Covid-19 and hand hygiene
Monday, May 4th, 2020
Should we use an alcohol-based handrub or a cleanser?
Here’s a bit of chemistry to understand how we can follow Department of Health guidelines but still protect our skin barrier.
In this unprecedented moment in history in which the COVID-19 pandemic is changing the way we live our lives, good hygiene is one of the most important precautions we can take to stop the spread of the virus.
The recommendation to wash our hands frequently has led to a general scramble for alcohol-based handrubs, which have become like gold dust for many.
Alcohol-based handrubs are commonly perceived as being stronger and more effective than washing hands because they are often recommended to prevent bacterial infections.
But do we really need to disinfect our hands to make a virus inactive?
Chemistry can help us understand…
How do cleansers act?
Palli Thordarson (Professor of Chemistry at New South Wales University in Sydney) conveniently explained that from a physical and chemical point of view, the structure of coronaviruses1 is a self-assembled nanoparticle.
It has a lipid bilayer on the outside that envelops the “active” part of the virus, which is made up of RNA and proteins: they are hydrophilic molecules.
This structure with lipophilic and hydrophilic elements determines a virus’s ability to interact with the skin because it enables it to be transferred from other surfaces.
The hydrophilic protein part forms hydrogen bonds with the corneocytes of the epidermal barrier, while the lipid layer interacts with the lipid part of the skin through hydrophobic bonds.
Does water on its own get rid of the virus?
No: water is not enough because it only alters some of the interactions between the virus and our skin (hydrogen bonds).
As we all know from washing our hands, water is not able to remove lipid compounds on its own. We need a product that is either lipid-based (according to the chemical principle that “like dissolves like”) or surfactant-based (i.e. a foaming cleanser).
When a molecule with surfactant properties, namely with a hydrophilic head and a lipophilic tail, comes into contact with the virus, it can alter the lipid bilayer and remove the hydrophobic interactions which allow the virus to stick to the surface of the skin.
But it does a lot more than just that: by breaking through the external envelope, it causes the virus to fall apart.
So the “active” protein part is no longer able to keep the virus “alive” and whole, preventing it from spreading from one host to another and infecting them!
How do a hand sanitizers/alcohol-based products work?
Regular alcohol-based handrubs are liquid or gel hydro-alcoholic solutions; they have a concentration of 60 – 80% ethyl alcohol and contain antibacterial substances including sodium hypochlorite, which is now well known.
This compound is a salt which is widely used to disinfect water and sanitise environments. When alcohol is used in high concentrations, it has a denaturing3 effect, which means it alters the way the proteins of the bacteria and viruses bond, rendering them inactive. We just need small concentrations of sodium hypochlorite to oxidise4 or chemically modify all biological molecules, including the proteins and nucleic acids of viruses.
Disinfection using alcohol-based products with or without sodium hypochlorite is therefore highly effective in eliminating viruses.
Cleanser or disinfectant?
As we have seen, from a physico-chemical viewpoint, viruses are like small oily nanoparticles that can remain active on surfaces for hours to then be transferred onto our hands if we touch them. From our hands, viruses easily transfer to the mucous membranes when we touch our face, something we often do unconsciously.
Washing our hands with a surfactant-based product destabilizes the structure of the virus and has a similar effect to that of a disinfectant.
The use of alcohol-based hand sanitizers is only useful if we are unable to wash our hands.
So, the best advice for anyone suffering from dry or sensitive skin is to use a well-formulated cleanser with no aggressive surfactants whenever they can.
In cases like this, continuous use of sodium hypochlorite or other disinfectants can aggravate dry skin or cause irritation.
Washing our hands frequently has become a necessary precaution if we are to protect ourselves against COVID-19 infections but it is just as important to look after our skin, regularly applying emollients to repair the skin barrier.