What is a pheromone?

Pheromones are substances secreted by a variety of mammalian species, including humans, that mediate communication between members of the same species. It is a form of chemically-based communication with evolutionary roots. Minute amounts of that substance are sufficient to produce an immediate reaction, the nature of which varies. For example, rats produce a specific odor (i.e., pheromone) when they are stressed, which in turn elicits fear in other rats. That particular type of pheromone is also secreted in humans where it has shown to increase anxiety levels.

A pheromone that triggers anxiety

Particularly, the current study identified 4-methylpentanal and hexanal as the two molecules responsible for the anxiogenic effects of the pheromone secreted by stressed rats, which when smelled by other rates elicits behavioral avoidance, effectively warning other rats of a possible danger. The particular reaction elicited by that odor has led to coinage of the term “alarm pheromone”.

Interestingly, the characteristics of stress-related odors are similar between rats and humans, which could suggest that a similar pheromone exist in humans as well. Thence, we cannot help but wonder if, like rats, perhaps we can also smell anxiety.


Inagaki H, Kiyokawa Y, Tamogami S, Watanabe H, Takeuchi Y, Mori Y. Identification of a pheromone that increases anxiety in rats. Proc Natl Acad Sci U S A. 2014 Dec 30;111(52):18751-6. doi: 10.1073/pnas.1414710112. Epub 2014 Dec 15. PMID: 25512532; PMCID: PMC4284601

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