Exposure to oxygen at a high FIO2 can result in substantial damage to several organ systems. In contrast, low-flow oxygen is generally quite safe. Although there have been reports of lung tissue injury with low-flow oxygen, the benefits of this therapy in appropriately selected individuals clearly outweighs the small risks. Elevations in PaCO2 occur in some COPD patients receiving low-flow oxygen and appear to be related to changes in ventilation-perfusion matching in the lung and carbon dioxide transport in the blood stream rather than to reductions in respiratory drive as previously thought. The effect is generally small in magnitude and is not progressive in response to oxygen therapy alone. Nonmedical hazards such as frostbite and fire related to oxygen equipment have been described but are unusual. Minor problems such as skin rash or nasal irritation in those using low-flow oxygen are usually easily handled with topical treatments. Social and psychological problems, resulting from a perceived stigma of wearing oxygen may lead to social isolation of the patient and should be addressed with appropriate counseling and education.