Negative feedback mechanisms control breathing rates. Changes in carbon dioxide and/or oxygen concentrations in the blood drive these mechanisms. The first stimulus that triggers an increase in the breathing rate is high carbon-dioxide levels.

Chemical receptors found in the medulla oblongata of the brain trigger a message. These chemoreceptors signal the diaphragm and intercostal muscles of the rib cage to increase breathing movements. The result is a greater exhalation of carbon dioxide. This gives a lowered blood CO₂ concentration—a negative feedback response.

Oxygen chemoreceptors are found in the aorta and carotid arteries. These chemoreceptors respond to low oxygen levels even if carbon-dioxide levels in the blood are normal. For example, this might occur at high altitudes. The negative feedback response would again be controlled by the medulla oblongata, which would again stimulate an increase in breathing movements and blood-oxygen levels would increase.