Emilio Romero Jouvin asked:
My daughter Camila raised a very interesting question while watching a commercial for a sanitizing or disinfecting gel that claimed to get rid of 99.9% of germs: other than being curious as how do they know with such accuracy the performance of the product, she asked what would happen if one uses the gel twice... will it get rid of 100% of the germs (sounds logical ha ha).
Thank you and best regards as always. Great show, keep up the good work.
Greetings from Ecuador
We put this question to Jane Greatorex from the Health Protection Agency in Cambridge:
Jane - Well, it’s not a straightforward answer. The 99.9% claim that manufacturers put on their products is true based upon the tests that they carry out, but these are carried out under laboratory conditions in test tubes and on plates. It’s a little bit more complicated than that in real life and it really depends on what we’re talking about here.
(c) Lars Klintwall Malmqvist @wikipedia" alt="Person washing his hands" />If we’re talking about a cough droplet, a cough droplet might contain about 200 million 'flu germs in the winter season and about a million or so bacteria; and if you use that hand gel, then you will indeed get the numbers of viruses and bacteria down probably to levels below that which is infectious.
However, you will not remove all of them and that's because of two things. One, your hands are very good at retaining bacteria and viruses, and two, the numbers of bacteria and viruses that you start with are such that even 0.1% is still a big number of bacteria and viruses. If you kill even that 0.1% with another hand wash, you'll still be left with some remaining.
Now if, for instance, we were talking about faecal contamination – not a nice subject, but then we’re talking about much larger numbers of viruses and bacteria, and the big complication there is, you need fewer of those to cause an infection.
So, the straight answer is, you won't remove all the bacteria and viruses, and that's in some situations, it’s really not very good news.
Diana - Two scrubbings will remove more germs, but 99.9% of a lot is still going to be a lot. It all depends on what the infectious doses of a specific pathogen. If you only need one bacterium to infect you and sometimes even the most thorough washing isn’t enough.
Its quite logical to think it that way. For example, when you brush your teeth once it is not as effective as you brush your teeth twice. As for sanitizers, I think it has something to do with how much of it you apply to lets say your hand.
Well, obviouisly, you'll kill 99.999% of the germs. And, if you wash your hands three times, you'll kill 99.99999% of the little blighters. Geezer, Tue, 25th Jan 2011
The question should be why you are not killing 0.1% of the "germs".
Come to think of it, we might ask how they know it kills 99.9% Did they actually count them?
When you clean everything with that product but then catch some nasty little germ, guess what.... Yep, it was the 0.1% that the product didn't kill. Its the manufacturer's 'get out' clause.
Oh, this is fun! ....
We recieved this from Ian Smith. I'm sure he'll be happy for me to post it here:
It's good to see kids thinking skeptically. First the claim of 99.9% germ killing is largely theoretical. Your biggest variable is the surface on which you want to clean. If the surface is PERFECTLY smooth even down to the microscopic scale (The scale of most "germs") and the antiseptic is PERFECTLY made and used (all three highly unlikely) then you'll kill 99.9% of the germs present. You'll be left with about 1 in 1000 germs left, still a lot of germs. If you clean again you'll not kill 99.9% of the germs left as these are the germs that happened to be in places where they are protected or are for other reasons immune. It's the second one, the immunity, that is a bit scary. Those bugs that survive will now breed and their dependents will also be immune, which means your antiseptic will be less effective. This is how evolution works. Take a group of organisms and introduce a stress, like a toxin, that kills most, but not all the individuals who experience the stress. Now wait a while for your population to rebuild and introduce the stress again. Again a lot of individuals will be killed but, all other things being equal, you'll have a lot more survivors than you did the first time. Repeat this cycle over and over and soon the stress will only kill a small number of individuals. mountaineirc1969, Thu, 27th Jan 2011
For proper hand washing technique.... you should follow the example of a surgeon. It should take you a few minutes to complete the process.
Well... Mutations occur with every generation of a certain organism, one of the generations for a specific bacteria could be immune to the chemicals in the sanitizer gel.
It's incredibly stupid to want to kill of the organisms we live with. Use soap, it will clear of the dirt to about 99%, but stop trying to kill the natural bacterias you have. We have evolved with those, and a effect of blind faith in 'hygiene' is that your kids will have a lower resistance to a lot of common diseases.