As the coronavirus pandemic hit, we were told to wash our hands for at least 20 seconds with soap or detergent several times a day. However, many people also called for alcohol gels to be made available in many workplaces, including schools. So, what is the difference between all these different methods of cleaning our hands? And does it really make any difference which we choose?!
What is soap?
Soap is made through a chemical process called saponification, where fatty acids in lipids get turned into salts. Soap can be made from animal fat or from vegetable fat and has the general formula (RCO2−)nMn+, where R is a hydrocarbon chain and M is a metal ion. A common example of a soap would be sodium stearate (C17H33COONa), made from steric acid which can be found in cocoa butter.
It is the structure of the soap molecule that allows it to lift and remove grease. The head of the molecule contains the metal ion and this allows the molecule to dissolve into polar solvents like water. The tail is a hydrocarbon chain that can only dissolve in non-polar substances. So, the soap molecule acts as a surfactant and lowers the surface tension between the two phases which causes droplets of lipids to mix with the water.
The specific virus that causes COVID-19 is called SARS-CoV-2 and is a type of coronavirus. This group of viruses have been so named due to having a crown-shaped outline caused by their surface proteins.
When SARS-CoV-2 is viewed through a high power microscope, it is possible to observe a fatty envelope that holds the virus together and keeps it active. Having soap in contact with the virus particles for at least 20 seconds can cause the breakdown of this membrane and this renders the virus inactive.
What is detergent?
Synthetic detergents were first made in the early 1900s by German scientists because the first world war had blocked their importing of raw materials to make soap. Detergents are like soap as they too are surfactants that contain a hydrophilic head and hydrophobic tail. However, they have a different general formula of R-SO4– Na+, and the sulfonate group means that detergents do not readily react with calcium ions, preventing the generation of scum in hard water areas. Many synthetic detergents contain non-ionic surfactants like sodium laureth sulfate which belong to the akylbenzenefulfonates family of chemicals. Detergents are formulations, as the synthetic detergent itself is not as effective as soap in cleaning.
SARS-CoV-2 virus is an enveloped virus, and it has been shown to be quite fragile. So, as long as the lipid layer of the virus has been removed, it is unable to invade human cells and cause the Covid-19 disease. Currently, many experts believe that hand washing in detergent will cause the lipid layer to be damaged, as detergents have been shown to deactivate enveloped viruses such as adenovirus [1]. However, the Government recommend that, when cleaning hard surfaces, a household detergent followed by disinfection is recommended and the disinfectant should be checked to ensure that it is effective against enveloped viruses.
What is hand sanitiser?
If you cannot wash your hands with water and a cleaning agent, then alcohol gel is better than nothing. However, hand sanitiser has the active ingredients ethanol and propan-2-ol, which must be at least 60% of the product. Non-alcohol hand sanitisers contain antimicrobial agents but are even less effective than their alcohol-containing counterparts. When using a hand sanitiser, you must make sure that you cover all parts of the hands and rub hands together for 20-30 seconds until your hands feel dry.
This method of cleaning hands is significantly less effective at disease transmission and has been shown not to prevent Clostridium difficile (C.difficile, C. diff) and, more recently, norovirus (winter vomiting bug), as well as being completely ineffective against spores such as athlete’s foot. Research has shown that an alcohol concentration exceeding 90% is needed to kill most viruses and this is not seen in hand sanitisers you’ll find in the shops, only in medical settings as alcohol rubs.
What does this mean for us returning to school?
Washing of hands using soap is very important to remove the possibility of coronavirus, and other pathogens, spreading on different surfaces. So, plenty of soap should be available with water for frequent handwashing for at least 20 seconds. Students should be encouraged to wash their hands after they blow their nose, sneeze into a tissue, go to the toilet, when they leave and return to each room, as well as before preparing or eating food.
Desks, computers, phone and door handles should be cleaned frequently with disinfectant. Disinfectant products should be easily available at each workstation for people to clean before they use them.
How can we use the coronavirus pandemic as a learning tool?
Every person across the world has gained cultural capital as they have lived through this unprecedented time and been part of history as it unfolds. As teachers, we can build on the knowledge that they have and use it to underpin the learning that they need for their GCSE Science. Some ideas include:
- As part of the Infection and Response topic in AQA GCSE Biology and AQA Trilogy, students need to understand the structure of a virus and the coronavirus could be used as a worked example. Extend students by explaining that many scientists do not consider viruses to be alive, as they do not complete the seven life processes unless they are in a living cell.
- You can hold a class role play for students to debate the use of antibiotics to treat coronavirus – this addresses a common misconception as many students do not understand that antibiotics are only affective against bacterial infections and not viral infections.
- Students can also consider disease transmission and learn how to prevent this by washing hands.
- You may wish to make soap and detergent with your classes. See this Royal Society of Chemistry practical.
- Give students this selection of graphs and charts produced about the pandemic. Ask students to classify the type of methods used to display the data and state the independent and dependent variables. All students should describe the pattern in the data, most students should be able to explain the changes in the data and a few students should be able to evaluate the usefulness of the data.
So, as I finish typing this, I wish for everyone to stay safe and keep well. You must excuse me as I now need to sing happy birthday twice since an hour has lapsed and I need to breakdown the fatty protection of any coronavirus that may be on my hands! Oooh, and let’s just wipe down the keyboard, and my mobile phone and . . . . .
[1] https://www.sciencedirect.com/topics/nursing-and-health-professions/detergent
Sam Holyman is Second in Science at Aylesford School in Warwick, and formerly West Midlands ASE President. She is also the author of a number of best-selling science textbooks for KS3 and GCSE (including the AQA GCSE Foundation: Combined Science Trilogy and Entry Level Certificate Student Book), and a keen advocate of innovative teaching and learning.
Sam was nominated in the Teacher Scientist category for the Science Council’s 100 leading practising scientists, is a Chartered Science Teacher, and has recently been awarded a CPD Quality mark.
