Eau De Coli

Source.

I should begin by pointing out that I am not a perfumer. Actually I should begin by pointing out that there is such a thing as bacteria art, also called agar art, as seen above. Let me start again – I am not a perfumer; I am a writer interested in the language of smells. Obviously, perfume is a big part of that. But when I learn that bacteria are used to make perfumes it comes as a surprise to me, and I feel like I missed something. (And when I had been an art teacher for over ten years and I realize there’s such a thing as bacteria art, I also feel like I missed something, except for the fact that I only discovered radiation art a month ago.)

Apparently, fragrance experts are also a bit surprised. Engineering microorganisms to make specific odorous chemicals are a new addition to the typical methods of expression, steam distillation, and solvent extraction.

 It all started with a project done by a scientist named Reshma Shetty and a team at MIT. I'm almost as excited about the name as I am the project - it was called Eau De Coli, after the dignified Escherichia coli.  And it can be translated as "water of the colon."

E. coli isn't just for making you sick, or for making Chipotle go Chapter 11, it's also for scientists trying to research bacteria. E. coli is the model organism for scientific study, probably because of the compendium of literature already amassed due to its dangerous nature, and maybe just because it's easy to work with.

Regardless, dissertation-defending Shetty and her group engineered this archetypal organism to be a smell-generating machine. Usually E. coli smells like crap, literally, so they first had to find a mutant strain that had no genetic propensity for producing that smell. (This smell comes from the molecule Indole, by the way, and is related to Skatole, which doesn't sound like "skat" by accident.)

The next part was right out of a science fiction novel. They found enzymes that would produce the smells of wintergreen (methyl salicylate) and banana (isoamyl acetate), and they programmed the bacteria to produce those chemicals. So now, instead of smelling like crap, they smell like mint and bananas!

This is called odor engineering - a kind of genetic engineering that is used to make odor chemicals from bacteria. The researcher here, Dr. Shetty, suggests using this technique to probe bacteria at an industrial scale. Imagine you engineer the bacteria in your business to produce different smells at different stages in its metabolism. You could then tell what the bacteria are doing just by sniffing them.

Then there's others who are simply coaxing bacteria to produce otherwise difficult fragrance chemicals. Folks at the Joint BioEnergy Institute at Lawrence Berkeley Labs were originally trying to get bacteria to make biofuels. But after they accidentally discovered a way to make methyl ketones, the fragrance industry perked up.

Combining genetic-metabolic engineering and fragrance production may be a breakthrough for the industry. Now if only we could find a way to engineer ourselves not to secrete isovaleric acid from the soles of our feet!

Notes:

Dr. Shetty's genetic odor engineering Eau de Coli project:

Shetty, R. P. Applying Engineering Principles to the Design and Construction of Transcriptional Devices. Department of Biological Engineering, MIT (2008).

http://hdl.handle.net/1721.1/41843

Lawrence Berkeley Labs bioengineering efforts:

From Petri Dish to Perfume, Berkeley Science Review

http://berkeleysciencereview.com/article/from-petri-dish-to-perfume/

Post Script:

While I research odor engineering, I find some things that fall well outside the realm of fragrance.

Odor Science & Engineering, Inc. will research environments that stink and develop products that don't. Instead of using bacteria, they rely on good ol' nose megaphones (see below, a screenshot from their site.)

Source.

Here's some of the odor-absent products they have helped to develop:

High performance athletic wear

Socks

Hunting clothing

Cat litter

Trash bags

Room deodorizers

Shoe/Sneaker deodorizers

Post Post Script

Just when you let your guard down, the internet provides you with Bacteria Art, aka Agar Art. Yup.

Bacteria Art

Bacteria Art

Bacteria Art

Check out this entire gallery of bacteria art.

Roses Really Do

OutKast – Roses – 2003

video link

It’s true. Roses really do smell like the end product of our metabolism. Two major constituents of the smell of roses are Skatole and Indole, which are good olfactory representatives of excrement. They’re also used extensively in perfume.

This may or may not explain why many air fresheners (at least as far as I know since the dawn of aerosolized air fresheners) smell like roses. Regardless of whether shit and flowers go together like peanut butter and jelly, it was used a lot as an air freshener scent, at least as far as the early 90’s. (Anyone like to weigh-in here on the history of air fresheners?)

