Chemical communication is a widespread phenomenon in the natural world, influencing everything from insect mating rituals to mammalian social hierarchies. The idea that humans might also communicate through subtle, airborne chemical signals, much like other animals, has long been a source of popular intrigue. This concept suggests our bodies release compounds capable of triggering specific, unconscious responses in others. The scientific community approaches the question of human pheromones with significant caution and debate. While humans emit a complex array of scent molecules, establishing that any meet the rigorous definition of a true pheromone is an ongoing challenge.
What is a True Pheromone?
The term pheromone was coined in 1959 to describe chemical signals exchanged between members of the same species that elicit a specific reaction. A strict scientific definition requires the chemical to trigger an innate, predictable physiological or behavioral response in the recipient. This response must be involuntary and unconscious, meaning the recipient does not need to learn the signal’s meaning for it to be effective. Pheromones are distinct from general odorants, which are consciously smelled and whose meaning is often learned or context-dependent.
These chemical messengers typically signal anonymously to any member of the species, rather than providing a unique individual “scent fingerprint.” Pheromones are often categorized by the type of response they cause, such as “releaser” pheromones that cause an immediate, stereotyped behavioral reaction. Other types, like “primer” pheromones, cause a slower, developmental, or endocrine change, such as influencing the onset of puberty or estrous cycles. The identification of a true pheromone requires a multi-step process, including demonstrating a measurable response, isolating and synthesizing the molecule, and confirming the molecule alone causes the original effect at natural concentrations.
Chemical Candidates in Humans
Research into human chemical communication has focused heavily on a few naturally occurring steroid derivatives found in sweat and other bodily fluids. The two most frequently studied compounds are Androstadienone (AND) and Estratetraenol (EST), related to the sex hormones testosterone and estrogen, respectively. Androstadienone is a testosterone metabolite found in male sweat and semen. Estratetraenol is a compound found in female urine and is structurally similar to estrogen.
These molecules were initially proposed as potential human pheromones at a 1991 conference, an event notably sponsored by a corporation with commercial interests in the field. Studies have suggested that Androstadienone may affect mood and physiological arousal in women, while Estratetraenol might influence autonomic arousal in men. However, scientific skepticism remains high because these substances have not been isolated through the rigorous bioassay-led approach required to prove a pheromone. Furthermore, the concentrations used in laboratory studies are often significantly higher than what a person would naturally be exposed to in a real-world social setting.
The Specialized Detection System
In most mammals that rely on pheromones, a specialized structure called the vomeronasal organ (VNO) handles their detection. This paired organ is located at the base of the nasal septum and is part of the accessory olfactory system. Unlike the main olfactory system, which projects to the cortex for conscious smell perception, the VNO sends signals directly to brain areas like the amygdala and hypothalamus, which control emotion and hormone release.
In humans, the presence and functionality of the VNO are matters of long-standing debate. While the structure is consistently present in the human fetus, its fate in adults is uncertain. Anatomical and molecular genetic studies suggest that the VNO in adult humans is likely vestigial or non-functional for chemoreception. Humans specifically lack the accessory olfactory bulb, and the genes that code for the specific receptor proteins used in functional VNOs in other mammals have mutated and are inactive. This anatomical deficiency is a major reason why the scientific consensus questions the existence of true, VNO-detected pheromones in humans.
Behavioral and Social Impact
Despite the lack of a definitively identified human pheromone, chemical signals clearly play a role in human social and physiological responses. The most well-known phenomenon is the McClintock effect, which proposed that women living in close proximity might experience synchronized menstrual cycles. While early research suggested odorless compounds from underarm secretions could influence the cycle, the validity of menstrual synchrony is now widely questioned due to methodological flaws and failure to replicate findings consistently.
Other studies have shown that exposure to certain chemical compounds can influence mood or the perception of gender. For instance, some research indicated that women exposed to Androstadienone rated male faces as more attractive, though double-blind trials have failed to confirm these chemicals increase general attractiveness. Commercial products often advertise these compounds as powerful “sex pheromones” to boost appeal, but the lack of robust, replicated evidence means these claims remain scientifically unsupported. The subtle influences observed are better classified as modulators of social cues rather than true, behavior-releasing pheromones.