How do alcohols and aldehydes destroy the plasma membranes of bacteria?
Alcohols are dehydrating - they remove water from the cell. And since cells need water to survive, this is lethal to bacteria. However, in order to work effectively, an alcohol needs the proper amount of time to penetrate the cell membrane of the bacterium. If the percentage of alcohol is too high, it will evaporate before entering the cell. Too low, and it will enter the cell but not be lethal. 70% alcohol turns out to be the most effective concentration for use as a surface disinfectant with many different types bacteria.