When it Smells Like Team Spirit

Why do we connect and collaborate, deciding to "walk in the light of creative altruism" instead of the "darkness of destructive selfishness"?

Is it because of subtle behavioral clues that make us "click" and consider the other person a part of the group? Or is it because it smells like team spirit?

It very well might be. We (literally) smell love, victory, fear, along with chemicals that motivate us to cooperate. As was recently shown in double-blind placebo-controlled studies that quantitatively measured generosity and cooperation. Androstadienone, a rather unpleasant smelling molecule abundant in male sweat could make us more cooperative and more likely to think of the other person as "one of us". This molecule, created from male sex hormone testosterone possibly with the help of coryneform bacteria living under arms, was previously shown to have an effect on women - depending on social context and the time in their menstrual cycle. Even though androstadienone does not smell particularly plaasant - rather musky, with subtle urine-like and alcohol notes - merely smelling it is sufficient to maintain high levels of energy-boosting hormone cortisol  - possibly by inhibiting an enzyme (the 11β-hydroxysteroid dehydrogenase type 1 aka 11β-HSD1) responsible for its reactivation from cortisone.

Androstadienone

Androstadienone is related to another steroid estratetraenol found in the urine of pregnant women. Both molecules in large concentrations can affect mood -  improving it in females (also increasing their feeling of being focused and sensitivity to pain) while suppressing males. High testosterone males might even get depressed. So it might not be a good idea to sweat too much, but the right amount of sweating is actually helpful. If you are a male. When it comes to men deciding to cooperate with women, chemistry alone is less helpful. As in the old monkey experiment (Michael and Zumpe, 1982) where the best female strategy was to block male's access to other female monkeys. So, don't sweat it ladies. Just be dominant.

REFERENCES

Huoviala P, & Rantala MJ (2013). A Putative Human Pheromone, Androstadienone, Increases Cooperation between Men. PloS one, 8 (5) PMID: 23717389

Lundström JN, Hummel T, & Olsson MJ (2003). Individual differences in sensitivity to the odor of 4,16-androstadien-3-one. Chemical senses, 28 (7), 643-50 PMID: 14578126

 Michael RP, Zumpe D.  (1982) Influence of olfactory signals on the reproductive behaviour of social groups of rhesus monkeys (Macaca mulatta). J Endocrinol. 95(2):189-205. PMID: 7175415

Inhale and feel it with your heart

All you need is love. Or failing that chocolate.
And not only because dark chocolate could lower the risk of heart disease, blood pressure and sugar levels. As Dr. Schieberle's team recently discovered that heart could sense and enjoy the sweet smell of chocolate too. When they put small odor-emitting molecules from chocolate on one side of a dish, cells actually moved towards the aroma.

The heart, the lungs, the blood, the sperm and testis all have the abilities to recognize chemicals responsible for smells. Genomic studies (Deldmesser et al, 2006) showed that many tissues have working genes responsible for the perception of flavors. Sperm of sea urchines is able to recognize the odor and swim toward the egg. Human sperm might very well be capable of "smelling" their way to the egg too. And white blood cells sense the odors of bacteria to rush to the site of infection in the wound. Unfortunately, cancer cells can also sense their way out of the tumor in the direction of blood vessels, leading to metastasis. Smells can guide social preferences, trigger positive or negative memories, help to lose weight, reduce anxiety or give you nightmares. Smells can make or brake, kill or heal. They can have therapeutic or diagnostic use helping to understand gene-environment health paradigms and paving new avenues for future health care strategies.

REFERENCES

Feldmesser E, Olender T, Khen M, Yanai I, Ophir R, & Lancet D (2006). Widespread ectopic expression of olfactory receptor genes. BMC genomics, 7 PMID: 16716209

Schieberle P, & Molyneux RJ (2012). Quantitation of sensory-active and bioactive constituents of food: A Journal of Agricultural and Food Chemistry perspective. Journal of agricultural and food chemistry, 60 (10), 2404-8 PMID: 22369090

Schieberle P., Do cells in the blood, heart and lungs smell the food we eat? 245th  Chemistry of Energy and Food, National Meeting & Exposition of the American Chemical Society, New Orleans, LA, April 7-11, 2013

Odors and Infections

Many illnesses are associated with distinct odors. Especially those caused by infectious or opportunistic microbes inside the body or on its surfaces.  Body odor of someone infected with C. difficile, for example, can appear "swampy", Rotavirus gives sharply sweet putrid smell that some people associate with wet dogs. H. pylori can create a range of foul odors, and pseudomonas infections can smell like grapes and bitter almonds. 

Infections like C. difficile are usually linked to a general imbalance of the intestinal microbiota, often referred to as dysbiosis. This means that the odors could be coming from several microbial species, hence could be different for different individuals. Does it mean odor-based diagnostics will never be enough specific?

Not according to a 2-year-old beagle from Netherland, named Cliff. After just a little over two months of training, the beagle learned to identify the C. diff toxin by sniffing people or their samples. During one test, he was able to identify 25 out of 30 infected patients and 265 of 270 non-infected individuals. He also correctly identified 50 of 50 C. diff positive stool samples and 47 of 50 samples from people that did not have this infection. That's sensitivity of 100% for samples and 83-93% for sniffing the air around the patients, and a specificity of 94-100%! And it took him less than 10 minutes to accurately perform 300 diagnostic tests.  

Dogs already do the dirty work with detecting molds. They can examine an office building with 200 rooms in just 8 hours, a task that would take us several days of measuring  moisture, probably without any result. Electronic noses would be of great help and many years of research are finally being translated into useful technologies - to be integrated with refrigerators and mobile phones. But until we are able to build smart devices to detect odors without labor-intensive dog training, perhaps we could train our own nozzles. Studies have shown we do get better with practice. 


REFERENCES

Bomers MK, van Agtmael MA, Luik H, van Veen MC, Vandenbroucke-Grauls CM, & Smulders YM (2012). Using a dog's superior olfactory sensitivity to identify Clostridium difficile in stools and patients: proof of principle study. BMJ (Clinical research ed.), 345 PMID: 23241268

Poulton J, Tarlow MJ. (1987) Diagnosis of rotavirus gastroenteritis by smell. Arch Dis Child. 1987 Aug;62(8):851-2. PMID: 3662595

Arnaud Tognetti, Megan N Williams, Nathalie Lybert, Mats Lekander, John Axelsson, Mats J Olsson, Humans can detect axillary odor cues of an acute respiratory infection in others, Evolution, Medicine, and Public Health, Volume 11, Issue 1, 2023, Pages 219–228, https://doi.org/10.1093/emph/eoad016