Wednesday, September 20, 2017

Anthropogenic Aroma Compounds

aka Human Body Odor
aka apocrine bromhidrosis, axillary osmidrosis
aka Is that Me [I Smell]?

Body odor network graph

Sweat doesn't smell, per se; what smells is the metabolism of skin flora. These are colonies of bacteria that live on your armpits, but can also be found around the areola, anogenital, and navel regions.

Kids don't smell the same as adults, because the bacteria haven't colonized their bodies yet. Old people, it seems, smell different because they produce a chemical referred to as, simply, "old people smell" (see below: trans-2-Nonenal).

Below are some aroma compounds produced by the human body, via either sweat or urine:

Methyl hexanoate
ethereal, pineapple

Methyl octanoate
citurs-like, fruity, green-like

Methyl nonanoate

Methyl decanoate
oily, fruity, wine-like

all methyl -noates
fatty acid esters; found in human sweat, possibly related to odor preference mate selection; some share the same chemical formula with Propyl hexanoate aka propyl caproate, ethyl heptanoate, butyl pentanoate; scent of propyl hexanoate described as blackberries, pineapple, cheese or wine

4-Hydroxybutanoic acid lactone
caramel; perhaps related to Hydroxybutyric acid (GHB) -
produced as a result of fermentation, and so is found in small quantities in some beers and wines; structurally related to the ketone body beta-hydroxybutyrate, although that is technically a carboxylic acid; perhaps related to diabetes and hangovers

lemon, lime, orange, oily, rose, apple, coconut, grape, grapefruit, melon, peach, meaty, nutty, vegetable-like, waxy; aka Nonanaldehyde, pelargonaldehyde; an alkyl aldehyde; produced by the human body and attracts mosquitos; responsible for the “smell of metal” along w decanal and the main component Oct-1-en-3-one (1-octen-3-one)

ethereal, apple; propanone; active ingredient in nail polish remover and paint thinner; normally present in blood and urine. People with diabetes produce it in larger amounts; it is the ketone produced by the body in the metabolism of fats; produced by the liver whenever the liver has to produce glucose at a very high rate, such as in diabetes

Vanillic acid
chocolate, creamy, grape, nutty, wine-like

4-hydroxy-3-methoxybenzoic acid; a dihydroxybenzoic acid derivative; oxidized form of vanillin; found in the root of Angelica sinensis, and Açaí oil Euterpe oleracea; main natural phenol in argan oil; found in wine and vinegar; main catechins metabolites found in humans after consumption of green tea infusions

Butyric acid
cheese; systematic name butanoic acid; found in milk and as a product of anaerobic fermentation (including in the colon and as body odor); fishing bait additive, component of vomit, used in stink bombs; fermentation of butyric acid is also found as a hexyl ester hexyl butyrate in the oil of Heracleum giganteum (a type of hogweed) and as the octyl ester octyl butyrate in parsnip (Pastinaca sativa)

animal-like, chocolate, honey, vanilla, musty, earthy, butter, cheese, fatty, jasmine, grape, vegetable-like, wine-like; an amine; aromatic heterocyclic organic compound; produced by bacteria as a degradation product of the amino acid tryptophan; occurs naturally in human feces and coal tar; intense fecal odor; flowery smell concentrations; natural jasmine oil contains around 2.5% of indole

Floral; 3-methylindole; belongs to the indole family; occurs naturally in feces (it is produced from tryptophan in the mammalian digestive tract) and coal tar; strong fecal odor; flowery smell in low concentrations; found in orange blossoms, jasmine, and Ziziphus mauritiana; used by U.S. military in its non-lethal weaponry

floral; shrub of genus Jasminum; chemical constituents include methyl anthranilate, indole, benzyl alcohol, linalool, and skatole

Fumaric acid
sour; found in fumitory (Fumaria officinalis), bolete mushrooms (specifically Boletus fomentarius var. pseudo-igniarius), lichen, and Iceland moss; Human skin naturally produces fumaric acid when exposed to sunlight; product of the urea cycle; provides sourness; a Trans-Butenedioic Acid

Lauric acid
fatty; systematically: dodecanoic acid; saturated fatty acid; faint odor of bay oil or soap; as a component of triglycerides, comprises about half of the fatty acid content in coconut oil, laurel oil, and in palm kernel oil; found in human breast milk (6.2% of total fat), cow's milk (2.9%), and goat's milk (3.1%)

Isovaleric acid
animal-like, cheese; a fatty acid; strong pungent cheesy or sweaty smell; major component of the cause of unpleasant foot odor, as it is produced by skin bacteria Staphylococcus epidermidis (which is also present in several strong cheese types) metabolizing leucine; volatile esters have pleasing scents; produced by the oxidation of hop resins in beer, where it is seen as a defect

