Decoding Female Axillary Odor

The Al Bundy theory of human pheromones

A new study from Tokyo University is a monster—a big, complicated, multi-stage project on female axillary odors across the menstrual cycle. Like Godzilla Minus One, it captures traditional elements (odor collection using gauze pads) while adding novel angles (GC-mass spec chemical analysis). The result is a new spin on an old story—although I’m not sure it’s one that the authors intended.

Collecting the original sweat samples was anything but easy. “The most difficult part of the study was to determine the axillary (armpit) odor profile within a woman’s menstrual cycle,” said Nozomi Ohgi, the study’s first author and a graduate student in Touhara’s lab.

Nozomi-san isn’t kidding—the collection of odor samples was super-meticulous. Twenty-one women provided samples from four precisely timed phases of the cycle. These were assessed by male raters for odor pleasantness and intensity. Samples across all four phases were perceived as minimally intense and mildly unpleasant, with the ovulatory phase least unpleasant—no surprises there.

In a new twist, additional odor samples were collected for chemical analysis using polydimethylsiloxane membranes, which apparently are more efficient than gauze at capturing the long-chain and unsaturated fatty acids found in the armpit. Using GC-mass spec analysis, Ohgi et al. identified three compounds specific to the ovulatory phase: (E)-geranylacetone [floral, green], tetradecanoic acid [“oxidized sebum odor quality”] and (Z)-9-hexadecenoic acid [“nearly odorless”].

The next stage of the study involved another novel feature. Oghi et al. mixed up a synthetic blend of seven fatty acids intended to mimic the baseline odor of the female armpit. This might be the first time anyone has created an armpit aroma cocktail. [It needs a name.—Ed.] [Okay, let’s call it an Armpitini.] The team also created a mixture of the three ovulatory-phase specific compounds—a blend we’ll call Triple Spec.

Male raters assessed the Armpitini, the Triple Spec, an Armpitini spiked with Triple Spec, and a no-odor control. They rated the samples for intensity, pleasantness, and a bunch of odor descriptors (e.g., woody, sweet, sweaty, stinky). The pattern of results showed that the Triple Spec blend modulated the Armpitini aroma in a generally positive direction. For example, compared to a straight up Armpitini aroma, the Armpitini + Triple Spec was less intense, less unpleasant, less sweaty, and so on.

Ohgi et al. try to sell these results as evidence that the ovulatory phase Triple Spec compounds (E)-geranylacetone, tetradecanoic acid and (Z)-9-hexadecenoic acid have a specific, favorable impact on armpit odor during the ovulatory phase. I’m not sure I buy it. It’s more likely that these are merely instances of classic odor mixture suppression. When odor A has an intensity of 4 and odor B has an intensity of 8, the combination of A+B always has an intensity of less than 12, i.e., intensity is not additive. I think that’s what happened here.

Finally, Ohgi et al. decided to evaluate how the various female axillary odors impact men’s self-reported mood and their evaluation of photographs of female faces. Each male panelist sat alone in a test booth and wore a headset—the researchers secretly applied a test aroma to the microphone. When exposed to Armpitini aroma mixed with ovulatory Triple Spec, men’s impressions of female faces were more positive, and their self-reported hostility and stress were lower.

Ohgi et al. sum it up thusly:

We identified three ovulatory phase-increasing compounds that mitigate the basal unpleasant axillary odor, resulting in the ovulatory-phase body odor being perceived as the most pleasant by males. Additionally, these compounds alleviated hostility and stress induced by the basal axillary odor, leading to relaxation in males and an enhanced positive impression of female facial images.

That’s a fair summary of this complex study. It’s consistent with the common idea that a pleasant ovulatory-phase scent is an evolved chemosignal—a green light for males to approach and seek copulation.

But think about the implications. Using the same logic, are we to assume that the more unpleasant axillary odor of the other menstrual phases is an evolved signal for males to stay away? Does the scent of the non-ovulatory armpit say “not tonight, darling”? And has that scent also evolved to make males feel stressed and hostile?

That’s a pretty grim model of sexual communication. It sounds like the theory of pheromones according to Al Bundy.

Ohgi et al. note that “[i]n humans, several studies have suggested that female body odor signals periods of high fertility.” My question to them is: Does it signal fertility or ceasefire?

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Nozomi Ohgi, Mika Shirasu, Yusuke Ogura, Yukei Hirasawa, Masako Okamoto, Rieko Kawamura, Hirosato Takikawa, and Kazushige Touhara, Human ovulatory phase-increasing odors cause positive emotions and stress-suppressive effects in males. iScience 113087, 2025.