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Why does rising carbon dioxide in the blood create an urge to breathe?

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Blood plasma — blood Blood sediment in test tubes, showing plasma (clear fluid), red blood cells (red), and the release of hemoglobin into the surrounding plasma (pink).

Rising levels of carbon dioxide in the blood serve as the primary stimulus for breathing, rather than oxygen levels. As a metabolic waste product, carbon dioxide is acidic; its accumulation lowers the pH of the blood and surrounding fluids.1

This increase in acidity and carbon dioxide tension is detected by specialized sensors called chemoreceptors. Central chemoreceptors, located near the ventral surface of the medulla in the brain, respond to these changes by signaling the body to increase the rate and depth of ventilation. Additionally, peripheral chemoreceptors—specifically the carotid bodies and aortic bodies—monitor arterial blood and further stimulate respiratory neurons when carbon dioxide levels rise.213

This physiological feedback loop is essential for maintaining blood pH and gas balance. The "irresistible" urge to breathe experienced when holding one's breath is the direct result of this rising carbon dioxide tension, which forces the body to accelerate the elimination of the gas through the lungs.1