Phenethyl acetate
balsamic, floral, citrus, fruity, wine-like; Part of the characteristic odor of Camembert cheese, along w biacetyl (buttery flavoring for popcorn), 3-methylbutanal, methional (degradation product of methionine), 1-octen-3-ol and 1-octen-3-one (degradation products of fats), 2-undecanone, decalactone

fatty, waxy; 4-Hydroxynonenal; a,ß-unsaturated hydroxyalkenal; found throughout animal tissues; found in Clitopilus prunulus, commonly known as the miller or the sweetbread mushroom; cucumber odor of this species has been attributed to trans-2-nonenal, which is present at a concentration of 17 µg per gram of crushed tissue; see 2-Nonenal: an unsaturated aldehyde; with human body odor alterations during aging, old-person smell, smell of old books, aged beer and buckwheat

Oleic acid, natural
fatty; a monosaturated fatty acid; occurs naturally in various animal and vegetable fats and oils; monounsaturated omega-9 fatty acid; term related to olive, predominantly composed of oleic acid; makes up 59-75% of pecan oil, 61% of canola oil, 36-67% of peanut oil, 60% of macadamia oil, 20-85% of sunflower oil (the latter in the high oleic variant), 15-20% of grape seed oil, sea buckthorn oil, and sesame oil, and 14% of poppyseed oil; constituting 37 to 56% of chicken and turkey fat and 44 to 47% of lard; most abundant fatty acid in human adipose tissue; emitted by the decaying corpses of a number of insects to signal removal of dead bodies

Trimethylamine solution
oily, fishy, meaty; tertiary amine; strong "fishy" odor in low concentrations and an ammonia-like odor at higher concentrations; Trimethylaminuria is a genetic disorder in which the body is unable to metabolize trimethylamine from food sources, Patients develop a characteristic fish odour of their sweat, urine, and breath after the consumption of choline-rich foods

medicinal; major component in pig odor, human sweat; traditionally extracted from coal tar

trans-3-Methyl-2-hexenoic acid
(TMHA) is an unsaturated short-chain fatty acid that occurs in sweat secreted by the axillary apocrine glands of Caucasians and some Asians.[1]
Hexanoic acids such as TMHA have an hircine odor. Of the fatty acids contributing to Caucasian men's axillary (underarm) odor, TMHA has the most prominent odor.

*Information taken from Sigma Aldrich Flavor and Fragrance Catalog, 2013.
**wiki-scraped description fragments are meant for contextualization/disambiguation only.
***see this chart for visualization of the body odor smell network:  fusiontables

"The Smell of Ammonia in Your Sweat"

When too much nitrogen is present in your system, your body depends on the kidneys to process the excess nitrogen. This process creates urea, which can then be expelled through your urine. However, when there is too much for the kidneys to even process, then the excess nitrogen is secreted as ammonia through your sweat. When you exercise and sweat at a greater rate than normal, enough ammonia escapes for you to actually smell it…(or when your kidneys are under stress, thus processing less, and sending more through as sweat?).

Saturday, September 16, 2017

On Allergies and Sensitization

Writing about smell will get you thing about nuisance odors and about folks who think that smells are making them sick. A lot of this has to do with allergies, and allergies can be a tricky thing. There is no threshold for the amount of a thing that will elicit a reaction, and so allergies tend to be modulated by our own minds, at least to some extent. In other words, if you’re stressed, or if you’re thinking way too much about these allergies and their allergens and the environment where they come from, you may amplify the effects, and you may start sneezing or scratching at the most miniscule of exposures.

The way allergies work in the body is pretty damn confusing. There’s different kinds of allergies, some are hardwired, we might say, and some are ‘learned’ by the body. Some allergies can be deadly, like a shellfish allergy that closes your throat. Some can be just annoying, but won’t kill you or send you to the hospital (unless your body gets so hijacked by your own histamines that you smash your head into a wall).

All this being said, when I came across this short explanation on how allergies work, and I found it to be somewhat comprehendible, I thought I should repeat it here.

Most chemicals and their metabolic products are not sufficiently large enough to be recognized by the immune system as a foreign substance and thus must first combine with an endogenous protein [something that comes from inside the body not outside, endo- vs exo-] to form an antigen (or immunogen). Such a molecule is called a hapten. The hapten-protein complex (antigen) is then capable of eliciting the formation of antibodies. Subsequent exposure to the chemical results in an antingen-antibody interaction, which provokes the typical manifestations of allergy that range in severity from minor skin disturbance to fatal anaphylactic shock.
-Essentials of Toxicology, Casarett and Doull

Got all that? The “allergic reaction” is really an antigen-antibody reaction. It is your body fighting an intruder, and you are the collateral damage.


Please take a look at another post called “The Dangers of Smell and Perfumes in the Workplace” (forthcoming), but it’s based on this article: perfume in the workplace, which is an interesting look inside the work of an HR worker who has to deal with employees complaining about their smelly coworkers, and soothing the hypersensitive worker who thinks their coworker’s perfume is making them sick (it’s not; unfortunately, it’s your own mind doing that). 

Wednesday, September 13, 2017

Olfaction and Mental Health

Image: Ship of Fools, a reference to Michel Foucault's Madness and Civilization

The following article/abstract is quoted here as an introduction to the practice of using olfaction to better understand mental health:

Grete Kjelvik , Hallvard R. Evensmoen , Veronika Brezova , Asta K. Håberg, Journal of Neurophysiology. Published 15 July 2012. Vol. 108, No. 2, 645-657 DOI: 10.1152/jn.01036.2010

Odor identification (OI) tests are increasingly used clinically as biomarkers for Alzheimer's disease and schizophrenia.

