Study: Men smell and that will stress you out

ferret-specific neurons

A study in Nature Methods has kicked up a bit of a fuss:

In 2007, his lab observed that mice spend less time licking a painful injection—a sign that they’re hurting—when a person is nearby, even if that “person” is a cardboard cutout of Paris Hilton. Other scientists began to wonder if their own data were biased by the same effect. “There were whisperings at meetings that this was confounding research results,” Mogil says.


Male, but not female, experimenters induce intense stress in rodents that can dampen pain responses, according to a paper published today in Nature Methods. Such reactions affect the rodents’ behaviour and potentially confound the results of animal studies, the study suggests.

Yup, the paper says that the stench of men is just plain stressful to rodents. And it’s just human males, but males from many (most?) species.

It is pretty well-established that many animals have neurons that have an innate response to the odor of other animal species. Look at the percent of neurons in the vomeronasal organ (VNO) of the mouse that detect the scent of specific other animals:

Conspecific cells


I suppose that means it shouldn’t be surprising that there would be a way to detect males across species. And the data from this paper kinda-sorta points to that: bedding from male guinea pigs, rats, cats, and dogs induced stress-related behaviors but not when the bedding came from castrated males (poor guys). Overall, the affect of the stress was stronger on the female than the male mice.

There are three interesting take-aways from this paper. First, obviously, is that males stress out mice they handle more than females do – and they stress out female mice more than male mice. Second, certain male-specific effects seem to require both an odor and the physical presence of the (male/female) handler. Third, the odor isn’t likely to be a pheromone but rather a complex mix of odors. Three of the stress-inducing odors that they identify are 300 μM (E)-3-methyl-2-hexenoic acid (3M2H), 0.75–3 mM androstenone and 0.75–3 mM androstadienone (4,16-androstadien-3-one), which I’m sure everyone is familiar with! The first is a fatty acid that contributes to “Caucasian male underarm odor” (yum), the second is a steroid found in sweat and urine (and celery), and the third is a metabolite of testosterone.

Also, let’s take a moment to pity the poor grad students who had to take “repeated rectal measurement of core [mouse] body temperature”.


Isogai Y, Si S, Pont-Lezica L, Tan T, Kapoor V, Murthy VN, & Dulac C (2011). Molecular organization of vomeronasal chemoreception. Nature, 478 (7368), 241-5 PMID: 21937988

Sorge, R., Martin, L., Isbester, K., Sotocinal, S., Rosen, S., Tuttle, A., Wieskopf, J., Acland, E., Dokova, A., Kadoura, B., Leger, P., Mapplebeck, J., McPhail, M., Delaney, A., Wigerblad, G., Schumann, A., Quinn, T., Frasnelli, J., Svensson, C., Sternberg, W., & Mogil, J. (2014). Olfactory exposure to males, including men, causes stress and related analgesia in rodents Nature Methods DOI: 10.1038/nmeth.2935


3 thoughts on “Study: Men smell and that will stress you out

    • I think any odorant released from an animal can be a pheromone so long as another detects and uses it (technically, it is a pheromone if it is within-species and a kairomone if it is across-species).

      I went back and realized I read it a bit wrong: they do claim it has to be an ‘odor’ and not a ‘pheromone’, but for a kind of weird reason. They tested three chemicals, two of which are structurally different from the third, and they all have a similar effect. They conclude it is not a ‘substance-specific pheromone-like effect’; in other words, it is not one thing causing a specific effect, but rather the collection or mix of odorants. I don’t understand why it precludes that, however; surely you could have multiple pheromones producing a similar effect?

      Anyway they want it to be the ODOR (ie mixture of odorants) that is the signal, not any individual odorant/pheromone. I don’t think the data necessarily supports that, though.

  1. Ya, I was confused about why it’s not considered a pheromone. I just read this from a book chapter abstract by Minghong Ma at Upenn and the difference is a bit more clear now…

    “General odors activate odorant and their host olfactory sensory neurons (ranging
    from narrowly- to broadly-tuned) in a combinatorial manner and the information is sent to the brain via the main olfactory system leading to perception of smells. In contrast, pheromones stimulate relatively narrowly-tuned receptors and their host vomeronasal organ neurons and the information is sent to the brain via the accessory olfactory system leading to behavioral and endocrinological changes. Recent studies indicate that the functional separation between these two systems is blurred in some cases
    and there are more subsystems serving chemosensory roles.”

    So I guess the difference lies in the kind of receptors and which pathway the information travels. I still don’t understand how they can conclude it is an odor (especially when we know so little about human pheromones). Regardless, I think it is a very important study!

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