Asepsis is the state of being free of contamination of bacteria, viruses, parasites or fungus, or where precautions have been taken to prevent the transmission of such disease causing agents. In medicine, it is the technique by which an environment or device is treated to remove or destroy such disease causing agent, or to ensure that they do not exist in the first place.
In practical terms, the only way to render an environment completely free of disease causing agents is to use ionizing radiation, which is dangerous to human health. As such, environments or things that must be aseptic are made as disease free as possible and additional precautions are taken to prevent transmission of the disease causing organisms that remain.
The most important aseptic environment in a hospital is the operating room. These are made of materials that do not harbor disease organisms easily (such as metal and ceramics), and are cleaned between uses of the room. Personnel who go into an operating room follow strict hygiene procedures, including carefully washing hands and arms, and wearing freshly laundered gowns and one-use surgical masks. The air in an operating room is carefully filtered before being allowed in the room, and is filtered again on the way out to prevent the transmission of disease.
Medical instruments are sterilized by using an autoclave, a device that uses steam at extreme pressure to raise the temperature to well over the normal boiling point of water.
Most one use items, such as tonge depressors, bandages, needles and any other thing likely to touch a patient are created in an aseptic environment and sealed before use.