The dirty lyes about soap – News

Isopropyl wipes vs standard liquid hand soap

An investigation by Tim while on work experience at GTAC

When working in a lab I had to wash my hands quite frequently, and it became something regular to do when I entered the lab and when I left. Being around some of the best equipment and scientists in the world (at least to me), made me wonder about the effectiveness of the liquid hand soap we were using in comparison with something more accepted, such as hospital grade isopropyl wipes. Bacteria wise, is there a point to washing my hands before and after entering the lab? Should we be using hospital grade cleaning products for our skin? When I leave the lab am I leaving with hands full of bacteria? And does using paper towel after I wash my hands impact this? These questions I knew I had to answer.

I thought to myself that there would be less bacteria found on my hands after using the isopropyl wipes due to the “hospital grade” of the wipes, compared with using the SLS liquid hand soap found in the GTAC lab. I also figured that there would be less bacteria found on my hand after washing and not using the paper towel compared with using the paper towel, as it seemed to make sense that the less I touched the less bacteria I would be able to pick up on my hands.

I designed an experiment to use LB Agar plates to check for growth of bacteria following cleaning my hands with liquid hand soap, isopropyl wipes and using and not using paper towel after washing my hands. LB Agar plates are round dishes that contain LB and agar. The LB is the nutrient mix for bacteria to grow and the agar makes it solid so the bacteria make colonies when they grow. We use this so that it is clearly visible which bacteria survived my hand cleaning. First of all we would need a negative control group, which would be an agar plate, coated with deionised water. If bacteria grew on this plate we would know that the equipment used would be contaminated and our results may be incorrect. My second plate would be my second control, where I would test how much bacteria I had on my hands before any type of cleaning. For this I placed my left thumb, my right thumb and my left index finger on the LB Agar plate. My third plate was where I would wash my left thumb with liquid hand soap and not towel dry, then place my wet thumb on the plate. My fourth plate was used for my right thumb, which I washed with liquid hand soap but towel dried. My fifth and final plate was used for my left index finger, which I cleaned thoroughly with the isopropyl wipes. To allow the bacteria to grow I incubated the plates at 37, a temperature which most bacteria are able to grow at. I checked the LB Agar plates 48 hours after pressing my fingers against them and took pictures. My results are as shown in the table.


Bacteria had grown and it was clearly visible. Comparing plate 4 and 5 with plate 2 provided me with my conclusion about which is more effective, standard liquid hand soap or hospital grade isopropyl wipes. Interestingly, after I wiped my right thumb with isopropyl wipes I had 5 more (20) colonies of bacteria than I had to begin with (15), whereas liquid hand soap reduced by 5 (17) the amount of colonies of bacteria I had before I washed my left thumb (22). It was quite clear that there was a point to making sure you dry your hands after washing as when I left thumb wet after washing, the amount of bacteria I had before and after washing my hands actually increased by a whopping 8814%. When you compare this figure with the amount of bacteria I had on my hands after towel drying (decreased by 23%), it is quite clear that not drying your hands defeats the purpose of washing with liquid hand soap. Interestingly, the opposite of what I thought would happen occurred. The liquid hand soap appears to be more effective at removing bacteria than the hospital grade isopropyl wipes and drying your hands with paper towel after washing actually removes more bacteria than leaving them wet.

However I cannot be certain about the implications of my results, as it was only conducted once and had a few possibilities for error. Before I ran my experiment I did not gather all my materials and equipment which resulted in a great lapse of time in between cleaning my thumb with the isopropyl wipes and pressing it against the LB Agar plates. This meant that there was a greater possibility that I may have touched something in-between wiping and pressing my thumbs against the plates, as I had to navigate a multi floor office environment with people who have been sick. This could interfere with the comparison between liquid hand soap and isopropyl wipes as the conditions in which the experiment was conducted was not kept consistent between the two. If I were to further investigate this matter I would investigate whether the bacteria content of Melbourne tap water would have impacted the amount of bacteria on my hands after washing with soap. This could be tested in the same way as I tested the equipment in the first plate, I could take a swab, wet it with tap water and coat the LB Agar plate with it, then test for bacteria growth after 48 hours. In the future I would also have gathered all my materials prior and had used more people to ensure that I was obtaining concordant results. This would also indicate how much difference in bacteria amount is significant.

So all in all my hypothesis was not supported, the results were actually completely opposite. I however did answer all my questions. Yes there is a point to washing my hands with liquid hand soap after leaving the lab. My results showed that we don’t need to use hospital grade products on our skin, as the isopropyl wipes actually resulted in more bacteria than what I began with. Yes my hands still do have bacteria on them after leaving the lab, but not in amounts that I need to worry about. And finally I do need to worry about drying my hands after washing them, if I don’t I’m actually walking away with 8814% more bacteria than what I started with on my hands.

To finish up, this experiment was just a small part of a massive week that I’ve enjoyed here at GTAC, I have to say how thankful I am to the brilliant scientists/teachers who work here. I keep thinking to myself how privileged I am, I could have ended up doing work experience slaving away at a local supermarket, or shuffling papers at some bureaucracy, but I ended up at GTAC, doing something that I love: science.