ODOR IDENTIFICATION (OI) tests examine an individual's ability to correctly name an odor. In the clinic OI tests have been shown to have high sensitivity and specificity for predicting Alzheimer's disease (AD) at an early stage. This OI deficit is considered a central phenomenon as olfactory threshold, detection, and discrimination abilities are preserved (Arnold et al. 1998; Morgan et al. 1995; Serby et al. 1991; Wilson et al. 2007, 2009). Since AD pathology is first observed in entorhinal cortex and subsequently in the hippocampus (Braak and Braak 1992), OI impairments may arise from medial temporal lobe (MTL) pathology. Indeed, the early and specific OI deficit in AD correlates with the number of tangles in entorhinal cortex and the hippocampus (Wilson et al. 2007), and left hippocampal atrophy (Murphy et al. 2003). Structural changes in the entorhinal cortex and hippocampus are also present in patients with schizophrenia (Baiano et al. 2008; Bogerts et al. 1985; Ebdrup et al. 2010; Schultz et al. 2009; Witthaus et al. 2009), another group of patients with a specific OI deficit (Atanasova et al. 2008; Moberg et al. 1997, 2006; Rupp 2010). The utility of OI tests as a clinical tool depends on a better understanding of the neuronal processes underlying OI, and how OI differs from passive smelling (PS).

This point about smelling mental illness is fantastically queried by the odor author Annick Le Guérer in Scent the Mysterious and Essential Powers of Smell (1992), where she plays with the possibility of the “odor of sanctum” reported to emanate from certain saintly corpses as a result of extensive abnormal mental states which lower, or encumber the metabolic rate, leading to incomplete combustion of aromatic materials in the body. She reciprocates by suggesting such lower metabolism as a result of sustained meditation. Regardless, it is a general understanding that psychosis brings with it an identifiable smell.

Wednesday, September 6, 2017

Avian Navigation

Pigeons were fitted with mini Ticka watch cameras in 1908 by Dr Julius Neubronner to take aerial photos.
Aug 2017, BBC
Researchers from the universities of Oxford, Barcelona and Pisa temporarily removed seabirds' sense of smell before tracking their movements. … They found the birds could navigate normally over land, but appeared to lose their bearings over the sea. … This suggests that they use a map of smells to find their way when there are no visual cues.

Is there ever such thing as an animal that doesn’t use smell to navigate? Or anything for that matter? Humans use smell to “navigate.” We find the nipple by smell. We find mates by smell. (This is one of the few things about “pheromones” that’s unequivocally evidenced – it’s not the pheromones, and besides we don’t have pheromone receptors, but we do tend to like smells from people with compatible immune systems.) I really love how Alexandra Horowitz, in her book Being A Dog, describes the dog actively mapping its environment by its smells. I like how pet detectives find your escaped cat by drizzling your own urine outside your apartment complex so they have a point of familiarity to home-in on. And how could you not love this Florida woman who bottled her own scent so she could be found later as an Alzheimer’s wanderer.

Thursday, August 31, 2017

Olfaction Meets AI

Headline reads like this:

Aug 2017, BBC

And inside:

Nigerian Oshi Agabi’s modem-sized device - dubbed Koniku Kore - could provide the brain for future robots. It is an amalgam of living neurons and silicon, with olfactory capabilities — basically sensors that can detect and recognise smells.

And an explanation:

While computers are better than humans at complex mathematical equations, there are many cognitive functions where the brain is much better: training a computer to recognise smells would require colossal amounts of computational power and energy, for example.

The prototype device shown off at TED - the pictures of which cannot yet be publicly revealed - has partially solved one of the biggest challenges of harnessing biological systems - keeping the neurons alive. "This device can live on a desk and we can keep them alive for a couple of months," Agabi told the BBC.

And what do we think about this?

As much as this story is pretty nuts (if the sentence “They can live on a desk” doesn’t make your head spin…), it’s all too common a story in the tech world. Not that it’s fake news or anything, but let’s just say it is misleading to talk about “smelling robots” in this way.

The less interesting truth is that they can only be trained to smell specific molecules, not even signatures, or combinations, of molecules. A system able to smell “anything that might come up,” and able to use that information for something important, such a system could not be trained. Well, hmmm,  we get trained to do this from birth, in fact we are already learning about our olfactory environment in utero.

So if we want AI to meet olfaction, what we need to do is keep them alive for a lifetime, and give them a body, and friends and a job. You know, just like a real person. They would need to learn from the ground up, just like a real person.

However ---

There is a point being made here by Mr. Agabi that is totally in-line with the thesis of Hidden Scents. The way we use computers today will eventually be supplanted by something else. Traditional computation will still be useful, but something else will take us beyond the capacities of today’s technology (whole lotta talk in the sci-fi sphere of quantum computing, for example).

