This analysis examines the roots of clinical practice regarding oxygen therapy and finds that some aspects have changed very little over the past 200 years. Oxygen is commonly prescribed and administered as a therapy across all healthcare settings, particularly for the treatment and management of respiratory conditions, both acute and chronic. Yet despite its widespread use and recent advances in understanding and guidance, poor practice and controversies regarding its use persist. This historical analysis highlights origins in practice that may suggest where the roots of these fallacies lie, highlighting potential ambiguities and myths that have permeated clinical and social contexts. It can be considered that based on clinical presumptions and speculation the prolific and injudicious use of oxygen was encouraged and the legacy for today’s practice seeded. The conjectures proposed here may enable modern day erroneous beliefs to be confronted and clinical practice to move on.