Essentials: How Smells Influence Our Hormones, Health & Behavior | Dr. Noam Sobel
Dr. Noam Sobel discusses the neurobiology of smell, revealing that humans have a sophisticated olfactory system with ~7 million receptors of 350 different types that influence behavior, hormones, and social bonding through chemical signals. He presents research on how body odors affect friendship formation, how tears chemically reduce testosterone, and how babies emit hexadecanal to modulate parental aggression.
Summary
Andrew Huberman interviews Dr. Noam Sobel about olfaction and chemosensory signaling in humans. Sobel explains the anatomical basis of smell: airborne molecules travel through the nose to the olfactory epithelium, where approximately 7 million receptors of about 350 different types bind to odorants and convert them into neural signals. These signals travel through the olfactory nerve to the olfactory bulb, which creates a map based on receptor activation patterns, then project to multiple brain regions including piriform cortex, amygdala, hypothalamus, and cerebellum. Sobel emphasizes that the olfactory bulb map does not persist in other brain regions, making central olfactory coding still poorly understood.
Sobel challenges the perception that humans have a poor sense of smell compared to dogs, arguing instead that humans possess an "utterly remarkable" sense of smell. He describes a handshaking study where participants unconsciously sniff their hands after shaking hands with strangers—an olfactory behavior measured through nasal airflow monitoring. He also discusses research on "click friendships," where pairs of friends who instantly bonded were found to have more similar body odors than random pairs, as measured by both electronic noses and human raters. This suggests odor similarity contributes causally to friendship formation.
Sobel explains the research on hexadecanal, an odorless molecule abundant in baby feces and breath that has opposite effects on men and women: it reduces aggression in males while increasing aggression in females. He interprets this as an evolutionary adaptation where babies emit a chemical signal that simultaneously makes fathers less aggressive and mothers more protective—both beneficial for infant survival. This demonstrates how infants engage in "chemical warfare" for self-protection.
On the topic of tears and hormones, Sobel describes research showing that emotional tears from women, though completely odorless, cause a significant 14% drop in free testosterone in men within 20-30 minutes—an effect size comparable to strong pharmacological interventions. This finding was replicated by an independent South Korean research group. Brain imaging shows tears also dampen activity in the hypothalamus and fusiform gyrus. Comparable effects were later discovered in rodents, where mouse pup tears reduce aggression in adult males through smell-dependent mechanisms.
Sobel discusses his lab's recent breakthrough in digitizing smell through algorithmic frameworks that predict perceptual similarity between molecular mixtures with high accuracy. His team created "olfactory metamers"—completely different molecular compositions that smell identical—and successfully generated a non-overlapping version of Chanel No. 5. In collaboration with an atmospheric chemist, they achieved the first odor transmission over IP, successfully recreating the smell of violets. Sobel contextualizes this as equivalent to circa-1956 black-and-white television and projects that once olfaction is digitized to 4K resolution, it will enable medical diagnostics since every disease has a characteristic metabolic odor profile.
About this episode
In this Huberman Lab Essentials episode, my guest is Dr. Noam Sobel, PhD, a Professor of Neurobiology at the Weizmann Institute of Science and an expert on the human sense of smell. We discuss how the brain processes odors and how smell shapes our lives more than we realize, influencing everything from who we become friends with to how we experience emotions, hormones and aggression. Dr. Sobel also shares his lab’s groundbreaking work on digitizing smell and future technologies that could enable noninvasive disease detection through body odors. Read the full episode show notes at hubermanlab.com. Thank you to our sponsors AG1: https://drinkag1.com/huberman Eight Sleep: https://eightsleep.com/huberman LMNT: https://drinklmnt.com/huberman Timestamps (00:00:00) Noam Sobel (00:00:20) Biology of Smell (Olfaction) (00:04:32) Human Smell, Social Interaction, Handshaking (00:08:31) Sponsor: LMNT (00:10:03) Friendship, Body Odor (00:14:04) Human Chemosignals, Smell of Fear & Contagion (00:15:48) Aggression, Chemosignals, Men vs Women, Babies (00:20:38) Sponsor: AG1 (00:21:51) Tears, “Chemical Blanket”, Testosterone (00:25:37) Digitizing Smells (00:28:25) Sponsor: Eight Sleep (00:29:48) Creating Digital Odors; Future Medical Diagnostics (00:33:43) Acknowledgments Disclaimer & Disclosures Learn more about your ad choices. Visit megaphone.fm/adchoices
Key Insights
- The human olfactory epithelium contains approximately 7 million receptors of about 350 different types, meaning a meaningful percentage of the human genome is devoted to olfactory receptor subtypes.
- Humans unconsciously sniff their hands immediately after handshaking with strangers, a behavior verified through nasal airflow monitoring, suggesting handshakes serve a covert olfactory function.
- Pairs of friends who experienced instant bonding ('click friendships') have statistically more similar body odors than random dyads, and this odor similarity appears to causally contribute to friendship formation rather than resulting from it.
- Hexadecanal, the most abundant chemical in baby feces and breath, reduces aggression in males while increasing aggression in females—functioning as an evolved mechanism where infants chemically manipulate parental behavior for protection.
- Emotional tears from women are completely odorless to human perception yet cause a 14% reduction in free testosterone in men within 20-30 minutes, an effect size rarely achieved through pharmaceutical intervention.
- The olfactory bulb creates a precise receptor-identity map that does not persist in downstream brain regions, meaning central olfactory coding mechanisms remain poorly understood by neuroscientists.
- Sobel's lab has developed an algorithmic framework that can predict the perceptual similarity of any two molecular mixtures with high accuracy and has created 'olfactory metamers'—completely different molecular compositions that smell identical to human perceivers.
- The first odor successfully transmitted over IP using algorithmic recreation of primaries was violets, representing a proof-of-concept milestone comparable to 1950s television technology rather than modern high-definition transmission.
Topics
Transcript
Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health, and performance. I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. And now for my discussion with Dr. Noam Sobel. Dr. Sobel, Noam, welcome. Thank you. I must say, I am extremely excited for this conversation. I've been a huge fan of your work. And today I'd love for you to share with us all about the amazing landscape of chemo sensation, in particular olfaction or sense of smell, and some related perceptual abilities or subconscious abilities, including pheromones, et cetera. To get everybody on the same page, I'd like…
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