The primary gas expelled by the lungs is carbon dioxide (CO2). When oxygen is inhaled into the lungs, it is transported to the bloodstream and utilized by the body for cellular respiration, a process that produces energy. During this process, carbon dioxide is generated as a waste product and transported back to the lungs for exhalation. This exchange of gases—oxygen in and carbon dioxide out—is vital for maintaining proper respiratory function and overall metabolic health. Impaired gas exchange can lead to respiratory issues and other health complications, highlighting the importance of maintaining lung health through various lifestyle choices.