Why does soap work so well on Coronavirus Covid-19

Why does soap work so well on Coronavirus Covid-19

Why does soap work so well on the coronavirus and indeed most viruses? Because it’s a self-assembled nanoparticle in which the weakest link is the lipid (fatty) bilayer.

Soap dissolves the fat membrane and the virus “dies”, or it becomes inactive as viruses aren’t really alive. Viruses can be active outside the body for hours, perhaps days.

Disinfectants (and soap) have similar effects but are not really quite as good as regular soap. But why exactly is soap so good? To explain…

A bit about viruses
Most viruses consist of three key building blocks: RNA, proteins and lipids. The RNA is the viral genetic material – it is very similar to DNA. The proteins have several roles including breaking into the target cell, assist with virus replication and basically to be a key building block (like a brick in a house) in the whole virus structure.

The lipids then form a coat around the virus, both for protection and to assist with its spread and cellular invasion. The RNA, proteins and lipids self-assemble to form the virus. Critically, there are no strong bonds holding these units together.

Instead, the viral self-assembly is based on a weak interaction between the proteins, RNA and lipids. Together this actst like Velcro so it is very hard to break up the self-assembled viral particle. Still, we can do it (with soap!).

Most viruses, including the coronavirus, have complex interactions with surfaces they are on. Skin, steel, timber, fabric, paint and porcelain are very different surfaces. Similar molecules appear to interact more strongly with each other than dissimilar ones. Wood, fabric and not to mention skin interact fairly strongly with viruses.

Contrast this with steel, porcelain and at some plastics, e.g. Teflon. The surface structure matters – the flatter the surface the less the virus will “stick” to the surface. Rougher surfaces can actually pull the virus apart.

So why are surfaces different?
The virus is held together by a combination of hydrogen bonds (like those in water) and hydrophilic or “fat-like” interactions. The surface of fibres or wood, for instance, can form a lot of hydrogen bonds with the virus.

In contrast steel, porcelain or Teflon do not form a lot of hydrogen bond with the virus. So, the virus is not strongly bound to these surfaces. The virus is quite stable on these surfaces whereas it doesn’t stay active for as long on say fabric or wood.

For how long does the virus stay active?
It depends. The SARS-CoV-2 coronavirus is thought to stay active on favourable surfaces for hours, possibly a day. Moisture, sunlight (UV) and heat all make the virus less stable.

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 through both hydrogen bonds and the “fat-like” hydrophilic interactions. When you touch say a steel surface with a virus particle on it, it will stick to your skin and hence get transferred onto your hands. But you are not (yet) infected. If you touch your face though, the virus can get transferred from your hands and on to your face.

And now the virus is dangerously close to the airways and the mucus type membranes in and around your mouth and eyes - the virus can get in…and you are infected (that is unless your immune system kills the virus).

Soap contains fat-like substances knowns as amphiphiles, some structurally very similar to the lipids in a virus membrane. The soap molecules “compete” with the lipids in the virus membrane. This is more or less how soap also removes normal dirt of the skin. The soap is effectively dissolving the glue that holds the virus together. The soap also outcompetes the interactions between the virus and the skin surface. Soon the viruses get detached and fall apart. The virus is gone!

The article above is a precis of an article written by Professor Palli Thordarson of the University of New South Wales and obtained via open source.