Why 70% EtOH for cleaning?

Aydemir Akin akin at sage.cc.purdue.edu
Mon Jun 19 15:59:30 EST 1995

In article <3rrkik$7fk at wumpus.cc.uow.edu.au>, ana25 at wumpus.cc.uow.edu.au
(Neil Anthony Armstrong) wrote:

> I was told as an undergard that the alcohol had a better chance of
> the bacteria when it was mixed with 30% water.The higher water content 
> facilitated the alcohol uptake by the bacteria.

>Subject: Why 70% EtOH for cleaning?
>Date: Thu Jun 01 04:14:57 EST 1995
>Organization: University of Newcastle, AUSTRALIA
>Lines: 11

>Hi all,

>I have a very general question.  I was told that 70% EtOH is more 
>effective than 95% EtOH for sterlizing and cleaning surfaces.  
>Tradition of course is to use 70% to wipe hoods etc.  I had assumed 
>70% was used just to cut costs. Can anybody out there tell me why 
>70% is used? Just curious really.
>Allen Black
>Univ. of Newcastle
>mdcabl at cc.newcastle.edu.au


The mechanis of antibactrial action of alcohols (ethanol, isopropanol)
is due to their ability to denature intracellular soluble proteins and
to depress bacterial surface tension.  When they are used in high
concentrations (e.g. 95%), they tend to create a layer that is 
impermeable by alcohol on the bacterial wall.  Thus, their potency 
is reduced.  For example, to achieve the same antibacterial effect of 70%
ethanol (10 sec treatment), you would need at least 5 min treatment with
100% ethanol.  Prolonging the treatment time infact may not increase the
bactericidal effect. 

Ethanol 70% (w:w) or 78% (v:v) and isopropanol 50% (w:w) are the most 
commonly used concentrations of alcohols for antisepsis.  8-)

akin at sage.cc.purdue.edu

Aydemir Akin
1175 Animal Disease Diagnostic Lab
Purdue University
West Lafayette, IN 47907-1175

Aydemir Akin, D.V.M.

akin at sage.cc.purdue.edu

1175 Animal Disease Giagnostic Lab
Purdue University
West Lafayette, IN 47907-1175

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