Updated: Oct 25
Experts have been telling us to wash our hands as often as possible since the beginning of the coronavirus epidemic, and faced with shortages of alcohol-based hand sanitizer, more and more people are turning to traditional natural soap from Marseille. In fact, soap is much more effective at killing the virus than alcohol-based disinfectants and the following article by professor Pall Thordarson explains why.
Viruses can be active outside the body for hours, even days. Disinfectants, liquids, wipes, gels, and creams containing alcohol are all useful at getting rid of them – but they are not quite as good as normal soap.
Your grandmother’s bar of soap kills the virus.
When I shared the information above using Twitter, it went viral. I think I have worked out why. Health authorities have been giving us two messages: once you have the virus there are no drugs that can kill it or help you get rid of it. But also, wash your hands to stop the virus spreading. This seems odd. You can’t, even for a million dollars, get a drug for the coronavirus – but your grandmother’s bar of soap kills the virus.
So why does soap work so well on the Sars-CoV-2, the coronavirus and indeed most viruses? The short story: because the virus is a self-assembled nanoparticle in which the weakest link is the lipid (fatty) bilayer. Soap dissolves the fat membrane and the virus falls apart like a house of cards and dies – or rather, we should say it becomes inactive as viruses aren’t really alive.
The slightly longer story is that most viruses consist of three key building blocks: ribonucleic acid (RNA), proteins and lipids. A virus-infected cell makes lots of these building blocks, which then spontaneously self-assemble to form the virus. Critically, there are no strong covalent bonds holding these units together, which means you do not necessarily need harsh chemicals to split those units apart. When an infected cell dies, all these new viruses escape and go on to infect other cells. Some end up also in the airways of lungs.
When you cough, or especially when you sneeze, tiny droplets from the airways can fly up to 10 metres. The larger ones are thought to be the main coronavirus carriers and they can go at least two metres.
These tiny droplets end on surfaces and often dry out quickly. But the viruses remain active. Human skin is an ideal surface for a virus. It is “organic” and the proteins and fatty acids in the dead cells on the surface interact with the virus.
When you touch, say, a steel surface with a virus particle on it, it will stick to your skin and hence get transferred on to your hands. If you then touch your face, especially your eyes, nostrils or mouth, you can get infected. And it turns out that most people touch their face once every two to five minutes.
Washing the virus off with water alone might work. But water is not good at competing with the strong, glue-like interactions between the skin and the virus. Water isn’t enough.
Soapy water is totally different. Soap contains fat-like substances known as amphiphiles, some of which are structurally very similar to the lipids in the virus membrane. The soap molecules “compete” with the lipids in the virus membrane. This is more or less how soap also removes normal dirt from the skin.
The soap not only loosens the “glue” between the virus and the skin but also the Velcro-like interactions that hold the proteins, lipids, and RNA in the virus together.
Alcohol-based products, which pretty much includes all “disinfectant” products, contain a high-percentage alcohol solution (typically 60-80% ethanol) and kill viruses in a similar fashion. But soap is better because you only need a fairly small amount of soapy water, which, with rubbing, covers your entire hand easily. Whereas you need to literally soak the virus in ethanol for a brief moment, and wipes or rubbing a gel on the hands does not guarantee that you soak every corner of the skin on your hands effectively enough.
By Pall Thordarson, professor of chemistry at the University of New South Wales, Sydney.
Driven by consumer tastes for wholesome products, Marseille soap is now said to be overtaking liquid soaps and shower gel, which are seen to contain too many chemicals and use too much single use plastic. This iconic little soap was a pioneer of the organic trend long before its time - its creation dates back to the 15th century in Marseille, when soap makers began to prefer using olive oil instead of animal fat, which explains the green shade we know and love today.
Marseille soap, or Savon de Marseille, is presented as a pale-green, brownish cube or bar bearing the stamp “72% extra-pure,” and has become a Provençal icon. In recent years, this rustic little block, traditionally used for washing linen, has made its way from the supermarket aisles into our kitchens and bathroom cabinets. In recent years, manufacturers have quarrelled over its origin and it has made its way into the news, but one thing remains the same - the recipe has remained unchanged for centuries.
Generations of French women have used Savon de Marseille to remove persistent stains from linen, or to bathe delicate skin. This particular soap is biodegradable, hypoallergenic, nourishing, imperishable, moth repelling, naturally anti-bacterial, and free from colourants and artificial fragrances. As a result, it was one of the French hygiene products that contributed to the drop in infant mortality rates and contagious diseases during the 19th century and in Provence, France, some say it has quite extraordinary properties.
So, soap is the best, but do please do continue to use alcohol-based sanitiser when soap is not handy or practical.