At what percentage is alcohol effective as a disinfectant?

Alcohol is considered most effective as a disinfectant at a concentration of approximately 70%. This percentage is optimal because it allows for adequate penetration of the alcohol into the cell walls of microorganisms, leading to effective protein denaturation and cell lysis. When alcohol is diluted to this specific concentration, it also retains enough water to slow down the evaporation rate, providing better contact time with pathogens on surfaces and skin.

Using a concentration lower than 70% may not be effective enough to kill microorganisms, while concentrations above 70%, like 90% or 80%, evaporate too quickly and do not provide sufficient time for the antimicrobial effect. Therefore, the 70% concentration strikes the necessary balance for achieving optimal disinfection.