As of now, neural networks are taking us in a new direction. Granted they were used back in the 80’s, but only recently have they become a marked change in computing technique. (I like to note here the contemporaneous link between the architecture of neural networks and how it is the same thing used to mine bitcoins – the processor is no longer the key component, it’s how many graphics cards you have all wired together.)

The olfactory bulb, the crux of the olfactory system, from an information processing point of view, is a model neural network. And the fact that it’s already connected to the limbic system – the thing that makes us move, the thing that makes our bodies work, and even our emotions – this makes it a model system for so much more.

*Anyone with more comp sci knowledge than me please feel free to correct as I am no expert and speaking in pretty broad, possibly misunderstood, terms.  

Wednesday, August 30, 2017

On Sotolon

Sotolon is also related to fenugreek, and more specifically, fenugreek urine. It can be found in the scent of roasted tobacco and cannabis. If your car smells like maple syrup, you're leaking coolant. If your cannabis-smoking pipe smells like Sotolon, you're running low on cannabis. Vermont, and Canada in general, both smell like Sotolon, but because of maple syrup, not because of a lack of mechanics or lax drug laws.

Esther Ingus-Arkell,, Oct/24/2014

William F. Wooda, Jay A. Brandes, Brian D. Foy, Christopher G. Morgan, Thierry D. Mann, Darvin A. DeShazer. Biochemical Systematics and Ecology. Volume 43, August 2012, Pages 51–53

Post Script:
Only because I mentioned celery and fenugreek (a component of curry) do I list these descriptions.
Celery note: Due to vertofix, a IFF molecule (methyl cedryl ketone) which smells like vetiver/leathery. It can therefore hide as "vetiver" and musky notes in a fragrance notes pyramid.
Curry note: Usually a combination of spices, one of which has to be cumin. It also includes coriander and sometimes "dirty" musks. See L'Autre by Diptyque.
- Taken from Perfume Shrine

Saturday, August 26, 2017

Gene Editing for Behavior Design

Illustrated by Bill Butcher for The Economist

Because ants are social creatures, an ant colony is really a superorganism, making them a valuable model for studying complex biological systems. And because of the way they reproduce, scientists can edit whole colonies in one stroke.

Although ants have 350 odor receptor genes (similar to humans), they also have this thing called a coreceptor gene that every odor gene has to go through to work. Shut that one off, and you shut down the whole system.

And what happens when ants can't smell? They stop talking to other ants, stop doing their job, and they get lost from the group. That's not it though, they also saw changes in brain anatomy, where some sensory substructures didn't grow at all.

Scientists are hoping these studies can help understand how social behavior changes the way neurological disorders like schizophrenia or depression work, and how sensory development in general change the brain.

Now, as I stretch on a heavy tangent here, I think about how there are developers on the other side of candy crush and facebook whose job it is to model your behavior and then tweak it to make you stay using the product. Game theory maybe, the science of addiction perhaps? Behavior design, according to this article (an earlier attempt termed it captology). Not sure what we're calling this, but everything from dating websites to the weather channel are using these techniques to keep us tapping into the pleasure centers of our brains and therefore coming back for more. In a distant future, I wonder if we might want to try knocking out the olfactory receptors in people in order to make them more malleable. If we take away people's sense of smell, maybe they will be more easily influenced to do what we want them to do.

Researchers use CRISPR to manipulate social behavior in ants
Aug 2017,

From two different studies:
Cell, Trible et al: "orco mutagenesis causes loss of antennal lobe glomeruli and impaired social behavior in ants." , DOI: 10.1016/j.cell.2017.07.001

Cell, Yan et al: "An engineered orco mutation produces aberrant social behavior and defective neural development in ants" , DOI: 10.1016/j.cell.2017.06.051

Post Script:
The Scientists Who Make Apps Addictive, Ian Leslie, Nov 2016, The Economist

good explanation of behavior design in computer programming/software development:

When you get to the end of an episode of “House of Cards” on Netflix, the next episode plays automatically unless you tell it to stop. Your motivation is high, because the last episode has left you eager to know what will happen and you are mentally immersed in the world of the show. The level of difficulty is reduced to zero. Actually, less than zero: it is harder to stop than to carry on. Working on the same principle, the British government now “nudges” people into enrolling into workplace pension schemes, by making it the default option rather than presenting it as a choice.

When motivation is high enough, or a task easy enough, people become responsive to triggers such as the vibration of a phone, Facebook’s red dot, the email from the fashion store featuring a time-limited offer on jumpsuits. The trigger, if it is well designed (or “hot”), finds you at exactly the moment you are most eager to take the action. The most important nine words in behaviour design, says Fogg, are, “Put hot triggers in the path of motivated people.”

Unconscious impulses are transformed into social obligations, which compel attention, which is sold for cash.

see also: Addiction by Design, by Natasha Dow Schüll, Princeton 2013

Wednesday, August 23, 2017

On Imprecision

second from the bottom, does it say fake or false?

I like to say that big data is leading us from the Information Age into the Approximation Age. More data doesn't always mean more precision, and although dirty data is a negative term today, I wonder if in some time to come, we may begin to see the value in uncertainty. In fact, regarding autonomous vehicles, this seems to be where we're already headed already.

