Medical plastic oxygen masks are used primarily by medical care providers for oxygen therapy because they are disposable and so reduce cleaning costs and infection risks. Mask design can determine accuracy of oxygen delivered with many various medical situations requiring treatment with Oxygen. Oxygen is naturally occurring in room air at 21% and higher percentages are often essential in medical treatment. Oxygen in these higher percentages is classified as a drug with too much oxygen being potentially harmful to a patients health resulting in oxygen dependence, over time, and in extreme circumstances patient blindness. For these reasons oxygen therapy is closely monitored. Masks are light in weight and attached using an elasticated headband or ear loops, they are transparent allowing the face visible for patient assessment by healthcare provider and reducing a sensation of claustrophobia experienced by some patients when wearing an oxygen mask. The vast majority of patients having an operation will at some stage wear an oxygen mask, they may alternatively wear nasal cannula but oxygen delivered in this way is less accurate and restricted in concentration.