A pheromone is any chemical produced by a living organism that transmits a message to other members of the same species. There are alarm pheromones, food trail pheromones, sex pheromones, and many others. Their use among insects has been particularly well documented, although many vertebrates also communicate using pheromones. Their use by humans is controversial.
Pheromones are a popular device in fiction, including the novel Jitterbug Perfume by Tom Robbins and the film Love Potion Number Nine.
Some commercially-available substances are advertised using claims that the products contain sex pheromones and can act as an aphrodisiac. These claims often lack credence due to an excessive marketing of pheromones by unsolicited e-mail, and their effectiveness has not been demonstrated scientifically.
Nevertheless, a few well-controlled scientific studies have been published demonstrating that humans may use pheromones in some circumstances. The best-studied case involves the synchronization of menstrual cycles among women based on odor cues. Other studies have suggested that people can use odor cues to select mates who are not closely related to themselves.