Here's a little ditty on using imprecision in algorithm development:
“A paper he wrote as a postdoc at Microsoft Research, Escaping From Saddle Points—Online Stochastic Gradient for Tensor Decomposition, describes how a programmer can use the imprecision of a common machine learning algorithm, known as stochastic gradient descent, to his advantage.

[related to unsupervised learning]
“Hopefully we will see more growth in this field, especially interesting results such as this which find that the weaknesses associated with a certain algorithm can actually be strengths under different circumstances.”

Saturday, August 19, 2017

Local Odor Vocab

Curren's SCAQMD Urban Odor Dictionary

You’re looking at a smell network based on the work of UCLA post-grad named Jane Curren. She took all the words used in odor complaints in southern California, and found the source of those complaints. These odor sources can be anything from a hidden garbage dump to a local restaurant. The size of the blue nodes doesn’t indicate smelliness; it indicates more descriptors. Restaurants have more descriptors because they have 1. More people near them and 2. A greater diversity of things that smell. (I’m guessing this.) What this chart does show is the most common odor complaints in the middle of the cluster – we smell burnt things a lot. Also rotten eggs/sulfur/natural gas.

Below, Curren went further and found the specific chemical source of these smells, and I listed them below. Next time you smell something funny, check this list. (And the next time you’re in New Jersey, take a tour of the New Jersey Turnpike mobile museum of olfactory delights, you’ll smell firsthand many of the odors on this list!)

Curren's Urban Odor Lexicon
Descriptor                           Odorant
solvent                                 2-butanone
petroleum                          2-methyl-1-propene
pungent                               2-pentanone
sweet                                   2-pentanone
lemon                                   acetaldehyde
alcohol                                  acetaldehyde
acrid                                      acrolein
pungent                               ammonia
sweet solvent                   benzene
sweet                                   dichloromethane
decayed cabbage             ethyl mercaptan
pungent                               formaldehyde
rotten egg                           hydrogen sulfide
woody                                  m-cresol
resinous                               m-cresol
medical                                                m-cresol
woody                                  o-cresol
resinous                               o-cresol
medical                                                o-cresol
woody                                  p-cresol
resinous                               p-cresol
medical                                                p-cresol
medical                                                phenol
sweet                                   phenol
irritating                               propanal
fruity                                     propanal
empyreumatic                  pyridinec
irritating                               sulfurdioxide
aromatic                              toluenec
fishy                                      trimethylamine
pungent                               trimethylamine
sweet                                   acetone
minty                                    acetone
sweet solvent                   benzene
woody                                  cresol
resinous                               cresol
medicinal                             cresol
sour                                       dimethyl disulfide
onion                                    dimethyl disulfide
decayed cabbage             dimethyl sulfide
decayed cabbage             ethyl mercaptan
garlic                                      ethyl mercaptan
aromatic                              ethylbenzene
pungent                               formaldehyde
rotten eggs                         hydrogen sulfide
skunk                                    i-propyl mercaptan
sour                                       methyl mercaptan
garlic                                      methyl mercaptan
decayed cabbage             methyl mercaptan
skunk                                    n-butyl mercaptan
skunk                                    n-propyl mercaptan
medicinal                             phenol
sweet                                   phenol
irritating                               propanal
sweet                                   p-xylene
sharp                                     thiophene
skunk                                    thiophene
rubber                                  toluene
moth balls                           toluene
aromatic                              1,2,4-trimethylbenzene
aromatic                              1,3,5-trimethylbenzene
vinegar                                 acetic acid
sour                                       acetic acid
chemical                              acetone
sweet                                   acetone
acrid                                      acrolien
pungent                               ammonia
sweet                                   a-pinene
pine                                       a-pinene
sweet solvent                   benzene
malty                                     butanal
burnt                                     butanal
rancid                                    butyric acid
sour                                       butyric acid
perspiration                       butyric acid
fruity                                     butyl acetate
dead body                          cadaverine
disagreeable sweet        carbon disulfide
almond                                 chlorobenzene
sweet                                   chloroform
ethereal                               chloroform
pungent                               crotonaledehyde
gasoline                               decane
ethereal                               dichloromethane
sour                                       dimethyl disulfide
onion                                    dimethyl disulfide
decaying vegetation       dimethyl sulfide
aromatic                              ethylbenzene
oily                                         heptanal
musty                                   heptanal
woody                                  heptanal
fatty                                      hexanal
green                                    hexanal
rotten egg                           hydrogen sulfide
sharp                                     isopropyl benzene
aromatic                              isopropyl benzene
sharp                                     cumene
aromatic                              cumene
lemon                                   limonene
decayed cabbage             methyl mercaptan
moth balls                           naphthalene
tar                                          naphthalene
sweet                                   m-xylene
gasoline                               octane
sweet                                   o-xylene
pungent                               pentanal
sharp                                     propanal
vinegar                                 propanoic acid
sour                                       propanoic acid
sweet                                   p-xylene
solvent                                 styrene
rubber                                  styrene
sweet                                   tetrachloroethene
rubber                                  toluene
moth balls                           toluene
sweet                                   tricholoroethane
fishy                                      trimethylamine
fecal                                      valeric acid
sour                                       valeric acid
sweet                                   vinyl acetate