But this fact does explain why I, among others I’m sure, hallucinate excrement when smelling roses – you expect it to be there. This is called redintegration, a kind of hallucination, and it’s explained in this clip from Hidden Scents:

Part of a smell can carry with it the co-occurring odor molecules around them in the memory, and it will later be used to substitute for the whole. Strains of cannabis, aside from the strong skunk-like smell, can have significant amounts of limonene in them. Through redintegration, the potent smells of such cannabis become so tied together that upon smelling an orange (almost entirely limonene), a frequent user might hallucinate the other odors of cannabis along with the orange. This phenomenon represents an apparition superimposed in order to satisfy the nose-brains’ insistence on predicting an odor based on limited or partial information – a behavior that is not limited to olfactory perception.

Post Script

The scent of “musk” comes from the neither region of the musk deer. Just saying. Today you wouldn’t know that, because that scent of musk is now more associated with fresh laundry. Musk is a very big molecule, for a smell, and it sticks really well to your clothes even as they’re being washed, so it’s the main ingredient in laundry detergents.

When you smell “clean laundry,” you don’t think you’re smelling musk, but you are. Funny how today we associate clean with a thing that ultimately comes from an animal’s butt. (Please note that today, most if not all musk comes from a laboratory and not an animal.)

Hyperosmia and the Elastic Mind

Design and the Elastic Mind, MOMA, 2008. James Auger and Jimmy Loizeau, Design Interactions Dept., Royal College of Art. 

Penicillium Saprophyticus is a kind of mold that comes around in autumn, when the living tissue of the woodlands begins its seasonal decomposition. At the helm of the HMS Entropy are the roaming swarms of saprophytes that live off of dying plants. In small doses their smell can be intoxicating. The haunting smell of crushed leaves in autumn is not without a touch of this mold.

Just as the seasons, weather events bring their own aromatic indicators. The smell when it’s about to snow, river musk on now-dry floodplains after a severe summer flooding, the smell of the beach on the same floodplains after severe hurricane flooding, and plenty of mold during a mismatching of seasonal characteristics – these all announce the ever-changing and rebirthing of an ecosystem. 

Some people smell strongly of civet, some simply have evaporated cat piss all over them, and sometimes it’s hard to tell the difference. Civet, like lots of smells, is good at low doses, but bad when high, and people become desensitized over time. Many perfumes use civet, on purpose, for this reason. Many grandmothers are avoided, for the same. (Blackcurrant buds give off the same smell, and are used in perfumery.)

Furfural mercaptans are strong – coffee, cannabis, skunkpiss. They intermingle, both in molecular presence, and redintegrated perception. In a classroom, one might smell diesel exhaust, barely perceptible, somehow coming through a labyrinth of antiquated air vents.

Then there is the smell of lactose being processed in the body, on a scale from skim milk, through butter, to mozzarella cheese. Poison ivy (which I get every August) smells like something, though I cannot name it – it is the smell of my own body metabolizing urushiol.

Notes:

Where Science and Design Collide, a Few Weird Sights to Behold

John Schwartz, February 26, 2008, nytimes

ART AND SCIENCE: The show “Design and the Elastic Mind,” at the Museum of Modern Art in New York, features items like “Smell +,” left, whose designer, James Auger, said he wanted to underscore the diminished importance the sense of smell had in our lives by creating a device that allowed people to smell each other’s bodily scents before they met.

http://www.nytimes.com/2008/02/26/science/26elas.html

Design and the Elastic Mind

Paola Antonelli, MoMA, 2008

http://www.moma.org/interactives/exhibitions/2008/elasticmind/

James Auger and Jimmy Loizeau

Design Interactions Dept., Royal College of Art, viaMoMA

http://moma.org/exhibitions/2008/elasticmind/#/237

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

coconut

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

Nonanal

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)

Acetone

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)

Indole

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

Skatole

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

Jasmine

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

trans-2-Nonenal

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

p-Cresol

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?).

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:

The human brain representation of odor identification

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).

Notes:

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.

On Very Large Databases

human metabolome database

The American Society for Biochemistry and Molecular Biology has this prescription for a periodic table of proteins, organizing protein complexes based on simple rules, tens of thousands of protein complexes each with their own 3-d structures, let us recall the hypothetical smell network of all possible smells as they occur to all people – the Lingua Anosmia.

There is a strong connection between olfaction and the growing databases of bioinformatics, because smells are organic entities themselves.

