How Smells Influence Our Hormones, Health & Behavior _ Dr. Noam Sobel
September 30, 2026
AI Summary
5 min readHow Smells Influence Our Hormones, Health & Behavior
The widely repeated claim that bloodhounds have a billion olfactory receptors is completely made up. Dr. Noam Sobel, professor of neurobiology at the Weizmann Institute, traced this "fact" back through textbooks to an offhand comment by a geneticist who, when asked about it, replied, "What's a bloodhound?" This story captures something central about Sobel's work: the human sense of smell has been dramatically underestimated, and many things we think we know about it are wrong.
Humans can detect odors at concentrations as low as 0.2 parts per billion. Sobel's lab calculated that if you added a single drop of the odorant estratetraenol to one Olympic-sized swimming pool and left another pool untouched, a person could smell the difference between them. That detection threshold rivals any machine.
The Architecture of Smell
Airborne molecules travel about six or seven centimeters up the nose to the olfactory epithelium, where roughly seven million receptors of about 350 different types line a convoluted surface. All receptors of the same subtype converge to two specific locations on the olfactory bulb called glomeruli. This creates a map: when you smell coffee, the glomeruli corresponding to receptors that respond to coffee's molecular components light up in a characteristic pattern.
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What you'll learn
- 1 (01:51) **Introduction and Episode Overview** - Andrew Huberman introduces Dr. Noam Sobel and previews the episode's major themes: human olfaction rivaling dogs, subconscious chemical communication between people, the impact of tears on hormones, and the nasal cycle's link to the nervous system.
- 2 (10:07) **The Olfactory System: Anatomy and Basic Mechanisms** - Dr. Sobel explains the core components of the human sense of smell, from airborne molecules to brain processing.
- 3 (20:00) **Olfactory Loss, Trauma, and Recovery** - Discussion on the causes of smell loss, including head trauma and COVID-19, and the evidence for recovery methods.
- 4 (28:00) **The Nasal Cycle and Autonomic Nervous System** - Dr. Sobel describes the nasal cycle, its link to the sympathetic/parasympathetic balance, and its potential as a diagnostic marker.
- 5 (36:29) **Inhalation, Exhalation, and Cognitive Processing** - The "sniffing brain" theory suggests that nasal inhalation itself times and modulates cognitive processing, even for non-olfactory tasks.
- 6 (41:40) **Human Scent Tracking and Training** - Humans have a remarkable innate ability to follow scent trails, which can be rapidly trained to near-perfect performance.
- 7 (46:50) **The Nasal Cycle and Autonomic Nervous System (Continued)** - The discussion continues on the nasal cycle's potential as a diagnostic tool and its link to autonomic function.
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Show Notes
How Smells Influence Our Hormones, Health & Behavior _ Dr. Noam Sobel