Steam sterilization primarily achieves sterilization through which mechanism?

• A. Moist heat under pressure
• B. Dry heat by hot air
• C. Chemical vapor from formaldehyde
• D. Ultraviolet radiation

Answer: (A)

Moist heat under pressure is the mechanism. Steam transfers heat rapidly and deeply because of the moisture, and the applied pressure raises the temperature above 100°C, typically around 121°C, allowing complete penetration into wrapped packs and instrument lumens. This heat–moisture combination denatures and coagulates cellular proteins, rapidly killing bacteria, viruses, and spores. Dry heat requires much higher temperatures and longer times because heat transfer without moisture is slower. Chemical vapor sterilization uses chemical vapors, not steam, while ultraviolet light kills surface microbes but doesn’t penetrate into instruments or wraps.