There is another database I envy, the human metabolome. It contains 40,000 entries, all the metabolites that exist within and among the human body. This one has even closer affinity with olfaction, because lots of metabolites smell; and if they don't smell, they are the molecules that eventually separate and combine to make something that does smell. Knowing the relationships among the molecules associated with smelly activity can help to organize the resulting smells of said metabolic activity. Your body odor does not come from your body - unless we consider our microbiome to be part of our body. Molecules that exit your body via sweat are deposited on the skin, a buffet plate for the colonies of bacteria that live with us. They eat your sweat and shit the body odor that you tend to consider yours. The smell of the beach is a secondary metabolite of seaweed, which means the same thing – sea bacteria eat the waste, or the metabolites, of seaweed.

Yes, that beautiful, intoxicating, deep and alluring scent of the seashore is to the ocean what body odor is to our bodies.

In conclusion, metabolites, and many things biological, and in their new supersized databasable format, are a step closer to the realization of the hypothetical smell network, the Lingua Anosmia.

I’d like to ask the driven and capable reader to hook-up this human metabolome with some smell data; I’d love to see it. Had I the time and expertise, I'd like to hook it up myself, but alas; it's on my list.

Post Script
Periodic Table of Proteins – University of Cambridge – Dec 2015

“We’re bringing a lot of order into the messy world of protein complexes”

-Sebastian Ahnert

Long form description of the Human Metabolomic Database:

The database is designed to contain or link three kinds of data: 1) chemical data, 2) clinical data, and 3) molecular biology/biochemistry data. The database contains 41,993 metabolite entries including both water-soluble and lipid soluble metabolites as well as metabolites that would be regarded as either abundant (> 1 uM) or relatively rare (< 1 nM). Additionally, 5,701 protein sequences are linked to these metabolite entries. Each MetaboCard entry contains more than 110 data fields with 2/3 of the information being devoted to chemical/clinical data and the other 1/3 devoted to enzymatic or biochemical data. Many data fields are hyperlinked to other databases (KEGG, PubChem, MetaCyc, ChEBI, PDB, UniProt, and GenBank) and a variety of structure and pathway viewing applets. The HMDB database supports extensive text, sequence, chemical structure and relational query searches. Four additional databases, DrugBank, T3DB, SMPDB andFooDB are also part of the HMDB suite of databases. DrugBank contains equivalent information on ~1600 drug and drug metabolites, T3DB contains information on ~3600 common toxins and environmental pollutants, SMPDB contains pathway diagrams for ~700 human metabolic and disease pathways, whileFooDB contains equivalent information on ~28,000 food components and food additives.

Citing the Human Metabolome Database:

1. Wishart DS, Tzur D, Knox C, et al., HMDB: the Human Metabolome Database. Nucleic Acids Res. 2007 Jan;35(Database issue):D521-6. 17202168

2. Wishart DS, Knox C, Guo AC, et al., HMDB: a knowledgebase for the human metabolome.Nucleic Acids Res. 2009 37(Database issue):D603-610. 18953024

3. Wishart DS, Jewison T, Guo AC, Wilson M, Knox C, et al., HMDB 3.0 — The Human Metabolome Database in 2013. Nucleic Acids Res. 2013. Jan 1;41(D1):D801-7. 23161693

Poison Ivy Smells

It's poison ivy season. I have it right now, just a little bit. When I get a lot, I can smell it, not the plant, but I smell it coming out of my skin, usually a day or so after I've been dosed, but before the itching starts to come out. At times, it's the smell that alerts me, and that I should stop itching; itching always seems to make it worse.

I should probably know this already, but I decided today to look it up - what does poison ivy metabolize to while in the body? In other words, what am I smelling.

First, poison ivy has within it a thing called urushiol. It's a sap running through the veins of the plant, and anything that disturbs the plant will release this stuff as microdroplets onto whatever surface it touches. A walking animal, a biting insect, a gust of wind, your dog, a soccer ball rolling on the ground, your lawn mower, or my favorite, a chainsaw ripping through a down sycamore with a hidden 3 inch vine of poison ivy growing on it, in October, can send the stuff wafting in the air as you ride your bike past its cloud of crystalized urushiol that then gets unwittingly lodged in your beard. (By the time I discovered what happened, days later, it was way too late to shave.) That's an extreme event; it usually happens in summer, unless you're doing some thorough spring cleaning, and it usually doesn't 'waft through the air,' unless it's been projected by a chainsaw.

So urushiol gets on your skin, then it gets absorbed into the outer layer of your skin, as all oils do. But then, something else happens to the oil. It enters the blood, and your body breaks it down into some other chemical that is seen as an invader, and your body starts to fight it, leaving you with the collateral damage, that being your red, itchy, peeling, maybe scabbing skin.*

But this is the part where it smells. The body breaks down urushiol into quinones, and the quinone chemicals give you the reaction. The quinones also give you that smell. I look for urushiol metabolites, find quinone, or 1,4-Benzoquinone to be specific, and look for odor properties.

