Sense of smell

Introduction

Definition of smell as vibratory phenomenon

Smell functions primarily as a vibratory phenomenon (not merely a shape-based “lock-and-key” mechanism) that unconsciously governs behavior, physiology, attraction, memory, health, and higher perception; ancient traditions regarded it as a supreme “judge” of consciousness, while modern factors (endocrine disruption, low CO₂, poor digestion) degrade its acuity.

Ancient philosophical significance (Heraclitus)

Historical/philosophical elevation of smell:

• Heraclitus (Fragment 37): “If everything were turned to smoke, the nose would be the seat of judgment.”
• Heraclitus (Fragment 38): “Thus in the abysmal dark the soul is known by scent.”
• Isaiah 11:3: “And by smelling in awe of the Lord… and not with his eyes see will judge, and not by what his ears hear will he decide.”

Why modern life neglects smell

Smell is rarely discussed today because modern life reduces reliance on it, yet it remains essential: “To not want to smell is to stop breathing”, it shapes taste (as a downstream sense), perfumery, and pheromone-driven sexual attraction; linguistic descriptions rely on metaphors because smells resist direct naming.

Theory of Olfaction

Vibratory theory vs. lock-and-key model

"People studying the moths have argued that it isn't possible that you could detect a gradient of a mate a mile away, and the number of molecules diffusing over such a huge space is just beyond a possible random chance. And so they have studied, usually in the infrared radiation frequency, and the vibration of a molecule, every time that the atoms oscillate farther away and closer to each other, sort of a bouncing effect within the molecule, each movement emits in the infrared frequency. And they show that the moths are detecting infrared radiation emitted by these distant molecules, so that the molecule doesn't really have to contact the animal. It's emitting a field that the animal detects." - Ray Peat

• Molecules of different shapes but identical vibrational frequencies produce the identical smell (Luca Turin’s central demonstration; see 1996 work and lecture).
• Classic example: coumarin’s sweet hay-tobacco scent replicated by synthetics matching vibration, not shape.
• Moth pheromone detection (single molecules across miles) occurs via infrared vibrational fields - incompatible with pure lock-and-key model.

Luca Turin's quantum theory

The vibratory theory of smell was revived and expanded by Dr. Luca Turin in 1996. His theory proposes that different smells are perceived based on molecular vibration frequencies rather than molecular shape alone.

The key evidence: isotope discrimination. A molecule like acetophenone and its deuterated version (where some hydrogen atoms are replaced by heavier deuterium) have identical shapes but different masses, and thus different vibration frequencies. Turin's theory predicts they should smell different, and experiments confirm this:

"The plain and deuterated versions have identical structures, but different molecular mass and as such different vibration frequencies. The TT postulates that vibrational patterns/frequencies, instead of plain molecular structure, are the true determinants of how a specific molecule would smell."

Fruit fly studies demonstrated that insects can distinguish between regular and deuterated versions of acetophenone, preferring the ordinary version, suggesting they detect vibrations characteristic of carbon-deuterium bonds.

Turin's mechanism involves quantum tunneling: electrons pass across a receptor only when bound to a molecule vibrating at the right frequency. As Turin put it, his theory "was described as impossible physically, implausible biologically" by mainstream scientists, which may itself be evidence of its correctness.

The topic of smell has come up in numerous interviews with Ray. His typical response is that the mechanism of smell is not well-known but he thinks the theories of Dr. Luca Turin are a much better explanation than the reductionist key-lock receptor mechanism mainstream medicine uses to explain smell as well as every other biological concept or drug effect.

Infrared detection by moths

The most dramatic evidence for vibratory olfaction comes from moth pheromone detection. Ray Peat explains:

"People studying the moths have argued that it isn't possible that you could detect a gradient of a mate a mile away, and the number of molecules diffusing over such a huge space is just beyond a possible random chance. And so they have studied, usually in the infrared radiation frequency, and the vibration of a molecule, every time that the atoms oscillate farther away and closer to each other, sort of a bouncing effect within the molecule, each movement emits in the infrared frequency. And they show that the moths are detecting infrared radiation emitted by these distant molecules, so that the molecule doesn't really have to contact the animal. It's emitting a field that the animal detects." - Ray Peat

This means moths detect infrared fields emitted by vibrating pheromone molecules across vast distances, a feat incompatible with the lock-and-key model, which requires direct molecular contact.

