Food, Hormones and Odor Pollution

While there is not enough research on human odors, there are plenty of studies that can be related to this topic. Scientific papers published in January are about goats, fish, fermented food and biological waste. 

It is worth examining some of the latest findings and how they may be translated into take-home messages for humans.

1. Intermittent fasting could improve body odor. 

At least for fish. The study aimed to investigate the response of intestinal microbiota during 3 weeks’ starvation of largemouth bass (Micropterus salmoides), found that food deprivation helped to improve the odor of an economically important freshwater fish by reducing earthy-musty off-flavor compounds such as geosmin and 2-methylisoborneol. The study revealed that certain actinobacteria such as Microbacterium and Nocardioides were able to grow better than Mycoplasma, Pseudomonas, Acinetobacter, and Microbacterium when the fish were in a fasted state. This suggests that intermittent fasting may help to improve body odor by promoting the growth of beneficial bacteria and reducing the growth of odor-causing bacteria. However, more research is needed to confirm these findings in human studies. Besides, our own data show that people smell worse when starving themselves and it is a good idea to not go overboard. 

2. Adding fiber to diet and reducing stress levels can improve body odor. 

Korean native black goats (KNBG) are able to adapt to a wide variety of climatic conditions and foraging preferences. Twenty-four KNBG (48.6 ± 1.4 kg) were randomly allocated to one of four treatments featuring different dietary forage (high in fiber) to concentrate ratio (high forage [HF, 80:20] and low forage [LF, 20:80]), and a castration treatment (castration [CA] vs. non-castration [NCA] - aka higher levels of sex hormones, stress hormones). The animals were maintained on a free-choice feed and water regimen.

The intensity of a strong “goaty” flavor was remarkably enhanced when non-castrated KNBG were fed with the low forage diet. Better smelling goats had more hydrocarbons and ketones while worse smelling ones were higher in aliphatic aldehydes, possibly owing to the activity of testosterone, androsterone, and skatole. For volatile compounds, dichloromethane (chloroform-like odor) and m-xylene (plastic odor) were reported to be linked with the “strong lamb odor” influenced by dietary selection. 

10% fermented mixed feed supplementation (compared to 5% or 0%) helped to improve flavor of pork by increasing the contents of total aldehydes, (E,E)-2,4-nonadienal, dodecanal, nonanal and 2-decenal, along with inosine monophosphate. 

A healthy gut microbiome may positively influence sex hormones by regulating the appetite and reducing insulin resistance. Acute psychosocial stress, on the other hand, causes unhealthy fluctuations in sex hormone levels.  

Here are a few tables compiled from the goat diet/hormones article:

Microbe Genus	Compounds positively correlated	Compounds negatively correlated.
Flexilinea	C16:0 (Palmitic acid, oily smell)	C18:2n6 (Methyl linoleate, oily odor), C18:3n3 (Linoleic acid, oily, low odor), PUFA
Ihubacter	C16:0 (Palmitic acid, oily smell)	C18:2n6, C18:3n3 (Linoleic acid), PUFA
Ruminococcus	-	C16:0 (Palmitic acid, oily smell)
Christensenella	C18:0 (Stearic acid), PUFA	C16:1n7 (Palmitoleic Acid, Cardioprotective - smells like Old Books)
Lachnoclostridium	C18:1n9 Oleic acid)	C18:2n6, C18:3n3 (Linoleic acid),, PUFA
Treponema	-	C18:0 (Stearic acid), C18:3n3 (Linoleic acid), C20:4n6 (Arachidonic acid: from marine, at low concentrations, to intense orange-citrus and animal-like odor)
Succiniclasticum	C18:1n7 (Vaccenic acid), C18:3n3 (Linoleic acid)	-
Desulfovibrio	C18:1n7 (Vaccenic acid)	-
Blautia	-	C18:2n6 (Linolelaidic acid)
Rhabdanaerobium	-	C18:3n3 (Linoleic acid)
Gracilibacter	-	C18:3n3 (Linoleic acid)
Butyrivibrio	-	C18:3n3 (Linoleic acid)
Paraprevotella	C20:4n6, C22:4n6	-
Intestinimonas	C22:4n6	-

This table summarizes the relationship between meat fatty- composition and rumen bacteria at the genus level. 

Higher levels of carbohydrates may promote the persistence and flavor formation of Z. rouxii (Zygosaccharomyces, a genus of yeasts in the family Saccharomycetaceae) in the moromi soy sauce, and it changes its aroma profile. Not sure if it is to the better or worse. 

3. Acinetobacter is associated with fish odor and the odor of biowaste. It is also associated with odor in MEBO and PATM populations - this is one of not yet published results of our microbiome study  (in addition to skin bacteria)

A study to be published in print in the February issue of "Science of The Total Environment", examined odor profiles of cooked and uncooked food waste.

