Pheromones are secreted or excreted chemosignals that trigger social and sexual responses in members of the same species; chemicals capable of acting as hormones outside the secreting organism to affect behaviour or physiology in others. Pheromones may be present in all bodily secretions. Multiple types of pheromones exist, alarm pheromones, food trail pheromones, signaller, modulator, primer, territorial, trail and sex pheromones. Releaser pheromones often prompt an immediate behavioural reaction and have received the greatest attention in animals.
In many species pheromones are detected by regular olfactory membranes, although three families of vomeronasal receptors exist, V1Rs, V2Rs, and V3Rs. All are G protein-coupled receptors but are only distantly related to the receptors of the main olfactory system. In humans and other animals, trace amine-associated receptors (TAARs) in the olfactory epithelium may function as a class of pheromone receptors. The role of pheromones in humans remains uncertain.