Suffet and Rosenfeld's Urban Odor Lexicon
*much of Curren’s work came from Suffet and Rosenfeld, so I added their leftover terms here

Descriptor                           Odorant
Coffee                                  Furfruryl Thiopropionate
earthy                                   Geosmin
musty                                   2-Methyl isoborneol
moldy                                   2,4,6-Trichloroanisole
grassy                                   Cis-3-hexen-1-ol
dead animal                       Putresine
rotten vegetable              Dimethyl Trisulfide
fishy                                      Dimethyl Amine
fishy                                      Methyl Amine
plastic                                   Methyl Methacrylate
fecal                                      Indole
manure                                  Skatole
burnt                                     Guiaicol

Primary document: Curren, J. 2012. Characterization of Odor Nuisance. UCLA.

Supporting document: Suffet, I.H., and P.E. Rosenfeld (2007). The Anatomy of Odour Wheels for Odors of Drinking Water, Wastewater, Compost and the Urban Environment, Water Science and Technology 55(5), 335-344.

Research note: The descriptor names come from the above source and supporting documents, whereas the odor causing compounds were matched against varying sources which will not be listed here; see instead the source document for those references

Monday, August 14, 2017

Place Your Bets

Mr. Avery Gilbert, sensory psychologist, author of lots of books on smell, and writer for the blog First Nerve, asks the hard questions about smells. For those who aren’t on the science side of smell, this topic might be too much. But really, it’s getting to the bottom of how smell works, and how we might be able to categorize this sense that seems to be impervious to organization. Spoiler alert – it doesn’t work, and we’ll try to explain why.

Gilbert asks, “Can we predict a molecule’s smell from its physical characteristics?” This is an important question that has lots of people wishing it were true. The problem is that we can’t seem to predict what something would smell like, given any information about its molecular properties. Sure, sulfur-things smell sulfur-y. But there is a lot more to smells than that.

There is a dream out there, that a periodic table of smells really exists, that there is a chart listing all the molecules and all their smells, and all are organized into neat rows and columns. But that’s just impossible. There are infinite molecules and infinite smells. Further, there are infinite ways to describe these already-infinite things because the language of smell, as it tries to pin-down and describe, only begets more words, not less. So at the outset, this is impossible.

But still, Science is trying, and recently (this article is from February), a huge crowdsourced effort claims to have found a pretty good means of doing this. It’s called the Dream Challenge, and it uses a bunch of parameters, or features of molecules all thrown together in a big data pile, in the hopes of returning an algorithm that can smell as good as we can, but just by looking at the molecular data. These features, “4884 physicochemical total features of 338 molecules,“ might be the chemical constituents of the molecule: hydrogen, carbon, etc.; or the family of chemicals: ketones, aldehydes; or something about their three-dimensional arrangement. All these parameters are put together, and a big computer sifts through them looking for a pattern between these features and the names people give them, in regards to their smell.

So this brings us to the next part, which is the more important part, for me at least.  What do we call these molecules and their perceptive impressions? In other words, where do the names of the perceived smells come from? Scientists for decades have been using a database of smell names and their matching molecules that comes from the 1980’s and was put together by a man named Andrew Dravnieks. The odor atlas it’s called, and it’s been used for every experiment dealing with smell. It’s pretty much the only one. For the Dream Challenge, a new odor atlas was created. And therein lies the rub, for Avery Gilbert, as well as for anyone who is the least bit suspicious of science predicated on a subjective lexicon.

The new psychophysical dataset was created like this – they gather 50 people to be the smeller/namers. This is a good number, as Mr. Gilbert says, because it cancels the perceptive variability that is bound to occur between people (because for many reasons from genetics to Freudian psychoanalytics, no two people smell the same thing). Then these people are given a bunch of odorants, molecules, and asked to describe what they smell like.

These smellers don’t get to name the odorant molecules whatever they want; they are given a list of pre-determined words, like fruity or burnt. This is the first catch. In this case, the predetermined words listed only 19 (garlic, sweet, fruit, spices, bakery, grass, flower, sour, fish, musky, wood, warm, cold, acid, decayed, urinous, sweaty, burnt, and chemical). That’s more than some other studies have tried to use, but less than the available lexicon, and still less than some other recognized lexicons, like the ones used in wine (86 descriptors) and coffee (85) and the Dravnieks odor atlas (146).* Then there’s the descriptive capacity of the words chosen. “Urinous” is pretty specific, but “cold” is not. (What the heck does “cold” smell like anyway? The opposite of “warm, ” of course!)

The reason the number of descriptors is set at 19 is not because there are only 19 ways to describe the hundreds of odorants offered. The reason is because the set of all possible descriptors has been collapsed, or organized into categories. When creating a lexicon like this, many descriptors would tend to be similar – they are near each other in odor-name-space. But this can be an illusion that is really hard to penetrate. ‘Musty’ and ‘urinous’ seem like they might go together, no? Or ‘sweet’ and ‘fruity?’ And how many other things fall under the ‘garlic’ category to actually constitute it as a category? Can you call something a category if it only has one thing in it?

