exhale

An exhale, or expiration, is the act of expelling air from the lungs through the nose or mouth. It is one phase of the respiratory cycle, occurring after inhalation. Exhalation helps clear the airways of stale air and carbon dioxide, a metabolic waste product.

In normal breathing, expiration is usually passive. The diaphragm and chest muscles relax, allowing the lungs and chest wall to recoil, which reduces thoracic volume and raises intrapulmonary pressure, pushing air out. During forced expiration—such as during heavy exercise, coughing, or singing—the expiratory muscles, including the abdominal muscles and internal intercostals, actively compress the thoracic cavity to accelerate air removal.

Exhaled air contains carbon dioxide and varying amounts of water vapor and other volatile compounds. Its removal is essential for maintaining blood pH through the bicarbonate buffering system. Exhalation also enables speech and other vocal activities by providing a controllable airstream. In clinical settings, measurements of end-tidal CO2 and other components of exhaled breath help assess ventilation, airway status, and certain metabolic conditions.

In everyday life, exhalation is influenced by posture, fitness, and health. Practices such as diaphragmatic breathing and some forms of meditation emphasize slow, controlled expiration to promote relaxation and reduce stress. Exhalation patterns may be altered in respiratory diseases, such as chronic obstructive pulmonary disease, where expiration can be prolonged and labored.