A pheromone was a chemical secreted by a lifeform, that had an effect on another lifeform.
Locator bombs worked by homing in on an individual's pheromones. (DS9: "The Nagus")
Orion slave girls secreted a highly potent pheromone that accelerated the metabolisms of males of many species, raising adrenaline production to dangerous levels. It caused aggression and a form of delusion that made them susceptible to suggestion. The pheromone caused headaches in Human females and disrupted the sleep cycle of Denobulan males; Vulcans, however, were immune. The pheromone's effects were cumulative; the longer one was exposed, the more pronounced the results. In 2154, Doctor Phlox of Enterprise NX-01 theorized that the pheromone acts as a defense mechanism against competition. (ENT: "Bound")
In the novelization of "Star Trek: The Motion Picture", pheromones are the reason for the Deltans being viewed as sexually attractive by other species.
Denobulan females emitted powerful pheromones during their mating season. Male Denobulans often became combative during this time, and mating could require medical supervision. (ENT: "Dear Doctor", "A Night in Sickbay", "Bounty")
In 2370, Captain Picard used pheromones from Deanna Troi to lure Worf while they all suffered from Barclay's Protomorphosis Syndrome. (TNG: "Genesis")
Ramurans produced pheromones that prevented the formation of long-term memory engrams in other species they interacted with. (VOY: "Unforgettable")
In 2375, One, an advanced Borg drone with 29th-century technology, detected an elevated pheromonal response in a USS Voyager crew member, indicating that she was afraid of him. (VOY: "Drone")
Queen Arachnia's pheromone vial
In The Adventures of Captain Proton holoprogram, the character of Queen Arachnia had, in her possession, a small vial of her pheromones, which she could use to seduce and control others. Kathryn Janeway, as Arachnia in 2375, used these pheromones against the character of Lonzak. (VOY: "Bride of Chaotica!")
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