Smell and Consciousness

Connection to higher brain functions

Ray connects olfaction directly to our highest cognitive functions:

"The olfactory system is very closely connected with our highest and best conceptual work." - Ray Peat

He elaborates that smell, along with vision, is among "the very powerful things" that stimulate the brain. The conscious engagement with odors activates the higher cortical regions:

"The whole process of becoming conscious of odors in your environment, that's very closely connected with the higher parts of the brain. And conceptually, you can use odors to stimulate memory." Ray Peat

Neurogenesis in the olfactory bulb

Neurogenesis can take place in the hippocampus, but also in the olfactory bulb. Ray explains this connection when asked if smelling things can create new neurons:

"The olfactory system is very closely connected with our highest and best conceptual work."

When asked if smelling things can create new neurons, Ray affirmed that engaging with smells stimulates this process. He notes that any conscious stimulation helps:

"Nerve cells are maintaining each other so that anything you do consciously is tending to enliven the rest of your brain. It just happens that vision and smell are among the very powerful things."

Smell and memory

The connection between smell and memory is ancient knowledge. Ray invokes Heraclitus:

"Heraclitus was the person I mentioned, the Greek philosopher. Simply, so many people have noticed that an odor can recall a whole situation that you thought you had forgotten."

The mechanism works bidirectionally:

"The way they connect to the rest of the brain, you can sometimes, with a thought, you can associate the memory of a smell, and sometimes the smell can bring back certain types of thought."

Pheromones and sexual attraction

"A moth can detect a potential mate a mile away... Animals communicate very powerfully. They can detect something like one molecule per several cubic centimeters, a dilution that you can't detect with any sort of instrument" - Ray Peat

• Smelling fear via pheromones/sweat is as potent as visual or auditory cues (De Groot JH, Semin GR, Smeets MA, 2014, J Exp Psychol Gen).
• Exposure to androstenone increases women’s alcohol consumption (Tan R, Goldman MS, 2017, Exp Clin Psychopharmacol).
• Olfactory hostility signals are relayed unconsciously; temporal-lobe stimulation in mystics produces “floral” scents (Persinger).

Testosterone derivatives and male phermones

"In the case of the attractiveness of men to women, there's a definite derivative of testosterone which is very volatile, tends to come out through the skin constantly. The amount of that, people have experimented with it, taking, just extracting it right from the surface of the skin or synthesizing the same chemical and putting a tiny amount, just a milligram or so, like a mask. Putting on the women as they're evaluating, just pictures of a man, for example. And they'll say the man is beautiful and intelligent and kind and so on, if they have that pheromone present."

"The most clearly defined human pheromones are derivatives of androgenic steroids."

Progesterone and the female "aroma"

Ray's earliest olfactory memory :

"I got interested in that when I was about 11 months old. I had a 15 year old babysitter and I remember standing on her thigh and my nose had just reached her cheek and I remember the intoxicating smell of this young, healthy woman as better than any flower perfume."

The hormonal basis of female attractiveness involves progesterone:

"The progesterone level following ovulation, it's the source of much of that aroma."

Birth control and mate selection disruption

Birth control pills eliminate the natural hormonal cycle that produces attractive pheromones:

"To a great extent it does [stop the attractiveness]. The progesterone level following ovulation, it's the source of much of that aroma. Oh, so when you're ovulating, then you get the progesterone and that might attract the guys. Right? But if she's on the pill... Yeah, there's no cycle."

