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Mental Health
4 Min Read
Last Updated: 12.06.23

Dr. Noam Sobel: How Smells Influence Our Hormones, Health & Behavior

Huberman interviews Noam Sobel, PhD, on the biology of smell and its effects on behavior, cognition, social connections, and hormones. They explore olfaction’s role in social sensing, emotions, memories, and disease diagnosis. Dr. Sobel shares insights on digitizing smell for online communication and its impact on human biology and behavior.

Key Takeaways

High level takeaways from the episode.

Chemosensation: ability to respond to chemicals in the environment

  • Humans are incredibly good at sensing the chemical world around them

We process information about other people’s chemicals (stress levels, hormone levels, etc.) subconsciously, impacting our emotions, decision making, and relationships.

Smelling through the nose (orthonasal olfaction) and mouth (retronasal olfaction)

  • Retronasal olfaction: odorants come up through the back of the throat and out of the nose the reverse way, contributing to food and taste

Airborne molecules travel up the nose and interact with about 6–7 million receptors in the olfactory epithelium

  • Bloodhounds have a billion receptors in their nose, making them excellent at tracking scents

Humans have a remarkable sense of smell: detection threshold for estratetraenol (odorant used in lab) is 10^-12 molar in the liquid phase

  • Equivalent to detecting one drop in two Olympic-​​sized swimming pools

Humans can improve their sense of smell: study showed humans were able to track odors in grass effectively (like a dog), and improved with training.

Nasal cycle: alternating high and low flow between nostrils every 2.5 hours on average

  • Linked to balance in autonomic nervous system (sympathetic and parasympathetic)

Nasal cycle overlooked in neuroscience, could be used as a marker for various diseases.

Nasal Halter: Wearable Device for Measuring Nasal Airflow

  • Measures airflow in each nostril separately and logs data for 24 hours
  • Can be used as a disease marker, e.g., distinguishing between ADHD and non-​​ADHD adults

Loss of sense of smell is an early sign of neurodegenerative diseases (e.g. Parkinson’s).

Standard clinical tests of olfaction:

  • UPSIT (University of Pennsylvania Smell Identification Test) — scratch and sniff test
  • Sniffing Sticks — European version, pens with odors

Congenital anosmia: being without the sense of smell from birth, affects 0.5% of the population

  • Reduced social contacts
  • Reduced romantic social contacts
  • Shorter lifespan (according to Ilona Croix’s research in Germany)

Olfaction and reproduction are tightly linked in all mammals, including humans.

Humans subconsciously identify people by their smell

  • Most of this processing is subconscious and not well understood

Study by Dan Frooming’s lab observed significant increase in subjects touching their face and nose after handshaking

  • Suggests that humans may subconsciously use handshaking as a way to gather olfactory information about others

Study: clique friends had more similar body odors than random pairs.

Reproduction and romanticism not always the same

  • Mammalian reproductive behavior dominated by sense of smell

Bruce Effect:

  • Pregnant mice exposed to the odor of a non-​​stud male (not the father) will miscarry the pregnancy
  • Occurs in about 80% of exposures

Study on couples experiencing unexplained repeated pregnancy loss; hypothesis: possible Bruce effect-​​like phenomenon in humans

  • Women with repeated pregnancy loss could identify their spouse’s body odor with much greater accuracy than control women
  • No difference in detecting other odors
  • Currently seeking ethical approval for a causal experiment

Humans emit chemosignals that influence each other’s physiology and behavior

  • The term “pheromone” is problematic and mostly used for insect behavior

Humans emit a specific body odor when in a state of fear

  • This odor increases autonomic arousal and sympathetic state in others
  • Fear can be considered contagious through the smell of fear

Mourning period post-​​breakup may involve olfactory unlearning.


  • A molecule studied in mice as a chemosignal that promotes social buffering
  • Study on humans: hexadecanal reduced aggression in men, increased aggression in women

Hexadecanal’s effects make sense for mammalian offspring

  • Paternal aggression is often directed at offspring, while maternal aggression is often protective
  • A molecule that makes mothers more aggressive and fathers less aggressive is beneficial for offspring

Hexadecanal is the most abundant semi-​​volatile in baby heads

  • Babies are reducing aggression in fathers/​​male figures and increasing aggression in mothers/​​female figures, which is beneficial for their survival

Research on human social chemo signaling focuses on the smell of fear and sweat

  • Goal is to find fear molecules and develop potential treatments for anxiety

Study: emotional tears collected from participants while watching sad movie scenes

  • Tears were odorless, but when sniffed by men, resulted in a 14% drop in free testosterone within 20–30 minutes

Dogs emit emotional tears when they reunite with their owners, influencing oxytocin in human.

Oxytocin may play a role in the strong attachment humans have to their dogs

  • Dogs may hijack the circuitry intended for child rearing through oxytocin

Studies show humans are actually very similar in olfactory perception

  • Correlation in pleasantness estimates across humans is about 0.8

Google and other companies working on digitizing smell

  • Potential applications: search engines providing smells, richer sensory experiences, influencing decision-making

First odor ever transmitted over IP was violets

  • Current device used for measuring is large and expensive ($1.5 million), but prediction is that size and cost will decrease over time


We recommend using this distillation as a supplemental resource to the source material.

  • Dr. Noam Sobel: How Smells Influence Our Hormones, Health & Behavior

    Huberman Lab #128

    Huberman interviews Noam Sobel, PhD, on the biology of smell, its impact on behavior, cognition, and social connections, and olfaction-​​based disease diagnosis.

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