How Smell, Taste & Pheromone-Like Chemicals Control You
Summary
This episode explores the neuroscience of chemical sensing — how smell, taste, and body-produced chemicals fundamentally shape human biology, behavior, and hormones. Andrew Huberman breaks down the mechanics of olfaction and taste, explains pheromone-like chemical communication between humans, and provides practical protocols to enhance sensory perception, cognition, and brain health.
Key Takeaways
- Nasal breathing during focused work enhances learning and memory — inhaling through the nose increases brain arousal and alertness, while exhaling produces a measurable dip in cognitive performance.
- Practicing 10–15 deliberate sniffs before smelling or eating significantly heightens olfactory and taste sensitivity, with long-term benefits from even occasional training.
- Olfactory neurons are unique — they are the only brain neurons that continuously regenerate throughout life, replenished approximately every 3–4 weeks.
- Smell loss can indicate brain damage or disease — loss of smell is an early marker in Parkinson’s disease, COVID-19, and traumatic brain injury (TBI); recovery of smell after TBI signals neurological healing.
- Tears contain chemicals that biologically alter others — a Science study showed that smelling women’s tears reduced testosterone and sexual arousal in men, demonstrating that human chemical communication is real and measurable.
- The tongue map is a myth — taste receptors for sweet, salty, bitter, sour, umami, and possibly fat are distributed uniformly across the tongue, not in separate zones.
- Each of the five tastes serves a specific survival function — detecting energy (sweet), electrolytes (salty), toxins (bitter), amino acids (umami), and spoiled food (sour).
- Dopamine drives olfactory neuron neurogenesis — elevated dopamine (from exercise, new relationships, or certain medications) promotes the growth of new smell-detecting neurons.
- Peppermint scent increases alertness and attention through activation of olfactory-amygdala arousal circuits, similar to (but less intensely than) ammonia smelling salts.
Detailed Notes
How the Sense of Smell Works
- Volatile chemicals (airborne particles) enter the nose during inhalation and contact the olfactory mucosa — a mucus-lined tissue in the nasal cavity.
- Olfactory neurons extend small processes (dendrites) out of the skull through the cribriform plate into the nasal mucosa, where they detect odorant compounds.
- The olfactory bulb, located approximately 2 cm above the roof of the mouth, processes these signals and sends them to the brain via three distinct pathways:
Three Olfactory Pathways
- Innate threat responses — hardwired reactions (e.g., to smoke, ammonia) routed to the amygdala; trigger alertness, fear, and threat detection without prior learning.
- Innate appetitive responses — hardwired attraction to pleasant smells (e.g., food); triggers approach behavior and the “mmm” sensation; also requires no learning.
- Learned associations — formed through experience; responsible for memories evoked by smell (e.g., grandmother’s home, seasonal scents). This pathway explains why smell is so tightly linked to autobiographical memory.
Accessory Olfactory Pathway
- A separate or embedded system responsible for pheromone-like effects in other mammals (rodents, mandrills).
- In rodents, exposure to a novel male’s scent can cause spontaneous miscarriage in pregnant females (Bruce effect); exposure to a sexually mature male’s scent can trigger early puberty in females (Vandenbergh effect).
- Whether true pheromone effects exist in humans remains controversial, though chemical communication between individuals via tears, breath, and skin is well-documented.
The Sniffing-Cognition Connection
- Research from Noam Sobel’s lab (UC Berkeley / Weizmann Institute), published in Nature Human Behavior, demonstrated that the act of inhaling — independent of what is being smelled — phase-locks cognition and elevates brain arousal.
- A separate Journal of Neuroscience paper showed that restricting subjects to nasal-only breathing improved learning compared to mouth breathing.
Protocol: Sniff Training
- Before smelling or eating: perform 10–15 deliberate nasal sniffs with no particular target odor, then smell the food item or object.
- This “pre-sniffing” wakes up olfactory neurons and increases sensitivity — comparable to widening the eyes to improve visual perception.
- Effect is measurable and has long-term benefits even with occasional practice.
- Applicable for: enhancing food experience, training smell discrimination, and recovering olfactory function after injury.
Olfactory Neuron Regeneration
- Olfactory sensory neurons are unique among all brain neurons in that they turn over continuously — dying and being replaced approximately every 3–4 weeks.
- New neurons originate in the subventricular zone, migrate through the rostral migratory stream, and settle in the olfactory bulb.
- This process (neurogenesis) is enhanced by:
- Regular exercise (increases blood flow)
- Social interactions
- Repeated exposure to diverse odors
- Dopamine signaling (motivation, novelty, new relationships)
- Some antidepressants that affect the dopamine system (e.g., Wellbutrin/bupropion) have been reported to cause sudden increases in olfactory sensitivity within days.
Smell and Brain Health
- Smell loss (anosmia) is correlated with early-stage Parkinson’s disease, cognitive decline, and aging-related neuronal loss.
- Loss of smell was a prominent early symptom of COVID-19.
- In traumatic brain injury (TBI), the cribriform plate can shear olfactory neuron projections, causing smell loss. Recovery of smell is a meaningful indicator of neurological healing.
- Recommended reading: Olfactory Dysfunction in Traumatic Brain Injury: The Role of Neurogenesis — Marin et al., Current Allergy and Asthma Reports, 2020.
- Post-injury olfactory training (deliberate smelling practice) has shown promising results for TBI recovery.
Sniffing Reflex in Clinical Assessment
- The sniffing response to an odor placed below the nostrils is used clinically to assess potential for recovery from coma or brain-dead states — a preserved sniff reflex indicates residual brain function.
Smelling Salts and Alertness Chemicals
- Ammonia-based smelling salts trigger innate threat pathways (olfactory → amygdala) and produce a powerful adrenaline/epinephrine surge, increasing maximal force output in athletes.
- Reference: Acute Effects of Ammonia Inhalants on Strength and Power Performance in Trained Men, Journal of Strength and Conditioning Research, 2018.
- Caution: Direct inhalation of raw ammonia can damage the olfactory epithelium and irritate the eyes.
- Peppermint scent also increases alertness and attention via the same arousal pathways, though less intensely.
- Both act through the same general arousal system (adrenaline/epinephrine) triggered by a wide range of stimuli.
Human Chemical Communication (Pheromone-Like Effects)
- A landmark Science paper demonstrated that men who smelled women’s sadness-evoked tears (vs. saline control) showed:
- Significant reduction in testosterone
- Reduced activation in brain areas associated with sexual arousal
- Tears, sweat, breath, and skin all release chemicals that modulate other people’s hormones and nervous systems.
- Study limitations: only female tears / male subjects were tested; broader combinations not yet studied.
- These effects likely operate through close proximity — in couples, families, and friendships — even without conscious awareness.
The Five (Possibly Six) Tastes
The tongue map from textbooks (different tastes in different regions) is completely inaccurate — all taste receptors are intermixed across the tongue surface,