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The Science Behind Hand Sanitiser

Source: Healthline

Group 5 Authors: Abby Cui, Elena Mao, Annabel Sutherland, and Ena Zheng

With the increased usage of hand sanitizer in classrooms as a direct result of the COVID-19 pandemic – a group of four students, (as part of their Group 4 Project for the International Baccalaureate Programme), has decided to investigate how hand sanitizer works, how it is made, and its effectiveness against viruses.

We present to you: Group 5’s Group 4 Project – The Science Behind: Hand Sanitizers

How Hand Sanitizer is Made:

Isopropanol vs Ethanol

Only two alcohols are permitted as active ingredients in alcohol-based hand sanitizers used against the  COVID-19 virus: ethanol or isopropyl alcohol. Alcohol solutions with the concentration range of 60-80% give optimum antimicrobial activity. Isopropyl and ethanol both have in-vitro activity against bacteria, fungi and some viruses. However, when tested at the same concentration, isopropyl is more effective than ethanol, with some exceptions of viruses where ethanol has greater activity than isopropanol.

Research on ethanol and isopropyl inactivation of COVID-19 bacteria on hard surfaces shows that concentrations of ethanol and isopropyl between 62-80% are very efficient at inactivating high numbers of COVID-19 bacteria within a 15 second contact time. Interestingly, at the highest concentration tested, (95% for both alcohols) a significant reduction on activation was observed.

Method of Production


  • 30 L bottle
  • 500 mL measuring cylinder
  • Distilled water
  • Smaller containers to store the finished hand sanitiser

Recommended quantities

Formulation 1 (ethanol)

  • 8333 mL Ethanol 96%
  • 417 mL Hydrogen peroxide 3%
  • 145 mL Glycerol 98%

Formulation 2 (isopropyl)

  • 7515 mL Isopropyl alcohol 99.8%
  • 417 mL Hydrogen peroxide 3%
  • 145 mL Glycerol 98


1. Pour alcohol into a large bottle. Hydrogen peroxide is then added using a measuring cylinder.

2. Add Glycerol using the measuring cylinder, making sure to rinse the cylinder with distilled water to extract any remnant glycerol.

3. Add 10 L of distilled water to the large bottle and mix the solution by shaking the bottle gently or using a paddle.

4. Immediately divide the solution into smaller containers and place the bottles in quarantine for 72 hours before use. This process allows time for any spores present to be destroyed.

Should we actually use home-made hand sanitizer?

Due to the evaporation of alcohol, its concentration in the final product must be measured using an alcoholmeter to ensure it is effective at killing germs and safe for usage.

On March 20th 2020, the U.S Food and Drug Administration (FDA) released its temporary guidelines for pharmacists and other manufacturers on making hand sanitizer. Under its recommendations, one must use pharmacy-grade ingredients, test alcohol levels in the final product, as well as label the finished formula. The FDA recommends the formula from the World Health Organisation (WHO), reiterating that adding additional active or inactive ingredients (such as aloe vera gel or essential oils) “may impact the quality and potency of the product”.

Source: Good House Keeping

The Composition of Hand Sanitizer:

The World Health Organization (WHO) recommends that household or local production factory produced hand sanitizers contain the following final concentrations of ingredients: ethanol 80%, glycerol 1.45%, hydrogen peroxide (H2O2) 0.125%, isopropyl alcohol 75%.

Ethanol is used due to its solubility in water and other organic compounds. The U.S. Centre for Disease Control and Prevention (CDC) recommends the use of hand sanitizer when water and soap is unavailable to kill microorganisms like bacteria, fungi and viruses. Hence, ethanol is a common ingredient in many hand sanitizers.

Alarmingly, The Food and Drug Administration (FDA) has announced recalls of hand sanitizers due to the presence of methanol. Methanol is a toxic alcohol that causes harmful side effects when applied on skin, such as nausea, vomiting, or headaches. When ingested, methanol may cause serious side effects such as blindness, seizures or damage to the nervous system. 

The Role of Hydrogen Peroxide in Hand Sanitiser

  • Low concentrations are used in hand sanitiser formulation to eliminate spores in bulk solutions. However, it is not appropriate for hand antisepsis.
    • Concentrations of 3-6% are used due to hydrogen peroxide’s tendency to cause corrosion and resourcing issues arising from the need to import from abroad

Glycerol in Hand Sanitiser

  • Acts as a humectant to keep things moist and increase rate of absorption
    • It is often used for skin care as it is readily affordable and available.
    • Adjusting the percentage of glycerol present changes the stickiness of the sanitiser

Other components

  • It is recommended that no other ingredients be added to hand sanitizer.
    • However, some hand sanitizers contain additional substances like methylethylketone and denatonium benzoate to reduce the rate of ingestion by making them purposefully less appetizing.
    • These additives causing a bitter taste may be transferred from sanitised hand to food. Hence, usage of other additives should be considered for their compatibility and acceptability.
    • Colorant may be used to differentiate hand sanitizer from other colourless fluids. It is suggested that as long as the additive is safe and compatible with essential components, it is appropriate to use.
    • The use of fragrances is not recommended due to allergen risk.
    • To reduce the risk of abuse and respect cultural sensitivities, all products can be labelled with “antimicrobial hand sanitizer”.

