New research from the University of Tokyo finds that three specific chemical compounds in women’s body odor increase during ovulation, lowering men’s biological stress levels and boosting perceptions of facial attractiveness.
Published on July 28, 2025, in the journal iScience, the study analyzed 84 armpit odor samples collected from 21 female donors across four distinct stages of the menstrual cycle. Human communication relies on much more than spoken words and visual body language. Emerging trends in olfactory neuroscience show that unconscious chemical signals, known as chemosignals, quietly shape human mood, threat detection, and social bonding through 400 specialized olfactory receptors in the nose.
“Furthermore, those compounds were found to relax the male subjects, compared to a control, and even suppressed the increase in the amount of amylase (a stress biomarker) in their saliva,” explained Professor Kazushige Touhara, the study’s senior author. “These results suggest that body odor may in some way contribute to communication between men and women.”
The Quiet Broadcast Behind Human Attraction
Across the animal kingdom, shifting female body scents act like an invisible biological broadcast that signals peak fertility and reshapes male behavior.
In non-human primates such as common marmosets, female ovulatory odors trigger immediate exploratory behavior and measurable spikes in male testosterone. Humans share a subtle version of this evolutionary wiring, even if modern life masks it with soap and cologne. Previous endocrine studies demonstrate that men exposed to female ovulatory body odors experience elevated testosterone and reduced cortisol stress hormones, whereas oral contraceptives flatten these cyclic scent fluctuations.
Until recently, however, the exact molecular recipe behind this human emotional shift remained a scientific mystery. Researchers knew men consistently rated women’s natural scent as more pleasant during their fertile window, yet the specific chemical compounds driving that reaction hadn’t been isolated.
Related: 6 Scents Men Love on Women and 5 Fragrances That Turn Them Off
Tracking Cycle Chemistry Inside The Tokyo Study
Pinpointing the exact molecules that fluctuate during ovulation required over a month of intensive biological tracking per donor and high-precision chemical analysis.
Researchers at the University of Tokyo’s Department of Applied Biological Chemistry and the International Research Center for Neurointelligence tracked 21 women across their menstrual, follicular, ovulatory, and luteal phases.
“The most difficult part of the study was to determine the axillary (armpit) odor profile within a woman’s menstrual cycle,” noted first author Nozomi Ohgi. “Of particular difficulty was scheduling more than 20 women to ensure that axillary odors were collected at key times during their menstrual cycles.”
To guarantee precision across all 84 samples, the research team verified each donor’s cycle stage using luteinizing hormone (LH) surges, basal body temperature, and salivary estradiol and progesterone levels. Because emotional tension alters human sweat chemistry, researchers also administered the State-Trait Anxiety Inventory (STAI) to filter out stress-induced odors.
Donors wore sterile gauze pads under their arms overnight at home for 12 hours to capture natural baseline compounds. “It took more than one month per participant to complete the collection within the menstrual cycle, so very time consuming,” Ohgi added.
Three Scent Molecules That Melt Away Male Stress
Using gas chromatography-mass spectrometry (GC-MS), the Tokyo team isolated three specific volatile compounds that surge during ovulation and actively calm the male nervous system. At the exact same time, sharp acidic components that give baseline sweat a sour, vinegar-like note dropped significantly during the fertile window.
Each of the three isolated ovulatory molecules contributes a distinct chemical profile that softens harsh baseline body odor. In blind sensory evaluations, male participants sniffed a model armpit odor blended with these three ovulatory compounds alongside blank controls. Because the men received zero hints about what they were smelling, psychological guesswork and expectation bias were completely ruled out.
The chemical trio neutralized unpleasant baseline sweat and prevented spikes in salivary amylase, an enzyme that surges in saliva during acute sympathetic stress. Even more remarkably, men who inhaled the ovulatory blend rated accompanying photographs of women’s faces as significantly more attractive and feminine, showing that nasal cues directly influence visual judgment.
Why Scientists Call These Signals Pheromone-Like
Despite their calming and attraction-boosting effects, scientists caution that these three ovulatory molecules aren’t officially classified as human pheromones yet.
In pop culture, pheromones often get treated like magic love potions in perfume ads. Real neurobiology holds a much stricter bar for that label. “The classical definition of pheromones is species-specific chemical substances that induce certain behavioral or physiological responses,” Touhara clarified.
Because the Tokyo experiment focused on human emotional and physiological reactions rather than testing whether these molecules work exclusively on humans, the team calls them “pheromone-like” compounds.
Why Hidden Scent Signals Matter For Mental Health
Image Credit: 9dreamstudio via 123RF
Understanding how natural body odors lower stress biomarkers opens exciting new frontiers in neuroscience, social communication, and psychiatric care.
Related computational studies from Touhara’s laboratory demonstrate that 3D molecular shapes and receptor activation profiles predict human odor perception with high precision, showing how the brain translates invisible chemistry into emotion.
Next, the Tokyo researchers plan to expand their participant pool to test whether individual genetic variations change how men respond to ovulatory scents. The team also plans to run functional brain scans to watch emotion and memory centers, such as the amygdala and hippocampus, respond in real time to these three compounds.
Beyond romance and dating, chemosignaling science is gaining serious momentum in clinical mental health. Neuroscientists are actively investigating how positive human chemosignals could unlock new, non-invasive therapies for social anxiety, phobias, and chronic depression.
The Olfactory Impact Snapshot
Women’s natural body chemistry shifts during ovulation in ways that quietly soothe men’s stress and brighten their social perceptions.
By isolating geranylacetone, myristic acid, and palmitoleic acid across 84 cycle samples, University of Tokyo scientists proved that human scent acts as a subtle emotional bridge. While these molecules remain “pheromone-like” pending species-specificity tests, their ability to suppress salivary amylase and boost facial attractiveness ratings suggests the human nose is a powerful emotional radar.
How might these hidden chemical signals reshape the way modern society views everyday attraction, fragrance habits, and natural stress relief?
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