A surfactant is a chemical that lower the surface tension between two different substances. Detergent is a common example - it lowers the surface tension of water allowing the water to dissolve fats in addition to other materials that exist in a water solutions.
The properties of surfactants are being examined in medicine to deal with the delivery of certain types of pharmaceuticals. For example, surfactants are used to break up the air molecules that surround small particles of sulfur or charcoal so they can be dissolved and suspended in a liquid medium instead of clumping together or sitting on the surface of the liquid. They can also be applied to bandages and gauze so that medications will be absorbed by the fibers.
However, they are also commonly used to dislodge dirt from wounds, and in lotions and sprays so they sit better on the skin.