Hand Sanitizer or Soap?

Through comparing 3 different ethanol-based hand sanitizers and 3 different antimicrobial soaps, results found that all reduce  (>99.99%) of the tested enveloped viruses (including coronavirus). This means that in terms of their ability to inactivate viruses, ethanol-based sanitizers yield the same result as washing hands with soaps.

From a skin damage perspective, both alcohol-based hand sanitizers and soap detergents can cause irritation, itchiness, dryness and even dermatitis when used frequently. As lipids are important in keeping our skin’s stratum corneum’s water-binding capacity, it is important that lipids present in the solutions are not overly dissolved.

Thus, alcohol-based sanitizers are safer than alcohols. Since the lipid-dissolving effect of the alcohols is inversely related to their concentration, it can be concluded that hand sanitizers with higher alcohol concentrations are less damaging to the skin.

On the other hand, frequent handwashing leads to a progressive depletion of lipids, intensifying dryness and damaging the skin. Hence, high alcohol concentration hand sanitizers have the same efficacy of inactivating viruses as soap handwash, but is ultimately safer for our skin.

Source: Labroots

How Hand Sanitizer Kills Viruses:

With the ongoing coronavirus pandemic – which has seen over 58 million confirmed cases and over 1 million deaths – knowing how to protect ourselves and prevent infection has been at the forefront of world efforts to slow the spread of the disease. In the case of COVID-19, we are concerned with a virus that infects “host cells”, or in our case, human lung cells. With this infection, host cells are unable to continue their original function in the organism, ultimately leading to cellular death and the inability to carry out processes vital to the survival of the organism. Before we delve into this process, it may be helpful to fully understand the anatomy of a virus as well as defining some basic terminology.

To begin with, viruses are not considered living. This is because unlike humans and other living organisms, viruses are unable to survive and reproduce without the presence of a host. Most viruses are usually inactivated after a few hours outside a host. COVID-19 is a particularly robust virus, where some studies suggest they can remain active for several days in controlled laboratory conditions.

Source: Group 5 – Anatomy of a Virus

Some viruses have an envelope which acts in a similar manner to the cell membrane. They are made out of a phospho-lipid bilayer containing hydrophilic (hydro-water, philic-loving) heads and hydrophobic (hydro-water phobic-fearing) tails. This layer has the function of maintaining a barrier between the inside material of the virus and the outside environment.

Viruses also possess genetic material of either DNA or RNA in a “capsid”, which contains various sites that allow the virus to attach to a host cell and replicate this genetic material in order reproduce and survive. All these structures are required for the virus life cycle.

Source: Group 5 – Viral Envelope

Drawing back to hand sanitizers, they act predominately on the viral envelope and alter the structure itself – creating small micelles which ultimately render the original viral envelope ineffective at carrying out their function, resulting in an inactivated virus. However, because hand sanitizers target the viral envelope, the majority of hand sanitizers are therefore, ineffective at disabling non-enveloped viruses as they do not contain a lipid layer that the alcohol can act on.

We hope that this article has been able to inform you about the science behind hand sanitizer!


Davidson, M. Florida State University. ((2015, November 13). Virus Structure. Molecular Expressions. https://micro.magnet.fsu.edu/cells/virus.html#:~:text=The%20capsid%20has%20three%20functions,to%20inject%20the%20infectious%20nucleic)

Golin, A.P., Choi, D., & Ghahary, A. (2020). Hand sanitizers: A review of ingredients, mechanisms of action, modes of delivery, and efficacy against coronaviruses. NCBI. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7301780/

Government of South Australia. (2019). Alcohol-Based Hand Rub [PDF]. Government of South Australia, https://www.sahealth.sa.gov.au/wps/wcm/connect/e10fc9804fb5b324b085ba5cbc1ea1e9/FactSheet-Alcohol-based-hand-rubs_V4.1-phcs-ics-20190530.pdf?MOD=AJPERES&CACHEID=ROOTWORKSPACE-e10fc9804fb5b324b085ba5cbc1ea1e9-niQbKII

Riddell, S., Goldie, S., Hill, A., & Drew, T.W. (2020). The effect of temperature on persistence of SARS-CoV-2 on common surfaces. Virology Journal. https://virologyj.biomedcentral.com/articles/10.1186/s12985-020-01418-7

WHO. (2006). WHO guidelines on hand hygiene in Health Care [PDF]. WHO, https://www.who.int/patientsafety/information_centre/Last_April_versionHH_Guidelines%5B3%5D.pdf

Wikipedia. (2020). Corona Virushttps://en.wikipedia.org/wiki/Coronavirus



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