Why 70% EtOH for cleaning?

Brick Ayola abrick at mailhost.tcs.tulane.edu
Fri Jun 2 14:17:47 EST 1995

On 1 Jun 1995 mdcabl at cc.newcastle.edu.au wrote:
> 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.

The bactericidal effects of EtOH result from rapid coagulation of 
protein. 70% EtOH reduces the surface tension of bacterial cells  better 
than absolute. It is believed that absolute EtOH precipitates the 
protoplasm at the periphery of the cell retarding penetration. 
Isopropyl has slightly better bactericidal activity by 
virtue of an even greater ability to reduce surface tension. Alcohol also 
has virucidal activity (enveloped), but a negligible effect on spores or 

from: AMA Drug Evaluations Annual 1995.

Brick Ayola, Ph.D.
Tulane School of Medicine

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