The term sterile means free of germs, meaning free of microorganisms and viruses.

Sterilization is the procedure used to remove living microorganisms from materials and objects.

When something is sterilized, ideally all microorganisms and spores should die, and all viruses, prions (which are infectiuous proteins), plasmids and other DNA-fragments should be destroyed. This makes the object non-infectious. You cannot get an infection from it.

Sterilization using steam (heating in an autoclave) is the procedure usually used in most laboratories and hospitals. Here you can see the sterilizer being loaded with operatingcontainers, filled with instruments which are to be sterilized. The instruments are heated for 20 minutes at 121 °C or two bars of pressure in steam or for 5 minutes at 134 °C at a pressure of 3 bar. Prions can be destroyed by heating for 18 minutes at 134 °C and 3 bars. The air in the autoclaves is replaced by steam.

After the sterilization process, the containers are removed, and the operating instruments are ready for the next operation. The picture shows an operating container in which the instruments are neatly sorted. Operating containers are not usually used in doctor's offices. The instruments may not be touched after removal from the autoclave, as this once again makes them unsterile. Sometimes the instruments are shrink-wrapped in foil, and can be stored for a short time while remaining sterile. Should the packaging be damaged, the instrument once again becomes unsterile!

Sterile instruments are rendered useless if unsterile packaging is used – here there are also differences in handling. Using disposal items is unproblematic and safe – they are sterilized by the manufacturer and thus germ-free. Here you can see a disposable sterile covering spread out as an underlay before an operation, and the sterile instruments are laid out on it.

Washable linen cloths are sometimes used instead of disposable items, and sometimes they are sterilized in autoclaves, but in not in all doctor's offices. At any rate the cloths are unsterile, because even autoclaves do not remove all germs.