On Tue, Apr 28, 2009 at 05:08:57PM -0500, Nick Wright scripsit: > My problem with those little bottles of hand sanitizer is that it only > kills 99.9% of germs. > > The manufacturers tout this as a feature (they proclaim it right on > the bottles), but I see it as a liability. > > Because that 0.1% of germs that survive to reproduce will logically be > the strongest most horrible versions of the germ.
Nope. Generally, they'll be the germs that got the least amount of exposure to the alcohol. It says nothing about how virulent they are. Generally you *want* to make the selection about surviving nasty chemicals rather than being an efficient parasite of humans. The bug that learnt how to metabolize chlorine bleach is scary to think about, but it now *needs* chlorine bleach, and there is (I hope!) none inside you. > It's natural selection speeded up many times. We destroy the weakest > strains of the germ, and leave the strongest to continue spreading. A billion years of yeast hasn't found one that can cope with more than about 25% ethanol. I'm not worried we're going to produce something that can shrug alcohol (or put all the distillers out of work by making 90 proof wine) and what you're really doing by washing your hands is reducing the odds of systemic infection. > And meanwhile our bodies never develop any kind of natural immunity. Sure they do. It just doesn't get overwhelmed. All killing 99.9% of the germs on your hands does is multiply the default risk of systemic infection by 0.01 (because it's really going to be 99% unless you're emulating the lab conditions of the test; mind you got all of both thumbs...); if that risk is a chance of 0.1 out of 1 per exposure (one handshake, one nearby sneeze, etc.) it becomes 0.001. If you're exposed 10 times at the 0.1 chance that's (0.9)^10 = 0.35 that you *won't* get it. (Which is two chances in three that you _will_.) If you're exposed 10 times at the 0.001 chance that's (0.999)^10 = 0.99 that you *won't* get it. (One chance in a hundred that you _will_.) Since people constantly touch their faces and get what's on their hands into the mucous membranes (eyes, nose, mouth) that way, this is very much worth doing with respect to contagious diseases. Alcohol sanitizers are preferred for cases where there's no obvious soiling; it's easier on your skin and works just as well. Mind you get both thumbs. -- Graydon, who will admit to a bit of a bee in his bonnet about this. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
