A shortened form of “surface active agent.” This class of chemicals reduces surface tension; thereby allowing oil and water to form stable mixtures.

Surfactants are amphiphilic molecules that have hydrophobic and hydrophilic parts. The hydrophobic tail is a hydrocarbon, fluorocarbon, or siloxane. Surfactants are typically classified based on their polar head as the hydrophobic tails are often similar. If the head group has no charge, the surfactant is called non-ionic. If the head group has a negative or positive charge, it is called anionic or cationic, respectively. If it contains both positive and negative groups, then the surfactant is called zwitterionic.

Source: Biolin Scientific