Avery Gilbert explains that many of these lexicons are made for specific purposes, imposing a structure on an otherwise cacophonic mess. The wine wheel is for tasting wine, the coffee dataset for tasting coffee, etc. In this case, there was no purpose; it’s supposed to be universal. And with this total lack of context, the semantic descriptors available may not directly correlate to what the smeller really smells.

Bottom line is, if this Dream Challenge comes up with an algorithm to predict what something smells like based on its chemical properties, it will be surprising.

It’s just one of those things that seems like it can’t be done. It’s one of those things that is out of its element, like a gorilla trying to mate with an elephant and expecting a healthy offspring. A psychophysical dataset is this, a gorillaphant. Chemistry is strict, rigid, objective, distinct, and quantifiable. But words are polysemous, they mean more than one thing. And smelling as a perceptive act is too personal. There is no standardization to the way we name smells. There is no Pantone for smells. We never ever learn the names of smells in a standardized way, so how can we have a universal dataset for them?

Personally, I think the National Geographic Smell Survey is a more interesting study. This is something Avery Gilbert worked on. Because it covers people all over the world, it gets a better sense of what a smell is. Smells are hard to name because they are subjective, for one, but also because the names we give them are very culturally determined. To survey people all over the world (as in the NatGeo survey) is a good way to cross cancel the problem. Then there’s the time issue. How long does something like that last? This survey was done in 1989. That’s around when Calvin Klein came out with “unisex” perfume, and way before they sold kimchee in my non-asian neighborhood supermarket. Culture changes, both across time and space, and the words we use to describe our experiences change with it. We may never have a universal smell chart, not until we ourselves are universal. (And hopefully that never happens.)

* U.C. Davis Wine Aroma Wheel uses 86 terms to describe wine, the World Coffee Research Sensory Lexicon uses 110 terms to describe coffee and the Dravnieks odor atlas uses 146.

Journal articles referenced:

“Predicting human olfactory perception from chemical features of odor molecules,” by Andreas Keller, et al., published online February 20, 2017 in Science.

“Olfactory perception of chemically diverse molecules,” by Andreas Keller and Leslie B. Vosshall, BMC Neuroscience 17:55, 2016.

National Geographic Smell Survey. Wysocki C, Gilbert AN. Ann N Y Acad Sci. 1989;561:12-28.

Image source: link

Sunday, August 13, 2017

Ask Alexandra Horowitz

Alexandra Horowitz is a teacher of psychology, animal behavior, and canine cognition at Barnard College, Columbia University, in New York City. She is also author of Being a Dog: Following the Dog Into a World of Smell. Her book is as much about human olfactory cognition as it is about dogs, and her easily accessible narrative offers a heck of a lot of information about the sense we’re all missing.

The book was great, and I am definitely not looking the same at dogs, and their walkers, after reading it. I posted a bunch of notes here. Still, I was compelled to ask her if she might give some time to answer a few questions for the blog here, and what do you know, she found a moment on her summer break to get back to us.  

AB: 1. The thing I am perhaps most fascinated with when it comes to smell is its ability to tell us things that are otherwise invisible, and at times these things can be very personal information about people.

I have heard from a friend of mine, who is really sensitive to smells, she's an eye doctor, and she says she can tell if one of her patients are cheating on their spouses (still awaiting the details of how the heck she knows that).

Do you find it uncomfortable at times to 'learn' something about someone that you shouldn't know?

AH: I don't know that I have the olfactory acuity of your doctor friend! I have definitely startled my students by knowing who had garlic with yesterday's dinner, or -- not so uncommon -- who's just had a cigarette. I think that they feel uncomfortable with someone having that knowledge, but I don't. Now, if I had a nose with the sensitivity of dogs' noses, maybe I would be gleaning information that I'd rather not have. But one can also simply not sniff....

(I would have to playfully disagree here, as I had to remind myself recently in a somewhat uncomfortable social situation – you can close your eyes, you can put the earbuds in your ears, but you can’t not smell, unless you want to not breathe.)

2. Is there any particular source you recommend for more information on astronauts and smell?

Look at the work that NASA has done to impart flavor to foods. (Also, if you run across an astronaut, ask him! That's what I did...)

(Well I guess I should ask an astronaut because all I get is this - For astronauts, there's little gravity, and this changes the pressure in your head and your sinuses, so that it's hard to breathe through your nose, which means you can't smell - and that means your food doesn't taste like anything. But that's only for the first few days; our bodies get used to it. So why does food continue to taste different? Scientists can't say for sure. For example, it could be that the confined space of the station, crowded with all the other smells of other bodies and machines etc., make a very noisy environment for our noses, and so the food is drowned out. And bland food means more spicy flavors, more Tabasco sauce.) 

3. [This is a reference to Horowitz’ recounting of the trick where a person is asked to choose a book from a shelf, hold it and thumb through the pages, then put it back. The ‘magician’ then enters the room, and recovers the chosen book; “You just smell the books,” Feynman said.] Have you ever pulled the Feynman trick as part of an informal investigation in a public place?

