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Comment by ErrantX | Hacker News Reader

I've always wondered whether the growing modern obsession with bug killing and so forth might be counter productive.

Has anyone seen any studies they can recommend into the long term effect on our immune system?

What I'm more worried about is the claim that they kill 99.9% of germs. This would mean that the most resistant 0.1% get all the free space to grow. We're not disinfecting our world, we're creating evolutionary pressure on the germs to become resistant to our countermeasures.

Some things are easier to evolve a resistance to than others. The antibacterial measures we apply externally (rather than internally) tend to be more of the "would kill anything living" variety than the "targets specific, removable weakness of this organism". Hence, hard to adapt to.

Hand sanitizers, for example, work by immersing bacteria in alcohol, a potent organic solvent. It dissolves cell membranes and denatures proteins.

While there are bugs that can live in some pretty harsh conditions, to my mind, worrying about the bacteria in your kitchen sink spontaneously developing resistance to alcohol is like worrying about them spontaneously developing resistance to boiling water.

Possible, on the millions-of-years scale. Not exactly a big concern in this lifetime.

Another big reason resistance to alcohol (and boiling water) doesn't develop is that neither is persistent in the environment, and thus the selective pressure vanishes fairly quickly. The mutations required to resist either likely have downsides in normal environments, and thus will normally be selected against.

Does that mean they kill 99.9% of known germ types (i.e. some are resistant). Or that it is able to kill 99.9% of germs on a known object (i.e. some random subset of germs will escape destruction for whatever reason).

I suppose the former but I've never researched.

That's interesting. I always interpret it to be 99.9% of the population on a given surface. It could be read as types also I guess.

EDIT: the article posted here http://news.ycombinator.com/item?id=1031922 seems to support the 'types' theory, although it also casts significant doubt on the validity of the claims.

...and the other 0.1% kill you...

"we're creating evolutionary pressure on the germs to become resistant to our countermeasures"

I thought that's what we were doing anyway.

It's an arms race.

I share the same wonderment! In the 20 years of growing up in Kenya, I had never heard of anyone with allergies. I am baffled about how widespread allergies are in the US. Could the prolonged use of germ-killing products in the US cause this disparity? Unfortunately, I do not have statistics on allergy prevalence in Kenya vs. USA, and my wonderment is based simply on observation/experience.

[Edit]. The Hygiene Hypothesis (http://en.wikipedia.org/wiki/Hygiene_hypothesis): "In medicine, the hygiene hypothesis is a hypothesis that states that a lack of early childhood exposure to infectious agents, symbiotic microorganisms (e.g., gut flora or probiotics), and parasites increases susceptibility to allergic diseases by modulating immune system development"

[Edit2]. Statistics on the prevalence of allergies in the US: http://aaaai.org/media/statistics/allergy-statistics.asp

Alternate theory: there are different kinds of plants in the US versus Kenya. Humans happen to be allergic to the pollens that the US plants produce, and not allergic to the ones that the Kenyan plants produce.

One thing that definitely causes a lot of disease in the US is moldy buildings. Bringing in fresh air is expensive, so they just recirculate the dirty, moldy air. Then everyone gets sick, because mold in your lungs is not so good for you. (Actually, the mold gets stuck in your sinuses and then forms a film that is difficult to kill with antifungal medications. Fun! At least the building is "green"...)

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