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> The researchers used different strengths of alcohol concentrations to combat the bacteria, starting with 23 percent. Eventually, at a 70-percent alcohol mixtu

> The researchers used different strengths of alcohol concentrations to combat the bacteria, starting with 23 percent. Eventually, at a 70-percent alcohol mixture, the bacteria were conquered. Typically, hand sanitizers are 60 percent alcohol. Is it simply a matter of using higher concentrations of alcohol? Or is it possible that bacteria could evolve resistance right up to 100%?

hcurtiss 8y ago
It’s not like an antibiotic. At sufficient concentrations, it seems like the lipids in the cell membrane would simply dissolve.
Fomite 8y ago
One of the problems with alcohol-based hand sanitizers is that there's a war between "Kills Bacteria" and "Demolishes Your Hands" - one of the major problems in hospitals is compliance, and the harsher the alcohol concentration, the harder it is to get people to use it.
notanote 8y ago
A 70% solution is considered the most effective. Higher concentrations of alcohol (over 90% especially) evaporate more quickly, reducing contact time. Also, they work too quickly. By coagulating the outer proteins of bacteria instantly, they form a protective layer that actually stops the alcohol from penetrating further.
- mmt 8y ago
  Although I agree that over 90% is less effective (and your explanation is clearer than mine [1]), do you have a reference for 70% (and is it w/w or v/v?) is the most effective? Last I read up on it, I found the number to be closer to the European hospital standard of 85%, although I don't have the reference in my bookmarks, nor do I recall if it was reflect of scientific consensus, if one even exists on the topic. [1] https://news.ycombinator.com/item?id=17684070 https://news.ycombinator.com/item?id=17684070
ars 8y ago
> Or is it possible that bacteria could evolve resistance right up to 100%? Adding some water to alcohol kills more bacteria than pure alcohol. See here: https://blog.gotopac.com/2017/05/15/why-is-70-isopropyl-alcohol-ipa-a-better-disinfectant-than-99-isopropanol-and-what-is-ipa-used-for/ https://blog.gotopac.com/2017/05/15/why-is-70-isopropyl-alco...

hcurtiss 8y ago

It’s not like an antibiotic. At sufficient concentrations, it seems like the lipids in the cell membrane would simply dissolve.

Fomite 8y ago

One of the problems with alcohol-based hand sanitizers is that there's a war between "Kills Bacteria" and "Demolishes Your Hands" - one of the major problems in hospitals is compliance, and the harsher the alcohol concentration, the harder it is to get people to use it.

notanote 8y ago

A 70% solution is considered the most effective. Higher concentrations of alcohol (over 90% especially) evaporate more quickly, reducing contact time. Also, they work too quickly. By coagulating the outer proteins of bacteria instantly, they form a protective layer that actually stops the alcohol from penetrating further.

mmt 8y ago
Although I agree that over 90% is less effective (and your explanation is clearer than mine [1]), do you have a reference for 70% (and is it w/w or v/v?) is the most effective? Last I read up on it, I found the number to be closer to the European hospital standard of 85%, although I don't have the reference in my bookmarks, nor do I recall if it was reflect of scientific consensus, if one even exists on the topic. [1] https://news.ycombinator.com/item?id=17684070 https://news.ycombinator.com/item?id=17684070

ars 8y ago

> Or is it possible that bacteria could evolve resistance right up to 100%? Adding some water to alcohol kills more bacteria than pure alcohol. See here: https://blog.gotopac.com/2017/05/15/why-is-70-isopropyl-alcohol-ipa-a-better-disinfectant-than-99-isopropanol-and-what-is-ipa-used-for/ https://blog.gotopac.com/2017/05/15/why-is-70-isopropyl-alco...