No! Although now that you mention it, I will try it forthwith. I have pulled out le Nez du Vin - small bottles with odors present in wines - with many visitors, and we try to guess the smell source. It's fascinating, as inevitably there will be one person who is surprisingly good at naming the odors, while the rest of us grasp at straws.

(Besides Le Nez du Vin, there's also Le Nez du Cafe, and Le Nez du Whisky. And as I happen to be looking at the World Coffee Research Sensory Lexicon, I see that there are simple ways to make on your own samples - for a papery aroma, boil a coffee filter in water and smell the water; for a 'fermented' note, get some grass and let it ferment in a jar for two weeks. Still, it’s a lot easier to carry a bottle of essential oil in your bag than a jar of fermenting vegetables.)

4. And finally, will we ever have smelling robots?

There are lots of people who are banking on it. DoD and others have funded a lot of research on developing artificial noses -- so far without surpassing a dog nose. In fact, a lot of the fascinating detail I discovered about the airflow in a dog's nose came from a Penn State group that was looking to use that information in the design of an artificial nose.

Still, no one yet knows what combination of factors (in the nose and the brain, in anatomy and behavior) leads to macrosomatic animals being so good at smelling. We will have artificial noses, but they won't soon improve upon the many very good biological ones, I'd predict.

(Artificial noses are usually designed to detect specific odors, like explosives or drugs. So to call them artifical noses needs some explaining. It's like designing an eye that can only see bright green, and then calling it an artificial eye. Not to discredit the work of artificial noses, just disambiguation. If the program she is speaking of here is DARPA's RealNose, it has since been cancelled. There have been plenty of other attempts, and some successful, to make these "single-serving robot noses," but my favorite - remote control bomb sniffing locusts!)

And so there you have it. Smelling robots are far, far away. About as far as getting a good taylor ham egg and cheese sandwich in outer space.

Much thanks to Alexandra Horowitz for taking the time to give some food for thought, beyond the wealth of information that is already presented in her book.

For more material by Alexandra Horowitz, here’s a talk on NPR, and a video from the University of California TV.

Wednesday, August 9, 2017

Seeing Smells in HD

For the foreseeable future, one of the tastiest tidbits of olfactory science will be this – the most accurate measurement of olfactory stimulus available to science uses light. That's right, the best way to know what a smell is, is to “see” it.

Smell comes from molecules, but not the kind you can see with the naked eye. Smelly molecules are vaporous, and vapors invisible. But on a molecular level, if you pulse a molecule with light, it emits light back. And if you measure the color of that light, you can identify the molecule. This is called spectroscopy, because instead of a yardstick, we use a spectrum of colors. And this is also called irony, because we use colors to smell. And this, is the nature of olfaction, because it is the most confusing, mysterious, and nonsensical of all our senses.

Post Script
The same technological advances that are presaging quantum computation via optic modulators are refining molecular spectroscopy techniques:

Monday, August 7, 2017

Brits and Twits

Some words just sound funny, and sometimes sounds are just more important than semantics.

Booty, booby and nitwit—academics reveal funniest words
Aug 2017,

Tomas Engelthaler and Professor Thomas Hills in the Department of Psychology analysed 5000 randomly selected words, and showed them to over 800 people online - asking them to rate from one to five how humourous they found each word.

The funniest words - those which had been scored highly by the most people, and given the highest mean humour rating - were (in order):


I have a feeling the sample pool here is from England not the US. Something about 'twit'.

Post Script
Sound Symbolism and Universal Language
Limbic Signal 2017

Saturday, August 5, 2017

Odors and Urban Planning

You’re looking at a 17th century plague mask. Doctors had to wear these as they went to visit the afflicted so they would not themselves be exposed. It was thought that bad smells and disease were the same thing. They weren’t totally wrong about that. Regardless, urban planning and public health came to us by way of smell. A great book to explore this relationship is Alain Courbin’s Foul and the Fragrant, about how the smell of poorly designed sewage system of 18th century Paris led to the French Revolution.

On a similar topic, I’m reading a great article about this major smell map that came out a while ago. They mention a lot of good stuff about urban planning, and one which I am very embarrassed about, because I don’t recall ever hearing this one:

In their Discussion section, where they discuss the limitations of their study, they write about contextual factors of the layout of the city and how it affects odor detection:
“The grid layout of New York City, for example, encourages large-scale collective odor experiences as it was designed in a way to facilitate airflow using prevailing westerly winds to dissipate the disease-carrying miasmas of the late 18th century.”

(I guess Manhattanhenge was just an afterthought??)

Original Source:
Quercia, Daniele, Rossano Schifanella, Luca Maria Aiello, and Kate McLean. 2015. “Smelly Maps: The Digital Life of Urban Smellscapes.” In Proceedings of the Ninth International AAAI Conference on Web and Social Media (ICWSM 2015). Palo Alto, CA: AAAI Publications. 327-336. Accessed November 28, 2016.

Full pdf:

Image source: 17th century plague mask, from Wikimedia commons, and this place too.