This has profound implications for mate selection. Women on the pill may choose partners they wouldn't otherwise find attractive:

"There's been stories... that some women marry guys because they're on the pill the whole time. And so they marry them because of whatever reason, and then they get off the pill to get a baby, and then they don't like the smell of the guy because they picked the wrong guy. I think it's very logical, biologically." [[[Ray Peat]], Patrick Timpone interview, September 21, 2021]

Birth control also affects a woman's ability to smell men properly:

"Could that affect her ability to smell the guys if she's on the pill? I think it does." [[[Ray Peat]], Patrick Timpone interview, September 21, 2021]

https://pmc.ncbi.nlm.nih.gov/articles/PMC2605820/

4.5 Children's "anti-sexual" pheromones

Ray proposes that children emit protective pheromones:

"I think little kids emit anti-sexual pheromones that I think they induce parental attitudes towards them. And then around puberty, the chemistry changes towards sexual attraction." [[[Ray Peat]], Danny Roddy podcast #70]

Smell and metabolic health

Thyroid function and olfaction

• Exaltolide (musky pheromone-like scent) is detectable only by women in the follicular/estrogen-dominant phase; men detect it only when estrogen-supplemented.
• Hypothyroidism impairs smell; thyroid hormone replacement restores it (McConnell RJ et al., 1975, The American Journal of Medicine).
• Small-intestinal irritation raises serotonin, lowers CO₂, triggers mouth-breathing and nasal blockage.

Zinc deficiency

Zinc deficiency is closely associated with smell and taste dysfunction. Research shows that people with smell and taste problems had a 30% deficit in whole body zinc.

Plasma zinc is the key marker, declining dramatically (up to 65%) even when whole body zinc only drops 5%. This is why smell/taste disturbance can appear early in zinc deficiency.

Serotonin excess

specific research on serotonin's effects on olfaction?

CO2 and nasal function

how adequate CO2 levels support nasal function

Body odor as health indicator

"Alexander the Great who apparently had great vitality in general, he was famous. Historians wrote about how sweet he smelled. People would collect his used garments because they had a permanent perfume infused into them."

"In a healthy person, the skin under the influence of thyroid hormone and feedback from the progesterone which is produced in the skin from the cholesterol, insulin and thyroid hormone are very important for keeping the flow going from energy through cholesterol into the steroids. And then those steroids include among some of the minor androgens, the pheromones, the sex attracting steroids both in men and women."

• “Old-people smell” is caused by rising skin levels of 2-nonenal (oxidative byproduct of unsaturated fatty acids) with age (Haze S et al., 2001, Journal of Investigative Dermatology).
• SSRIs and poor digestion alter body odor; restoring digestion/CO₂ levels can revive youthful pheromone perception and pair-bonding scents.
• Modern fragrance and sterilization industries mask these biological signals.

Smell unconsciously modulates desires, memory, time perception, and even spiritual awareness; its decline (aging, illness, endocrine disruption) is reversible with metabolic restoration, positioning olfaction as a “magistrate of love and health.”

Healthy vs. stressed metabolism

Body odor reflects metabolic state. Ray Peat explains:

"In a healthy person, the skin under the influence of thyroid hormone and feedback from the progesterone which is produced in the skin from the cholesterol, insulin and thyroid hormone are very important for keeping the flow going from energy through cholesterol into the steroids. And then those steroids include among some of the minor androgens, the pheromones, the sex attracting steroids both in men and women." [[[Ray Peat]], KMUD interview, November 16, 2018]

"Young fragrance" and steroid production

The "fragrance of youth" is linked to the isoprenoid pathway that produces steroids:

"I suspect that even body odor will be affected by it because it's known that some of these perfumy chemicals made by that pathway are involved in the fragrance of a young person's skin oils. And so I imagine it would tend to make a person lose their young fragrance." [[[Ray Peat]], KMUD interview, November 16, 2018]

Historical example:

"Alexander the Great who apparently had great vitality in general, he was famous. Historians wrote about how sweet he smelled. People would collect his used garments because they had a permanent perfume infused into them." [[[Ray Peat]], KMUD interview, November 16, 2018]

"Death breath" and hypoglycemia

"When you get hungry, if your liver isn't efficient, things in your tissues will come out in your exhaled breath... that smell can precede, for example, an epileptic seizure or just other, like a migraine, headache, anything where the blood sugar is inadequate and the stress hormones break down tissues."

