Should we be worried about the 0.1% germs cleaning products don’t kill?

Clean it up by Judy, on FlickrSitting in front of the TV, it’s amazing how many times you hear the claim that a cleaning spray or a hand wash kills 99.9% of germs. Microorganisms are incredibly important to the environment and ourselves; our bodies are covered in them, so much so that they outnumber our own cells 10 to 1 – which is a good thing, as a lot of them help keep us fit and healthy. However some are harmful to us, and these harmful types include some bacteria, fungi and viruses – commonly known as germs.

The 99.9% claim (or 99.99%) that manufacturers put on their labels is certainly true for the tests that they carry out to check their products. However these tests are carried out under strict laboratory conditions and as usual real life is a little bit more complicated. The test they use is fairly simple; a known number of germs are placed into a certain amount of the cleaning product and left for a certain period of time. After the time has passed a sample is taken and tested to see how many bacteria have survived. Because a sample was taken in the industrial test (and the entire solution wasn’t subjected to the test) we cannot say we have killed 100% of the germs. Even if the entire solution was tested, the measurement of the number of bacteria will always differ from the actual result due to small inaccuracies in the experiment.

In real life we can’t dip our kitchens (or anything else we clean) into large vats of cleaning product and leave them there for a long time – it’s simply impractical – so we should expect to kill less than 99.9%. We may also miss areas when cleaning – like the hard to reach areas at the back of the microwave. Additionally, we may not read the instructions or use the correct amount of cleaning product.

However, even if we do not get rid of all of the germs when we clean we have greatly reduced their numbers whilst making our surfaces and hands a lot cleaner. The take-home message from this is you can never assume that cleaning will remove all the germs. There are, however, a lot of things you can do to reduce the spread of them in your home (click here to read some of them).

All of this hygienic talk is a start to make me want to go back and clean my microwave properly. Then again, microwave ovens kill bacteria and viruses, so I don’t have to bother, right? (Don’t count on it – Ed.)

Answer by Nathan Beal

Image Source: Clean it up by Judy, on Flickr

Article by Nathan Beal

November 6, 2014

Nathan is currently in the throes of a PhD in Computational Chemistry at the University of Manchester. When he’s not behind a computer, he’s outside enjoying the sights of the city. A fan of The Walking Dead, he has a strange apathy to all things football-related.


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