• Question: How do hand sanitizers work, and how effective are they against bacteria.

    Asked by lani to Chris, Emily, Martin, Natalie, Tamsin on 18 Mar 2010 in Categories: .
    • Photo: Natalie Stanford

      Natalie Stanford answered on 18 Mar 2010:

      Hand sanitizers contain a high amount of of alcohol such as ethanol or propanol, which are very effective at killing most bacteria. As long as your hands aren’t visibly dirty ie covered in mud, they are safe alternative to washing them. If you have sensitive skin they may not be so good for you, however. I have to use a hand sanitizer after I’ve been working in the labs because I’m allergic to the soap we use in there.

    • Photo: Martin Coath

      Martin Coath answered on 18 Mar 2010:

      Another good question!

      There are LOADS of synthetic chemicals that will kill bacteria and hand sanitizers often contain more than one of them.

      They often have natural substances like tea-tree oil as well. This has been shown to be effective against some infections.

      They mix all this stuff with water, or alcohol, or aloe-vera gel, or witch-hazel, or synthetic thickener or more than one of these things – and thats it, done 🙂

      The names of all the chemicals they can use are pretty meaningless. The one I use has Triclosan in it which is a chlorinated phenoxy-phenol. You can google Triclosan – but better still you can take chemistry A level and find out what that means! It is fun!

    • Photo: Emily Cook

      Emily Cook answered on 18 Mar 2010:

      They contain alcohol which kills the bacteria, but other ingrediants make it poisonous so those who’ve thought it a good idea to drink it have wound up in hospital having their stomachs pumped.

      Manufacturers claim they kill 99.9% of bacteria. This is partly true and partly a lie.
      Tests are done on flat, smooth surfaces, like in a glass beaker or a petrie dish. In these conditions the gel will kill most of the bacteria, and experiments like this are where the number 99.9% comes from.

      However, our hands are actually cracked and creviced and generally not smooth, so the the percentage of bacteria actually killed on your hands would be far less. Experiments like this are harder to do and keep fair so there aren’t any numbers to say how much less.

      Not all scientists agree if they are useful. Some studies have shown that washing your hands with soap and water is still better, while others show that they can stop the spread of tummy bugs within a family. I suppose using them if you can’t get to a sink can’t hurt, but if you can, wash as normal!

    • Photo: Chris Cooper

      Chris Cooper answered on 18 Mar 2010:

      Basically the alcohol strips the surface of the skin of oil. This makes it harder for bacteria to settle. But there is no real evidence that they are better than soap and water. So in our lab we use alcohol (more concentrated than a hand sanitizer) to kill bacteria on our benches. But we have an old fashioned sink with liquid soap at the exit of the blood lab.

      I’ve just seen the other answers: this web site has some details about the debate of hand sanitisers vs soap and water:

      http://biology.about.com/od/microbiology/a/handsanitizers.htm

      and here’s a Daily Mail article which discusses the issue in the context of swine flu (normally the Mail way too scare-mongering about science stories, but this is not too bad actually).

      http://www.dailymail.co.uk/health/article-1201283/So-Swine-Flu-hand-gels-really-work.html

      Of course in a hospital it is difficult to have sinks everywhere so having an alcohol-based hand sanitizer at the entrance and exit of wards is better than nothing.

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