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Damage to the lung’s air sacs—called alveoli—causes ARDS. Fluid from tiny blood vessels leaks through the damaged walls of the air sacs and collects, limiting the lungs’ normal exchange of oxygen and carbon dioxide. The damage also causes inflammation that leads to the breakdown of surfactant —a liquid that helps keep your air sacs open.
The air sacs may become damaged as a result of an illness, such as a lung infection, or breathing in smoke. Other illnesses or injuries may trigger inflammation that damages the air sacs. To understand ARDS, you may also want to read about how the lungs work.