The primary gas that humans exhale is carbon dioxide (CO2). During respiration, the body takes in oxygen from the air, which is used in cellular processes to produce energy. As a byproduct of this process, carbon dioxide is generated and must be expelled from the body. The lungs play a critical role in this gas exchange, where oxygen is absorbed into the bloodstream, and carbon dioxide is released during exhalation. Maintaining a balance of these gases is essential for healthy bodily function.