Covid-19: Why Soap Works

[iluvtennis]

Why Soap Works

At the molecular level, soap breaks things apart. At the level of society, it helps hold everything together.

By Ferris Jabr, March 13, 2020

It probably began with an accident thousands of years ago. According to one legend, rain washed the fat and ash from frequent animal sacrifices into a nearby river, where they formed a lather with a remarkable ability to clean skin and clothes. Perhaps the inspiration had a vegetal origin in the frothy solutions produced by boiling or mashing certain plants. However it happened, the ancient discovery of soap altered human history. Although our ancestors could not have foreseen it, soap would ultimately become one of our most effective defenses against invisible pathogens.

People typically think of soap as gentle and soothing, but from the perspective of microorganisms, it is often extremely destructive. A drop of ordinary soap diluted in water is sufficient to rupture and kill many types of bacteria and viruses, including the new coronavirus that is currently circling the globe. The secret to soap’s impressive might is its hybrid structure.

Soap is made of pin-shaped molecules, each of which has a hydrophilic head — it readily bonds with water — and a hydrophobic tail, which shuns water and prefers to link up with oils and fats. These molecules, when suspended in water, alternately float about as solitary units, interact with other molecules in the solution and assemble themselves into little bubbles called micelles, with heads pointing outward and tails tucked inside.

Some bacteria and viruses have lipid membranes that resemble double-layered micelles with two bands of hydrophobic tails sandwiched between two rings of hydrophilic heads. These membranes are studded with important proteins that allow viruses to infect cells and perform vital tasks that keep bacteria alive. Pathogens wrapped in lipid membranes include coronaviruses, H.I.V., the viruses that cause hepatitis B and C, herpes, Ebola, Zika, dengue, and numerous bacteria that attack the intestines and respiratory tract.

When you wash your hands with soap and water, you surround any microorganisms on your skin with soap molecules. The hydrophobic tails of the free-floating soap molecules attempt to evade water; in the process, they wedge themselves into the lipid envelopes of certain microbes and viruses, prying them apart.

“They act like crowbars and destabilize the whole system,” said Prof. Pall Thordarson, acting head of chemistry at the University of New South Wales. Essential proteins spill from the ruptured membranes into the surrounding water, killing the bacteria and rendering the viruses useless.

In tandem, some soap molecules disrupt the chemical bonds that allow bacteria, viruses and grime to stick to surfaces, lifting them off the skin. Micelles can also form around particles of dirt and fragments of viruses and bacteria, suspending them in floating cages. When you rinse your hands, all the microorganisms that have been damaged, trapped and killed by soap molecules are washed away.

On the whole, hand sanitizers are not as reliable as soap. Sanitizers with at least 60 percent ethanol do act similarly, defeating bacteria and viruses by destabilizing their lipid membranes. But they cannot easily remove microorganisms from the skin. There are also viruses that do not depend on lipid membranes to infect cells, as well as bacteria that protect their delicate membranes with sturdy shields of protein and sugar. Examples include bacteria that can cause meningitis, pneumonia, diarrhea and skin infections, as well as the hepatitis A virus, poliovirus, rhinoviruses and adenoviruses (frequent causes of the common cold).

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Soapy water is the number one deterrent. Sanitizers and alcohol wipes are effective, but not as much as soap.

[TheBlackAdder]

1. Plus you're cleaning the entire hand, washing most of it away, instead of lingering virus cells.

[iluvtennis]

2. Exactly. nt

[GoCubsGo]

3. Which is why I have not worried about having hand sanitizer.

I always have plenty of soap on hand. The one good thing about this pandemic is that it's finally getting people to wash their damn hands. I can't believe they still have to be told to do this.

[FarPoint]

4. Nurses learn this in ...

First Quarter Nursing 101

[blogslut]

5. I fell in love with soap in cosmetology school.

It's magical.

[ProfessorGAC]

6. This Article Is Solid

Good description of the mechanism and fairly accurate, though simplified, with regard to the physical chemistry.
A couple of nits to pick:
Soap & detergents are not the same thing, chemically.
Soaps tend to work as described, but are further strengthened by the relatively high pH (~8) which bacteria, in particular, don't like.
Detergents have the mechanism described but are more efficient because of the higher ionic strength of the primary surfactant.
We call the squirt bottle "liquid soap" but there's no soap in 99% of commercial brands. The formulas with antimicrobial contents use more nonionic surfactant, so the efficacy on microbes of the surfactant is substantially weaker, but then we've got an actual microbe killer in the formula.
Second nit: the idea of "soap" cleaving things at the molecular level is overstated. The level of this activity is microscopic, or even nanoscopic, but the activity is much more macromolecular. The very drawing in the article shows the micellization to be caused by groups of molecules.
Those are details, though.
The upshot here is that surfactants (both soaps & detergents) are fairly good antimicrobial agents, and those you don't kill get flushed down the drain. Gone is just as good as dead in most cases.

[iluvtennis]

7. Thanks for the added clarifications. As I always say, you never who is on DU.