A biosurfactant is a natural surfactant: a chemical produced by a living organism that decreases the surface tension of water.

For instance, biosurfactants on the lungs of human babies and late-term fetuses keep their lungs from collapsing. Fetuses start producing lung surfactant in their last trimester.

Earlier-term fetuses have trouble surviving in part because their lungs tend to collapse due to the surface tension of water on their alveoli prevents them from expanding after the infant has exhaled. The medical name for this problem is respiratory distress syndrome (RDS). In 1990, the U.S. Food and Drug Administration approved a form of surfactant therapy that has saved the lives of many premature infants.

One of the surfactant agents for premature infants is marketed under the name Exosurf Neonatal. It comes as a powder that physicians mix with water and blow into the babies' lungs.

Other biosurfactants, which are often rhamnolipids, are used for a wide variety of industrial applications. They are sometimes produced by engineered bacteria and are used as emulsifiers and solvents in: