Pheromones are chemical signals released by organisms that can influence the behavior or physiology of others within the same species. In human interactions, “armpit pheromones” have emerged as a fascinating area of scientific inquiry. These subtle chemical communications, often operating beneath conscious awareness, represent a potential layer of biological influence on our social lives, suggesting our bodies might communicate beyond spoken words or visible cues.
What Pheromones Are and How They Differ from Odor
Pheromones are chemical compounds that elicit an innate behavioral or physiological response in members of the same species. Unlike regular body odor, which largely results from bacterial breakdown of sweat, pheromones function at a subconscious level. While body odor is consciously perceived and influenced by hygiene or diet, pheromone effects are often imperceptible to our conscious sense of smell. Armpit sweat contains specific compounds, such as androstadienone (a testosterone metabolite found in male semen and armpit secretions) and estratetraenol (an estrogen found in female urine), which researchers investigate as potential human pheromones.
These compounds are secreted by apocrine sweat glands, concentrated in areas like the armpits. The “fermentation hypothesis,” proposed in the 1970s, suggests that microbes in these warm, damp, low-oxygen areas ferment nutrient-rich secretions into chemical signals. This indicates bacteria in our underarms may play a role in social interactions by producing these signals.
The Influence of Armpit Pheromones on Human Behavior
Armpit pheromones are hypothesized to play subtle roles in human social interactions, influencing attraction, mood, and social signaling. Studies suggest that certain compounds in female body odor increase during ovulation. When mixed with armpit odor samples, men rated the scent as more pleasant and viewed associated images of women as more attractive and feminine. These scents also appeared to reduce stress, based on lower levels of the biomarker amylase in saliva. While not definitive proof of human pheromones, these findings indicate that smell might quietly influence how people relate to each other.
Male axillary extracts have been shown to affect the pulsatile secretion of luteinizing hormone (LH) and mood in women. These extracts, containing primer pheromones, can advance the next LH peak, reduce tension, and increase relaxation. Exposure to androstadienone in women has also been suggested to promote attractiveness ratings of potential mates.
One notable research area is the “McClintock effect,” which proposes that women living in close proximity may experience synchronization of their menstrual cycles. While controversial, some studies explore whether human pheromones from armpit secretions mediate this effect. For instance, odorless compounds from the armpits of women in the late follicular phase have accelerated the preovulatory surge of luteinizing hormone in recipient women, shortening their cycles. Conversely, compounds collected during ovulation delayed the LH surge and lengthened cycles.
How Pheromones Are Detected
Humans primarily detect these chemical signals through the conventional olfactory system, our sense of smell. Even if cues are below conscious awareness, the brain can still process these subtle chemical messages. For instance, exposure to androstadienone affects autonomic arousal in men and increases “male” responses in heterosexual women when evaluating point-light walkers, which are collections of dots representing human movement.
The vomeronasal organ (VNO), also known as Jacobson’s organ, is a chemosensory organ at the base of the nasal septum that specializes in detecting pheromones in many animals. While the VNO develops in human embryos, its functional role in adult humans for pheromone detection is highly debated and largely unproven. In adults, vomeronasal cavities may be observed, but they generally lack sensory neurons and nerve fibers, and genes for vomeronasal receptor proteins are often nonfunctional.
Current Scientific Understanding
The scientific understanding of human armpit pheromones is complex and often controversial. While some studies suggest a potential influence of compounds like androstadienone and estratetraenol on human behavior and physiology, definitive proof of human pheromones remains elusive. The cosmetics industry promotes the idea that adding pheromones to products can enhance attraction, but current research indicates that if humans are affected, their specific identity and role are not yet fully understood.
Challenges in human pheromone research include isolating specific compounds, controlling for confounding variables like diet and stress, and establishing clear behavioral or physiological outcomes. Studies often have small sample sizes and may be influenced by publication bias, where positive results are more likely to be published. Despite these challenges, the field continues to evolve, with ongoing discoveries suggesting that subtle chemical cues from body odor may contribute to communication between individuals.