Oxygen therapy or supplemental oxygen is the use of oxygen for medical purposes. It’s used by around 1.5 million people in the United States and can alleviate symptoms associated with a variety of respiratory conditions such as chronic obstructive pulmonary disease (COPD), asthma, and cystic fibrosis. Although oxygen therapy is a common medical treatment, there seems to be a lot of confusion around what it is, how it works, and why it’s so important.