Podcast Summary: The Rest Is Science

Episode: Why Can't You Smell The Inside Of Your Nose?
Hosts: Professor Hannah Fry & Michael Stevens (Vsauce)
Date: January 13, 2026

Overview

In this episode, mathematician Hannah Fry and YouTuber-science creator Michael Stevens explore the science of smell—including why you can't perceive the scent of your own nose. They debunk the myth that human olfaction is "inferior," unravel the complicated relationship between our brains, bodies, and the odors all around us, and reveal how our sense of smell is both more sophisticated and more limited than we realize. Through lively banter, stories from scientific history, personal anecdotes, and surprising case studies, Fry and Stevens demonstrate that the world of smell is full of hidden complexity—and suggest our experience of reality is not as complete as we think.

Key Discussion Points & Insights

The Perceived “Inferiority” of Smell

• Victorian roots of olfactory snobbery: Hannah traces the idea that smell is base or “animalistic” to 19th-century Victorian scientists, particularly Paul Broca, who noted the small size of the human olfactory bulb and claimed this marked our “transcendence” over animal senses.
  • Quote (Hannah, 05:15):
    “This is essentially Victorians being dismissive of anything they didn’t consider highfalutin... they said we've transcended the kind of animal-like senses...smell and taste, that's more about kind of dirt and lust and savages.”
• Modern understanding: Michael pushes back, highlighting research indicating that humans can distinguish between trillions of odors—arguably as impressively as many animals, just with less spatial acuity or conscious attention.
  • Quote (Michael, 07:16):
    “Humans can differentiate seemingly trillions of different smells...if you give them two smells and ask ‘are these different?’ they can tell down to tiny percent changes.”

Human Olfactory Sensitivity—and Blind Spots

• Selective sensitivity: Humans are extremely sensitive to some molecules (e.g. the ripe-banana chemical, or ethyl mercaptan added to natural gas), but still often fail to notice faint smells unless they are “slapped in the nose” by high concentrations.
  • Quote (Michael, 09:35):
    “We are really sensitive to [ethyl mercaptan]. We can detect 0.009 parts per billion...but even though we can detect small trace amounts, it doesn’t get our attention. We have to be slapped in the nose by a smell to notice it.”
• Habituation/adaptation (olfactory fatigue): Both hosts discuss how quickly humans become desensitized to constant odors, such as their own body or home, a phenomenon called “olfactory fatigue.”
  • Quote (Michael, 22:11):
    “You cannot try to smell even if you try, because you’ve adapted to it to the point at which your neurons cannot even respond to that smell anymore.”

Much of “Smelling” Is Unconscious

• Spatial limitations: Unlike sight or sound, humans have poor “coordinate systems” for smells; we can detect but struggle to “locate” odors in space, in contrast to animals like dogs.
  • Quote (Michael, 12:31):
    “When a room smells, the room smells. We don’t think, oh man, that area of the room is smelly...[but] with sight or sound, [we perceive] a source. Smells are just present.”
• Attention and active sniffing: Michael notes that animals sniff constantly and actively, while humans mostly use passive breathing, reserving conscious sniffing for rare occasions.
  • Quote (Michael, 17:48):
    "A rat especially, like, every breath they take is a sniff...We only do that every few seconds. Most of human breathing is just for the air. Then every so often, we might go take a bigger one that really gets odorants on that olfactory bulb."

Fascinating Case Studies & Experiments

1. Vultures and Gas Leaks ([10:33])

• Engineers in 1930s Texas noticed turkey vultures circling above gas pipelines. The birds were attracted to ethyl mercaptan—a compound added to gas for humans to detect leaks and also produced by decomposing flesh.
• Quote (Hannah, 11:30):
  “It turns out that ethyl mercaptan is...the smell of death that attracts vultures, but that we are deliberately putting in as this...smell signature in order to sort of save us from gas leaks.”

2. Human Olfactory Tracking ([31:26])

• A study blindfolded people and asked them to follow a chocolate scent trail across a lawn. Despite the awkwardness, participants were able to follow the smell, especially with practice.
• Quote (Hannah, 31:45):
  “They were there, sniffing, deliberately paying attention...in most cases, they were able to follow the trail. Crucially, the more they practiced, the better they got at it.”