Odor pollution often occurs in the initial decomposition stage of municipal biowaste, including throwing/collection and transportation. However, this aspect of odor impact from municipal biowaste has not been well studied. In Nie and colleagues' experiments, a practical dustbin (120 L) equipped with flux chamber and filled with three types of municipal biowaste was used to simulate garbage storage conditions. The result indicated that the emission rate of odor pollutants for uncooked food waste (UFW) represented a nearly linear growth trend, reaching the maximum (3963 ± 149 μg kg−1 DM h−1) at 72 h. Cooked food waste (CFW) increased rapidly from 8 h to 24 h, and then remain fluctuated, reached the maximum (2026 ± 77 μg kg−1 DM h−1) at 72 h. Comparatively, household kitchen waste (HKW) reached the maximum emission rate (10,396 ± 363 μg kg−1 DM h−1) at 16 h. Sulfide and aldehydes ketones were identified as dominant odor contributor to UFW and CFW, respectively. While aldehydes ketones and sulfides were both dominant odor contributor to HKW. Moreover, the microbial diversity analysis suggests that Acinetobacter was the dominant genus in UFW, and Lactobacillus was the dominant genus in CFW and HKW. In addition, it was evident that each odorous pollutant was significantly associated with two or more bacterial genera, and most bacterial genera such as Acinetobacter, were also significantly associated with multiple odorous pollutants. The variation of odorants composition kept consistent with microbial composition. The present study could provide essential evidence for a comprehensive understanding of odorant generation in the initial decomposition stage of municipal biowaste. It could contribute to setting out strategies for odor control and abatement in municipal biowaste management systems.

The highest emission was observed in household kitchen waste with alcohol esters.

The highest total odor activity values were observed in uncooked food waste.

Lactobacillus was the dominant genus in household kitchen waste and cooked food waste.

Acinetobacter was the dominant genus in uncooked food waste. 

The variation of odorants composition kept consistent with microbial composition.

REFERENCES

Lee J, Kim HJ, Lee SS, Kim KW, Kim DK, Lee SH, Lee ED, Choi BH, Barido FH, Jang A. Effects of diet and castration on fatty acid composition and volatile compounds in the meat of Korean native black goats. Anim Biosci. 2023 Jan 11. doi: 10.5713/ab.22.0378. Epub ahead of print. PMID: 36634653. download pdf

Zou S, Ni M, Liu M, Xu Q, Zhou D, Gu Z, Yuan J. Starvation alters gut microbiome and mitigates off-flavors in largemouth bass (Micropterus salmoides). Folia Microbiologica. 2023 Jan 13:1-2.

Lülf RH, Selg-Mann K, Hoffmann T, Zheng T, Schirmer M, Ehrmann MA. Carbohydrate Sources Influence the Microbiota and Flavour Profile of a Lupine-Based Moromi Fermentation. Foods. 2023 Jan 2;12(1):197. doi: 10.3390/foods12010197. PMID: 36613413; PMCID: PMC9818829.

Nie E, Wang W, Duan H, Zhang H, He P, Lü F. Emission of odor pollutants and variation in microbial community during the initial decomposition stage of municipal biowaste. Sci Total Environ. 2023 Feb 25;861:160612. doi: 10.1016/j.scitotenv.2022.160612. Epub 2022 Nov 29. PMID: 36455726.

Shi Q, Tang X, Liu BQ, Liu WH, Li H, Luo YY. Correlation between microbial communities and key odourants in fermented capsicum inoculated with Pediococcus pentosaceus and Cyberlindnera rhodanensis. J Sci Food Agric. 2023 Feb;103(3):1139-1151. doi: 10.1002/jsfa.12321. Epub 2022 Nov 24. PMID: 36349455.

Gabashvili IS Cutaneous Bacteria in the Gut Microbiome as Biomarkers of Systemic Malodor and People Are Allergic to Me (PATM) Conditions: Insights From a Virtually Conducted Clinical Trial JMIR Dermatol 2020;3(1):e10508 doi:  10.2196/10508

Search Odors (cdc.gov) - database of toxic chemicals

OdorDB: Home (yale.edu)

Olfactory Signatures and COVID-19

Olfactory disorders have a significant impact on human lives - be it a lost/distorted sense of smell or unpleasant odors affecting the sense of smell of others. 

Odortypes can be influenced by human leukocyte antigen (HLA) genes of the major histocompatibility complex (MHC), genes associated with stronger response to COVID-19 vaccine as well as the severity of this disease. HLA may also be related to people's perception of the odor of other people. 

Of course, these are not the only variables involved, and there are more potentially overlapping risk factors for olfaction, metabolic body odor (MEBO), including trimethylaminuria (TMAU), and COVID-19: FMO3, SELENBP1, HspA, UGT2A1/UGT2A2, etc. 

