Humans breathe out carbon dioxide (CO2). It is a natural byproduct of cellular respiration, the process by which our bodies convert glucose and oxygen into energy. During this metabolic process, carbon dioxide accumulates in the blood and is then expelled from the body through the lungs when we exhale. Along with oxygen intake, the balance of carbon dioxide is crucial for maintaining the body’s pH level and overall homeostasis. Increased levels of carbon dioxide in the atmosphere can also contribute to climate change, highlighting the importance of understanding gas exchanges in both human biology and environmental science.