3. The “Super Sniffer” and Parkinson’s Disease ([34:59])

• Joy Milne, a Scottish woman, could smell a distinct scent on her husband before his Parkinson’s diagnosis—and later identified undiagnosed patients based on smell alone, leading to new research on olfactory diagnostics.
• Quote (Hannah, 35:55):
  “Eight months later, that person who she had sniffed Parkinson’s on ended up being diagnosed...She’d got the full whammy, right? 12 out of 12 correct.”

4. Dirty T-shirt Study ([25:14])

• Women preferred the smell of T-shirts worn by genetically dissimilar men, supporting the idea that body odor plays a subconscious role in mate selection.

5. Deodorant and “Febreze” Stories ([27:30], [29:16])

• Most people prefer deodorants that mimic their own molecular scent.
• The story of Febreze—a product that perfectly neutralized odors—underscored that people didn't equate “no smell” with “clean”; a scent had to be added for consumer acceptance.
  • Quote (Hannah, 29:54):
    “They couldn’t smell their own home, couldn’t smell the stinkiness...it just smelled like nothing, and nothing didn’t feel clean.”

Why You Can’t Smell the Inside of Your Nose

• Adaptation and biological limits: The olfactory neurons become exhausted (“run out of vesicles”) for the constant odors within your own nose.
  • Quote (Michael, 22:11):
    “You’ve adapted to [the smell] to the point at which your neurons cannot even respond...they don’t have the letters...to write a letter to your brain.”
• You only notice it if something changes (e.g., when you have a cold), but otherwise, your nose’s baseline scent becomes invisible to you.

Notable Quotes & Memorable Moments

• On why humans underestimate their sense of smell:
  “We just don’t sniff enough. That’s humans’ problem, Hannah.” — Michael (17:48)
• On Febreze and the psychology of “clean” smells:
  “Nothing didn’t feel clean. So instead, they reformulated it, added perfume...and that was when it really took off as a product.” — Hannah (29:54)
• On super smellers and hope for disease detection:
  “She’d got the full whammy, right? Like 12 out of 12 correct...this one woman...opened out this whole new area of research of, like, electronic noses.” — Hannah (36:00)
• On blissful ignorance:
  “You wouldn’t be able to smell it, though. That’s the problem. Because I want to know what I smell like. But we live our lives with this blissful ignorance...” — Michael (37:24)
• On the “centipede’s dilemma”:
  “As soon as someone says, wait, think about what you’re doing...you go, oh, shoot. Like, I don’t know. It’s just happening.” — Michael (37:36)
• Final answer to the episode title:
  “When it comes to the question of what does the inside of your nose smell like? The answer is you’ll never know. But thank goodness you won’t.” — Hannah (38:17)

Important Timestamps

• [02:23] – Anecdotes about sensing your “house smell”; the relativity of olfactory experience
• [04:07] – Core episode question: “What else is constantly around you that also has a smell you can’t smell?”
• [05:15] – Victorian attitudes and modern research on human smell
• [08:08] – Why gas leaks need added odor (ethyl mercaptan)
• [10:33] – Vultures detecting gas pipeline leaks and the evolution of smell detection
• [12:31] – Why humans are bad at spatial mapping of smells
• [17:48] – The physiology of sniffing: why humans “don't sniff enough”
• [19:16] – “Change anosmia” and why we don’t notice most everyday odor changes
• [22:11] – Olfactory fatigue and why you can't smell your own nose
• [25:14] – Dirty T-shirt studies and scent in attraction
• [27:30] – Deodorant preferences; the surprising results of scent-mimicry studies
• [29:16] – Febreze and the importance of the scent of “clean”
• [31:26] – The human “dog” experiment: following a scent trail on all fours
• [34:59] – The Joy Milne “Super Sniffer” Parkinson’s case
• [37:36] – The centipede’s dilemma and the unconscious proficiency of our senses
• [38:17] – Closing thoughts on why you’ll never truly know what you smell like

Conclusion

Why can't you smell the inside of your own nose?
You can’t, and it’s a feature—not a bug! Through adaptation, your brain filters out your constant, personal smell for efficiency, leaving you oblivious to your own aroma but still gently attuned to changes and differences in the world around you. The conversation peels back the layers on what makes our sense of smell both underappreciated and, in some ways, surprisingly powerful—a hidden soundtrack to our lives, mostly playing in the background.