When diluted below what percentage does alcohol lose its efficiency?

Alcohol, particularly isopropyl or ethyl alcohol, is widely used as a disinfectant and antiseptic. The effectiveness of alcohol as a microbial agent is significantly influenced by its concentration. It is generally accepted that a solution of 70% alcohol is optimal for disinfection purposes. At this concentration, the presence of water slows the evaporation of alcohol, allowing it to remain in contact with pathogens long enough to effectively penetrate their cell walls and denature their proteins.

Diluting alcohol below 70% compromises its ability to effectively kill bacteria and viruses. For instance, at 60% alcohol concentration, while some antimicrobial properties remain, they are not sufficient to ensure a high level of efficacy for disinfection. Therefore, 70% alcohol is regarded as the threshold for maintaining its efficiency as a disinfectant, while lower concentrations lose their potency significantly in their ability to terminate microorganisms.