Valentine's Day often brings hopes of romance, sometimes spurring aspiring Romeos or Juliets to seek assistance from products marketed as human pheromones.
It's just wishful thinking, according to George Preti, PhD and Charles Wysocki, PhD, scientists at the Monell Chemical Senses Center.
'We still have much to learn about pheromonal communication in humans. However, based on what we do know, human pheromones do not act as sex attractants,' says Wysocki, a behavioral neuroscientist. 'Effects of pheromones on adult human social behavior have never been documented in a controlled peer-reviewed setting.'
First identified in insects, pheromones are chemical substances secreted to the environment by an individual that cause a programmed response in a second individual of the same species. By definition, responses to pheromones are involuntary.
Insect pheromones can elicit well-defined responses, including overt displays of attraction and sexual behavior. Bombykol, the first chemical compound identified as a pheromone, is secreted by the female silkworm moth to entice males as potential mates.
'The general term pheromone is often linked to images of specific, rapid response and sexual attraction,' notes Preti, an organic chemist. 'Actually, pheromones are divided into classes that are defined by characteristics of the responses.'
Chemical signals that elicit immediate behaviors are described as releaser pheromones. Examples of releaser pheromones include mating attractants such as bombykol and danger-signaling alarm pheromones released by insects and mammals, which can elicit aggressive behavior or rapid withdrawal.
Primer pheromones have long-term physiological effects on the recipient, perhaps affected through changes in gene expression. Primer effects often target reproductive or developmental processes, as in the case of chemicals released by honeybee queens to stop ovary development of worker bees.
Signaler pheromones provide information, such as an individual's sex or age. And, scientists are beginning to believe that certain primate pheromones may also affect a recipient's mood; these have been labeled modulator pheromones.
To be classified as a pheromone, a chemical or small set of chemicals must be obtained from one member of a species, structurally characterized, and then be shown to produce a reliable involuntary response in other members of the same species. Chemicals isolated from bodily secretions such as sweat, saliva or urine of several mammalian species, including swine and hamsters, have been validated as pheromones.
However, the chemical identities of human pheromones remain elusive. Preti comments, 'To date, no scientifically rigorous study using human secretions has led to the isolation and chemical identification of a true human pheromone.'
On the other hand, detailed studies have demonstrated pheromonal responses in humans, implying that humans do in fact produce and respond to pheromones. For example, Preti and Wysocki established that unidentified chemicals in human male underarm extracts can affect female reproductive hormone secretion (primer pheromone effect) and mood (modulator pheromone effect).
But Wysocki notes, 'Because human responses to pheromones and other chemical signals are influenced by our past experiences, context and other sensory inputs, it is unlikely that pheromones can cause the same type of involuntary attractant response in humans that is seen in the silkworm moth.'