How effective is hand sanitiser at killing germs?

Summer research students Kate Whyte and Rachel Chin set out to find just how effective soap and hand sanitiser is against microbes, such as bacteria and viruses.

Summer research scholarship students Kate Whyte and Rachel Chin

Does washing your hands or using hand sanitiser protect you from getting sick?

University of Adelaide scientist Hannah Agnew and summer research students Kate Whyte and Rachel Chin set out to find just how effective soap and hand sanitiser is against microbes, such as bacteria and viruses.

Since the emergence of COVID-19, hygiene practices have been more important than ever.

Using hand sanitiser soon became commonplace whenever you were out in public. Before we knew it, people were buying out all the soaps and hand sanitisers in stores, leaving empty shelves and creating opportunities for businesses to start manufacturing their own sanitiser.

Such a high demand for hand sanitiser came about as people opted to use sanitiser more than soap because of its easy transportation and no need for water.

We investigated how efficient soap and hand sanitiser are at killing bacteria. Bacteria and viruses are both tiny microbes that spread in similar ways and can cause disease.

Both microbes tend to have similar structures surrounding their internal components, which is targeted by soap and sanitiser.

Once these envelopes and membranes have been exposed to enough soap or sanitiser, the bacterium or virus will rupture and die. 

As we are based in a bacteria lab at the University of Adelaide, our focus on bacteria would still give us a good indication of the effectiveness of these hygiene practises against viruses like COVID-19.

The experiment

We performed a simple experiment where we pressed our unwashed hands against an agar plate and then placed it into an incubator to see how much bacteria would grow.

We then washed our hands with soap or used hand sanitiser and touched a different agar plate to incubate as well.

As a third test, we used both soap and hand sanitiser together to see if that would be even more effective than just using one by itself.

We left the agar plates for 24 hours and came back the next day to see how much bacteria had grown.

The results: Hand sanitiser

We found that using hand sanitiser works well at eliminating bacteria commonly found on our hands. Before using hand sanitiser, you can see that there was a large amount of bacteria present (Figure 1).

After using hand sanitiser there were very few to no colonies of bacteria left, as you can see on the plate. This indicates that hand sanitiser is likely very effective against COVID-19 and using it in public places where you are likely to be exposed to viral or bacterial particles will help protect yourself from infection.

Figure 1: Hand sanitiser effectively kills bacteria. The left two images show the agar plates with bacteria growing from unwashed hands. The right images show the bacteria that could grow after using hand sanitiser. That's a big difference!

The results: Soap

Unfortunately, with the soap treatment it appeared as if the soap hadn't really worked against the bacteria. This was unusual as the soap we used claimed it was an antibacterial soap (Figure 2). 

As it was an antibacterial soap we used, there could have been some bacterial contamination, possibly from the paper towel we used to dry our hands. Another explanation could be that the soap doesn't protect against all bacteria and is only effective against a small amount.

As we're not sure whether the bacteria grew due to contamination of the paper towel or whether the soap is selective against only some types of bacteria, it’s difficult to determine the effectiveness of the soap against COVID-19. 

Figure 2: Soap doesn’t appear to make much of a difference to the bacteria. Left shows the bacteria grown from an unwashed hand, with the right showing bacteria from a hand washed with soap. Clearly something weird was happening here, likely contamination from the lab equipment!

The results: Hand sanitiser and soap

We also examined plates of bacteria where we used both soap and hand sanitiser in combination.
For one of us, the soap and sanitiser combination was able to kill all the bacteria present on their hands (Figure 3).

With the other two people, it appeared that the contamination, which was affecting the results from the soap, was still present here. It resulted in lots of bacterial growth on the plates.

Figure 3: A soap and sanitiser combination was effective at killing the bacteria on one person’s hands (left images), but the other plates showed the same contamination that was present for the soap results (right images). 

Despite these mixed results, we recommend it is good practise to continue using both soap and hand sanitiser in combination whenever you are in a public area. This will decrease your risk of infection.

Although we were unable to show the effectiveness of soap against microbes, we can confidently say that hand sanitiser is effective at killing both bacteria and viruses.

Although we only looked at bacterial growth and no viral growth, these results are a good representation of what would happen to the viral particles on our hands when we use soap and sanitisers.

Overall, we have shown that hand sanitisers are extremely effective against bacteria and are expected to be as effective against viruses. We have highlighted the importance of hand hygiene practices in eliminating bacteria and viruses, protecting us against the spread of infections, including COVID-19.


About the authors 

Kate Whyte and Rachel Chin (pictured top of page) are both in the final year of a Bachelor of Science (Biomedical Science) and a Bachelor of Science (Advanced), respectively. Both are majoring in microbiology and immunology, and biochemistry.

Hannah Agnew

Hannah Agnew (pictured here) is currently researching one of the world’s deadliest pathogens, the bacteria Streptococcus pneumoniae.

Streptococcus pneumoniae causes around 190 million infections and 1 million deaths around the world each year. The bacteria are capable of causing different types of disease, from ear infections and pneumonia to infections in the brain. Although there are vaccines and antibiotics to protect against Streptococcus pneumoniae, they are not entirely effective. 

Hannah’s research is focused on discovering why a particular strain might cause one type of disease over another, e.g. a brain infection over a blood infection, by looking at differences between strains of the bacteria. By identifying key differences, she hopes to find new targets for therapeutics to prevent and treat diseases caused by Streptococcus pneumoniae.

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Tagged in Research, School of Biological Sciences, Biomedical Science, Biological Science, Research Centre for Infectious Diseases