the host’s cellular machinery and use it to replicate their own genetic material. So now the host is making viral RNA or DNA, viral proteins, and viral lipids. These components will self-assemble in the host and eventually there will be so many viruses that the host cell will explode, allowing the virus to start infecting new cells in the host and repeating the process.

How do viruses spread and how long do they live?

Viruses can spread through many ways such as bites of infected animals, mosquitoes, and bodily fluids such as blood. SARS-CoV-2 is thought to spread through nasal fluids when sneezing and coughing. In an infected individual, these droplets will contain viruses that can potentially invade a new host. If you are sick, health officials recommend you wear a face mask to prevent spread of your nasal fluids. However, if you are a healthy individual a face mask does not help much because you are likely to touch surfaces containing contagions and if you mess with the face mask, you will introduce those contagions to your face and thus increasing your likelihood of falling ill.

Because viruses need a host to survive, their lifespans are typically shorter. For instance, the flu can last on surfaces for about 48 hours while HIV will only survive 1-2 hours outside of bodily fluids.

Right now SARS-CoV-2 is thought to live up to 3 days on surfaces, however this answer may change as more research is completed and peer reviewed. The good news though is that most coronaviruses can be removed by household disinfectants like ethanol, hydrogen peroxide, and bleach. When using these materials you want to make sure you’re using the right amounts.

For ethanol based products, you want 60-70% ethanol. While it seems like 100% ethanol would be more effective, you need water to actually kill the cells. The way ethanol works is by attacking the lipids in the protective outer envelope and poking holes that allow water to come in. Water can then flood the cell, causing the cell to burst and killing them. On the other hand, 100% ethanol doesn’t work for two reasons, it will simply surround the cell and attack the outer envelope, but instead of poking holes, the envelope will bunch up preventing ethanol from getting into the cells and because it’s pure ethanol instead of staying around the ethanol will just evaporate. High concentrations will definitely still inactivate the microbes, but they will not kill them.

Hydrogen peroxide and bleach, on the other hand, work as oxidizing agents. If you remember your general chemistry this means, it’s an electron acceptor. This means that it will eagerly take electrons from the surfaces (or microbes) that you spray it on. However as oxidizing agents, they are not microbe specific: you can use hydrogen peroxide and bleach to disinfect surfaces, but please do not use it on your skin because it will also kill off your own cells.

There’s no hand sanitizer, should I make my own?

While there are many recipes floating around for how to make your own hand sanitizer, I recommend against it because most OTC alcohol isn’t pure alcohol (usually ranges from 91-99%) so you can’t get to the right concentration easily. Like I mentioned earlier, higher ethanol concentration will not increase antimicrobial activity. If you make your own hand sanitizer that is too high in alcohol it will cause your hands to crack or even bleed which will actually make you more susceptible to microbial infections!

So what exactly is soap and why is it so effective?

First let’s talk about soap. How is soap made? There are hundreds if not thousands of recipes on how to make soap at home, but if you look at the ingredients you need two main things. You need some sort of fat and some sort of basic solution (like lye or sodium hydroxide). On its own lye is harmful and can cause chemical burns, be careful when using it. But in the soap making process the fats and lye will begin to saponify aka the lye and fat will make an exothermic solution, releasing heat and creating soap and glycerin. Soaps are often made with extra fats compared to the lye so the finished product will contain no sodium hydroxide and will therefore not be irritating to the skin.

The fats in the soap are what makes it so effective. The fats allow soap to be both hydrophobic (water hating) and hydrophilic (water loving). What does that actually mean? Soap loves both water and fats and will readily mix with either. Don’t believe me? Try this experiment, in a bottle or glass add some water and some vegetable oil. No matter how hard you try to mix or shake them they will always form two distinct layers. Now add a few drops of soap (doesn’t matter what kind) and try mixing again, now instead of two clear layers, you’ll see that both layers are slightly cloudy. This is because the soap is allowing the oil and water to mix together. If you’re having trouble seeing the difference, try adding a few drops of food coloring to the water!

So now that we know how soap works, how does it help clean your hands? Basically, most of the dirt and food on your hands is also made up of fats.  The hydrophobic tails on the soap molecules will bind to the fats on your hands and trap them inside. The hydrophilic head loves the water and allows the fat contained particle to be washed off your hand. Think of when you have a really dirty pan: you usually use soap and hot water and scrub to remove the grime and it doesn’t happen instantly. It takes some time to clean off all the dirt. The same principle applies to your hands; when you use hot water and soap you can remove the dirt on your hands. And you want to scrub like you’re cleaning a pan – your hand is full of many crevices so you want to take your time to make sure you hit every nook and cranny that dirt can be in.

How does this apply to contagions like viruses and bacteria?

So this makes sense it terms of food, but how does soap help remove bacteria and viruses?

Remember how we talked about that lipid bilayer? The lipid bilayer is on the outside of most viruses and bacteria and it protects the cells.  Unfortunately -for them- the same lipids that protect microbes are their weakest links. The soap particles will be attracted to the lipids in the envelope and will compete with them. This will break up the envelope and allow the virus to be washed off.  If you wash your hands properly and for the recommended time (approximately 20 seconds) you will be able to remove most microbes.

While you can’t really grow viruses in petri dishes, you can grow bacteria. I did a quick experiment showing the effectiveness of soap on bacteria. Since soap works on viruses in the same way it works on bacteria (by attacking the lipid bilayer), rest assured that if you are washing your hands properly you are also removing viruses from your hands.

What you see on these plates is that my hands have tons of bacteria before I wash them. To be fair, I hadn’t washed them in a while! The second picture is me washing my hands with just hot water, no soap no scrubbing, most of the bacteria are still there so even though hot water does kill microbes, it’s not enough. Then I washed my hands with scrubbing for 10 seconds with Softsoap: there’s still bacteria but if you look closely, I did manage to remove some. Finally, I washed my hands for 30 seconds with scrubbing and voila! Most of the bacteria are gone!

And remember, you don’t need fancy or even antibacterial soap! The main agent is soap that makes it useful is the fatty acid loving tails. So even if the market is out of antibacterial soap, the cheap old stuff will work just as well.

Follow WHO and CDC recommendations to stay safe during the coronavirus pandemic. This includes, staying home when you’re sick, practice social distancing (stay 6-10 feet away from people), disinfect surfaces, and avoid touching your face before washing your hands.