The gas that humans exhale after respiration is carbon dioxide (CO2). During the process of respiration, oxygen is inhaled into the lungs and transported to cells throughout the body, where it is utilized for energy production in a process called cellular respiration. As a byproduct of this energy generation, carbon dioxide is produced and then transported back to the lungs, where it is expelled from the body when exhaling. The regulation of carbon dioxide levels is critical for maintaining the body’s acid-base balance and is closely monitored by the respiratory system to ensure proper functioning.