Hypoglycemia causes a characteristic odor from stress hormone-induced tissue breakdown:

"When the liver is failing, the fats that should be breaking down and excreting can come out in the breath... But chronically they accumulate and come out more gradually in the oils." [[[Ray Peat]], KMUD interview, November 16, 2018]

This can even be observed in children:

"We call this death breath and you find it on children too... if we don't constantly feed her then the day before or the evening before, she'll wake up in the morning and she'll have this smell on her that's obviously the process by which you've described and she doesn't have it when we're really conscious about making sure she gets plenty of sugars." [Andrew Murray, KMUD interview, November 16, 2018]

"That smell can precede, for example, an epileptic seizure or just other, like a migraine, headache, anything where the blood sugar is inadequate and the stress hormones break down tissues." [[[Ray Peat]], KMUD interview, November 16, 2018]

Endotoxin and illness odor Research confirms that endotoxin (LPS) alters body odor in ways humans can detect, even subliminally:

"Elevated endotoxin/LPS alone is enough to trigger a change in body odor, which even humans (with olfactory sensitivity much worse than canines) can reliably detect, rating it as very unpleasant/disgusting, and leading to the social avoidance (isolation) of such people." [Haidut, "Illness (Endotoxin) Makes Body Odor Unpleasant, May Lead to Social Shunning"]

The changes are qualitative, not quantitative, meaning the types of volatile compounds change, not just their amounts. [Haidut, "Illness (Endotoxin) Makes Body Odor Unpleasant"]

Aging and 2-nonenal

"old person smell" compound

Phantom smells (phantosmia)

Fat-stored odors released during hypoglycemia

• Odor molecules accumulate in adipose tissue and are released into blood during hypoglycemia or fat mobilization, causing internal “phantom” smells (Mattes RD et al., 1990, The American Journal of Clinical Nutrition).

Chemicals stored in fat tissue can be released during stress-induced lipolysis. Ray explains this mechanism:

"When you get hungry, if your liver isn't efficient, things in your tissues will come out in your exhaled breath but chronically they accumulate and come out more gradually in the oils." [[[Ray Peat]], KMUD interview, November 16, 2018]

The polyunsaturated fats stored in tissues are particularly problematic because stress preferentially releases them:

"Over the years, stress is more likely to release the polyunsaturated fats." [[[Ray Peat]], KMUD interview, March 21, 2014]

This explains phantom smells: chemicals absorbed years ago (perfumes, solvents, environmental toxins) can be released during hypoglycemia or stress, causing the perception of odors not present in the environment.

Anecdotal evidence

Anecdote (Ray, 1970s Mexico): inhaled Pine-Sol-type insecticide stored in fat; smelled internally whenever blood sugar dropped and fat was mobilized.

Modern factors degrading smell

Mouth-breathing

Impairs olfactory function and overall health:

"If you don't breathe through your nose, your lungs are not meant to filter your air. There's nothing about our lungs that are designed to filter the air. So, what happens is it can take 65 days for your lungs to filter the air that your nose does in 15 minutes. And then you don't get any nitric oxide." [Heather Paul, dental health interview]

Nasal breathing produces nitric oxide, which has antimicrobial effects and supports proper olfactory function. [Heather Paul, dental health interview]

Perfume/sterilization masking biological signals

"Elevated serotonin may have some direct neurotoxic effect that may contribute to the loss of smell and taste... it's a very common side effect for people taking SSRI drugs to lose a significant portion of their sense of smell or taste. So it seems serotonin does have that direct effect."

Restoring olfactory function

Metabolic restoration

Improving overall metabolic rate is fundamental to restoring olfactory function.

"Good diet and hormone activity is the best thing to optimize the pheromones." [[[Ray Peat]], Danny Roddy podcast #70]

This includes ensuring adequate glucose availability (preventing hypoglycemic stress), supporting thyroid function, and maintaining proper progesterone levels in women.

Anti-serotonin approaches

cyproheptadine, aspirin,

See also

Luca Turin

Serotonin

Progesterone