A Pheromone is a type of chemical that is secreted by a lifeform, pheromones influence the behavior or development of others, usually of the same species, usually functioning as an attractant for the opposite sex.
Locator bombs work by targeting an individual's pheromones. (DS9: "The Nagus")
Orion slave girls have been known to secret a highly potent pheromone that accelerates the metabolisms of males of many species, raising adrenalin production to dangerous levels. It causes aggression and a form of delusion and it makes them succeptable to suggestion. The pheromone causes headaches in Human females and disrupts the sleep cycle of Denobulan males. Vulcans, however, are immune. The pheromones effects are cumulative, the longer exposed the more pronounced the results are. In 2155 Dr. Phlox of the Enterprise NX-01 theorized that the pheromone acts as a defense mechanism against competition. (ENT: "Bound")