Purpose. Surfactant reduces the surface tension of fluid in the lungs and helps make the small air sacs in the lungs (alveoli) more stable. This keeps them from collapsing when an individual exhales.or example, if a drop of detergent is added to a drop of water, the detergent reduces the surface tension and the drop of water flattens out. In the lungs, surfactant reduces the surface tension and helps to maximize the surface area available for gas exchange.