Sniffing a molecule emitted from baby heads makes men less aggressive yet women more aggressive.

Terrestrial mammals use pheromones to effectively trigger or block conspecific aggression. Here we tested whether hexadecanal (HEX), a human body-volatile implicated as a mammalian-wide social odor, impacts human aggression. Using validated behavioral paradigms, we observed a remarkable dissociation: sniffing HEX blocked aggression in men, but triggered aggression in women. Next, using functional brain imaging, we uncovered a pattern of brain activity mirroring behaviour: In both men and women, HEX increased activity in the left angular gyrus, an area implicated in perception of social cues. Hex then modulated functional connectivity between the angular gyrus and a brain network implicated in social appraisal (temporal pole) and aggressive execution (amygdala and orbitofrontal cortex) in a sex-dependent manner consistent with behaviour: increasing connectivity in men, but decreasing connectivity in women. These findings implicate HEX as a human pheromone, whose sex-specific brain processing is at the mechanistic heart of human aggressive behavior.

Summary Plants produce myriad aroma compounds—odorous molecules that are key factors in countless aspects of the plant's life cycle, including pollinator attraction and communication within and between plants. For humans, aroma compounds convey accurate information on food type, and are vital for assessing the environment. The phenylpropanoid pathway is the origin of notable aroma compounds, such as raspberry ketone and vanillin. In the last decade, great strides have been made in elucidating this pathway with the identification of numerous aroma‐related biosynthetic enzymes and factors regulating metabolic shunts. These scientific achievements, together with public acknowledgment of aroma compounds' medicinal benefits and growing consumer demand for natural products, are driving the development of novel biological sources for wide‐scale, eco‐friendly, and inexpensive production. Microbes and plants that are readily amenable to metabolic engineering are garnering attention as suitable platforms for achieving this goal. In this review, we discuss the importance of aroma compounds from the perspectives of humans, pollinators and plant–plant interactions. Focusing on vanillin and raspberry ketone, which are of high interest to the industry, we present key knowledge on the biosynthesis and regulation of phenylalanine‐derived aroma compounds, describe advances in the adoption of microbes and plants as platforms for their production, and propose routes for improvement.

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