Alcohol used as a disinfectant is typically what percent?

• A. 50%
• B. 70%
• C. 60%
• D. 90%

Answer: (B)

Alcohol’s ability to disinfect relies on having enough water to help the substance penetrate cells and denature proteins. A 70 percent solution hits the right balance: it’s concentrated enough to kill microbes quickly, yet contains enough water to allow effective diffusion and thorough protein coagulation inside cells. Higher concentrations like 90 percent dry out the surface and limit penetration, making them less effective. Lower concentrations around 50–60 percent don’t denature proteins as efficiently and take longer to achieve kill. For typical disinfection, especially on skin and surfaces in clinical settings, 70 percent is the standard choice.