A new peer-reviewed paper reporting results of a decentralized observational study (NCT04832932) compared MEBO participants to general populations in respect to their response to COVID-19 vaccines and SARS-Co-V2 infections. 

Body odor flareups were observed in about 10% of malodor sufferers after vaccination, as preliminarily reported. This number was similar to flareups of other chronic symptoms in groups of participants with gastrointestinal and autoimmune disorders.  

Long-term worsening of body odor was observed by other researchers after COVID-19 vaccination in about ~1% of studied populations. Dry mouth leading to halitosis was 10 times more prevalent compared to flu vaccines. MEBO participants reported stronger reactions than general population pointing to genetic and microbiome influences beyond FMO3.  

A better understanding of systemic malodor conditions could offer leads for targeted therapies. Findings on genetic and microbiome overlaps between COVID-19 and MEBO could pave the way for precision medicine to address the unmet needs of odor sufferers.

REFERENCE

Gabashvili IS. The Incidence and Effect of Adverse Events Due to COVID-19 Vaccines on Breakthrough Infections: Decentralized Observational Study With Underrepresented Groups. JMIR Formative Research. 2022 Nov;6(11):e41914. DOI: 10.2196/41914. PMID: 36309347; PMCID: PMC9640199.

Post-infectious body odor

Every infection has a distinct odor. It could be associated with changes in the gut microbiome. Besides, circulating B-cells from our immune system are also producing chemical odors that appear after viral infection. T-cell and cytokine involvement is also possible. Infections can change body odor for the worse.  PATM or MEBO conditions could begin after an infection and linger thereafter.  

COVID-19 is known to be associated with a specific odor.  Early studies identified volatile compounds that discriminated COVID-19 from other conditions. Some of these compounds - such as fruity smelling ketones - are also associated with diabetes - a risk factor for Severe COVID-19 infection. Another compound, Heptanal, associated with lung cancer, can also predict the severity of the Coronavirus disease.

Dogs (and rats and other animals) can easily detect the smell of COVID-19. They are already helping during this pandemic - Massachusetts schools, for example, are using dogs to sniff out Covid-19. The dogs come to the schools weekly and work to detect cases in empty classrooms, auditoriums, cafeterias and gymnasiums, If Covid is detected, the authorities tell the health nurse who relays the information to the people affected.

Long COVID - when people continue to have symptoms of COVID-19 for months after their initial illness. - has a distinct smell as well. A paper posted today on MedRxiv tells that dogs can easily detect long COVID as well - in at least half of the cases. 

Between May and October 2021, 45 Long COVID patients sent their axillary sweat samples to the National Veterinary School of Alfort. Average age of the patients was 45 (6-71) and 73.3% were female. No patient had been admitted in intensive care unit during the acute phase. Prolonged symptoms had been evolving for an average of 15.2 months (range: 5-22). Main symptoms of prolonged phase were intense fatigue (n=37, 82.2%), neurocognitive disorders such as concentration and attention difficulties, immediate memory loss (n=24, 53.3%), myalgias/arthralgias (n=22, 48.9%), cardiopulmonary symptoms (dyspnea, cough, chest pain, palpitations) (n=21, 46.7%), digestive symptoms (diarrhea, abdominal pain, reflux, gastroparesis...) (n=18, 40.0%), ENT disorders (hyposmia, parosmia, tinnitus, nasal obstruction, inflammatory tongue, dysphonia, sinusitis) (n=18, 40.0%) (table 1). 11 (24.4) patients had at least one positive SARS-CoV-2 serology before any vaccination, 29 (64.4%) had a negative SARS-CoV-2 serology and 5 (11.1%) had no serology results. Snapshot of the table shows some of the cases. Interestingly, patients with odor exhibited symptoms similar to long COVID sufferers in the MEBO community. This includes loss of smell and heart palpitations. 

REFERENCES

Dominique GRANDJEAN, Dorsaf SLAMA, Capucine GALLET, Clothilde JULIEN, Emilie SEYRAT, Marc BLONDOT, Maissa BENAZAZIEZ, Judith ELBAZ, Dominique SALMON Screening for SARS-CoV-2 persistence in Long COVID patients using sniffer dogs and scents from axillary sweats samples  medRxiv 2022.01.11.21268036; doi: https://doi.org/10.1101/2022.01.11.21268036

Worried about body odor?

You are not alone. According to pre-COVID surveys, over one third said the fear of smelling unpleasant left them feeling unhappy and unattractive. Many people who survived COVID-19 worry about their body odor getting worse post-infection.

A team of researchers from Virginia Commonwealth University surveyed 322 individuals with loss of smell or taste as a result of confirmed COVID-19 infection and found that about half of them felt depressed and worried about their body odor [Coelho et al., 2021].  Extrapolating results of other surveys, this translates into about 20% of those who got through COVID-19.  

