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Why Sanitizers Don’t Clean

 Back when I was a medicinal chemistry intern, we had high school students run experiments during the summer and make posters presenting their results. It encouraged them to become interested in science and all that good stuff…

One of the posters was about a study run to determine the most optimal way to clean ones hands. The “cleanest” hands would have the least amount of live bacteria present.

The experiment involved inoculating (exposing to bacteria in a controlled fashion) 3 different sample groups with bacteria (n=3) then coating them with one of the 3 sanitizing reagents.

Hand Sanitizer: Total Kill: 50%

Washing with Soap and Warm Water: Total Kill: 98%

70% Isopropanol (over the counter rubbing alcohol): Total Kill: 75%

The hand sanitizer only killed 50% of bacteria present on the sample which would leave your hands covered in 50% dead bacteria and 50% live (still multiplying) bacteria. This was contradictory to the 99% kill claim that many companies make. I thought about it for a while but eventually let it go because it was a high school project.

Last week I sat in on a Montana State Biofilm Webinar which explained that the intracellular matrix that bacteria form when bound to a surface is almost impossible to kill. The explanation is complex but in simple terms, the top layer of bacteria exposed to sanitizing agents acts as a “sacrificial layer” thus preventing lower layers from exposure to reagents.

So basically, if you want clean hands, you must remove the bacteria by washing them with soap and water…

 Kind of gross thinking about how many times I’ve used hand sanitizer instead of washing my hands before eating haha.