A device that covers the nose and mouth to enable inhalation anaesthetics (see ANAESTHESIA) or other gases such as oxygen to be administered. It is also a covering for the nose and mouth of surgeons and nurses to ensure that antiseptic conditions are maintained during surgery, when dressing a wound or nursing a patient in conditions of isolation. The term mask is also applied to the expressionless appearance that occurs in certain disorders – for example, in PARKINSONISM.