Inhalation is the process of breathing in air or other gases into the lungs. It occurs when the diaphragm and intercostal muscles contract, causing the chest cavity to expand and creating a negative pressure that draws air in. This process is essential for respiration, allowing oxygen to enter the bloodstream and carbon dioxide to be expelled from the body. Inhalation can also refer to the intake of substances, such as medication or smoke, through the respiratory system.