And?

"chlorine, bleach, and hot plastic"

Wow, that's it. That's what poison ivy smells like when it comes out of your body. See if you can pick it out this season, a day or so after that camping trip, but before the histamine hijacking begins.


*The poison ivy reaction will only appear where the oil originally touched you. Even though it has to get into your blood to become active, the activated metabolites do not travel around the body and show up in other places at random. Instead, they stay where they contacted you initially. This process, where the urushiol is converted into reactive quinone, happens at different rates on different parts of the body, because the thickness of our skin varies. The palms of your hands will never get poison ivy because they're too thick. The skin on your face, however, is very sensitive, and if your whole body got covered in one day, your face would probably get it first, and your forearms would get it maybe two days later, making it seem like it's spreading around in your blood, but it's not.


Notes

Urushiol on Toxnet, the US Hazardous Substance Database:
https://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+7485

ancillary sources:
http://www.poison-ivy.org/
http://students.umw.edu/healthcenter/files/2011/08/Poison-Ivy.pdf

Terminology

synthetic urushiol:
5-methyl-3-n-pentadecylcatechol
(commonly called catechols)

urushiol metabolite:
1,4-Benzoquinone
(commonly known as para-quinone,or simply quinone)

Post Script

Some good random facts from the internet:

• Only 1 nanogram (billionth of a gram) is needed to cause a rash.
• The average exposure for most people is 100 nanograms.
• 1/4 oz. of urushiol is all that is needed to cause a rash in every person on earth.
• 500 people could itch from the amount covering the head of a pin.
• Specimens of urushiol several centuries old have been found to cause dermatitis
• in sensitive people.
• 1 to 5 years is normal for urushiol oil to stay active on any surface including
• dead plants.
• The name is derived from urushi, the Japanese name for lacquer

Artist Ingests and Sweats Dangerous Amount of Dye

Everything we consume eventually comes back out, and in other ways besides the most obvious. Many of the foods we eat are excreted through the skin via sweat, and lends itself to the many smells of body odor.

On a side note, the author can smell poison ivy being metabolized in his own body and excreted in this way. I can also tell the quality and type of milk product within 20 minutes after consumption - I might not notice "old butter" while I'm eating it on my toast, but I'll know soon enough. Gross. Milk smells not-so-much, and pizza cheese is the worst. I have a hard time finding people who know what I'm talking about, so if you do, please comment(!).

Post Script:

On transformative human effluence:

Scientist Christina Agapakis and olfactory artist Sissel Tolaas acquired and fermented human sweat to make cheese out of it. The big deal was the cheese made from Michael Pollan's stomach sweat (totally edible, even for vegans!).

link

And on the topic of disturbing performances:

Olivier de Sagazan's "Office Man", in the 2011 film Samsara, by Ron Fricke and Mark Magidson

video link

Suspense is in the Air and It’s Called Isoprene

Researchers investigated the air in movie theaters to learn how to predict the level of excitement in the show being watched. The revealing chemical patterns exhaled in this “crowd breath” are most clearly noted during suspenseful scenes in movies, and are consistent across multiple viewing audiences. The scientists say the rise in both CO2 and isoprene are a result of the accelerated breathing induced by a suspenseful movie scene.

Notes:

Suspense in the movie theatre air: Cinemagoers' exhaled breath reveals the scene that is playing

May 2016, phys.org

Jonathan Williams et al. Cinema audiences reproducibly vary the chemical composition of air during films, by broadcasting scene specific emissions on breath, Scientific Reports (2016). DOI: 10.1038/srep25464

Check Out the Axillary Glands on This One

Smell dating. Do me a favor and don’t take off that t-shirt for a few days. Get it all fumed-out. Now send it to us; we’ll cut it up into pieces and ship it out to potential mates. If they like what they smell, you’ve got yourself a date.

Yeah it's cute, but let's get something straight - when you choose a mate based on their armpits, it is your offspring that benefit, but not you necessarily.

Yes there is truth to this; it's pretty well-known: People tend to prefer the smell of others who have complementary immune systems. This makes your offspring have super-immune systems.

The thing is, it's not the Pleistocene anymore, and we don't have to choose mates based on major histocompatibility complexes via volatile metabolites. I mean, who said I even wanted to reproduce, I'm just looking for a date for this Friday, right?

In this case, smelling t-shirts is funny, but it's not so practical these days. Dating someone because of their MHC is like dating a robot because you like their algorithm.