The most frequently reported phantom smell (likely not actually there) is the odor of smoke or burned food [Frasnelli et al, 2004]. Interestingly, these are also the most frequently reported types of smells that long-COVID sufferers can't perceive, when others detect them. 

Temporary loss of smell is common. About 20% of population experience it sometime before the age of 75. This number increases to ~80% in older age. 

Loss of smell associated with viral infections, especially COVID-19 is much more prevalent. Sometimes it's the only symptom associated with this infection. A meta-analysis of published reports reveals that the overall prevalence of alteration of the sense of smell or taste following COVID-19 infection ranges between 31% and 67% in severe and mild-to-moderate symptomatic patients, respectively. Fortunately, in most (70-80%) cases it comes back in 6 month or longer. A higher recovery rate was highlighted for subjects who underwent influenza vaccination. 

REFERENCES

Coelho DH, Reiter ER, Budd SG, Shin Y, Kons ZA, Costanzo RM. Quality of life and safety impact of COVID-19 associated smell and taste disturbances. American Journal of Otolaryngology. 2021 Jul 1;42(4):103001.

Frasnelli J, Landis BN, Heilmann S, Hauswald B, Hüttenbrink KB, Lacroix JS, Leopold DA, Hummel T. Clinical presentation of qualitative olfactory dysfunction. European Archives of Oto-Rhino-Laryngology and Head & Neck. 2004 Aug;261(7):411-5. 

Maiorano E, Calastri A, Robotti C, Cassaniti I, Baldanti F, Zuccaro V, Stellin E, Ferretti VV, Klersy C, Benazzo M. Clinical, virological and immunological evolution of the olfactory and gustatory dysfunction in COVID-19. American Journal of Otolaryngology. 2022 Jan 1;43(1):103170.

Vaira LA, De Vito A, Lechien JR, Chiesa‐Estomba CM, Mayo‐Yàñez M, Calvo‐Henrìquez C, Saussez S, Madeddu G, Babudieri S, Boscolo‐Rizzo P, Hopkins C. New onset of smell and taste loss are common findings also in patients with symptomatic COVID‐19 after complete vaccination. The Laryngoscope. 2021 Nov 26.

COVID-19 and vaccine reactogenicity in MEBO/PATM community

Infections have been shown to alter body odor and so have immunizations. So far, only nonhuman animals were able to detect the subtle changes in chemical makeup after vaccinations and even their sensitive noses were not able to differentiate between different vaccines - such as the rabies virus or the West Nile virus vaccines [Kimball et al, 2014]. However, this was the case of very mild reactions to immunization. Even slightly stronger inflammatory responses, to relatively weak immune challenges, can, indeed, be detected by human noses [Gordon et al, 2018]. Urine and axillary odor are becoming slightly more aversive in healthy humans, as a function of immune activation. But this is not supposed to last too long.

Our preliminary results, based on responses to the survey for 24 members of MEBO community and 6 of their family members show a wide variety of reactions to Astrazeneca, J&J, Moderna, Pfizer and Sinovac/Coronavac vaccines. 

Interestingly, Pfizer vaccine that caused no or very mild reactions in several MEBO participants, was also the vaccine that possibly caused temporary worsening of odor symptoms in one person in the community. Another MEBO participant that reported possible worsening of odor from Moderna vaccine had one thing in common with the other individual - they both had pre-existing conditions related to their upper digestive tract. Some Astrazeneca recipients also reported odor issues but did not think it was worse than usual. 

One of the most interesting observations was that even though only 2 members of MEBO/PATM community reported COVID-19 infection (before or between vaccinations), both of them had long COVID with long-term neurological manifestations such as fatigue, ENT symptoms and loss of smell.

Adverse reactions to COVID-19 vaccines are influenced by a multitude of factors, many of which can be anticipated and alleviated. A certain level of inflammation is needed to trigger an effective adaptive immune response, but both environment and genetic makeup determine who is more likely to experience particular symptoms after infection and from the vaccine.

You can help by telling us about your experiences with COVID-19 and/or vaccinations. These surveys can be used for posting your brief stories - no need to answer all the questions. And you can always add to your story later. Please use your anonymous ID and let us know if you have any questions.

Survey

in English:  https://bit.ly/BTN-eng

en Español: https:/bit.ly/BTN-esp

We'll be posting more observations and comparisons with over 600 participants of our study from other communities. 

REFERENCES

Blumental S, Debré P. Challenges and issues of anti-SARS-CoV-2 vaccines. Frontiers in Medicine. 2021;8.

Gordon AR, Kimball BA, Sorjonen K, Karshikoff B, Axelsson J, Lekander M, Lundström JN, Olsson MJ. Detection of inflammation via volatile cues in human urine. Chemical senses. 2018 Nov 1;43(9):711-9.

Kimball BA, Opiekun M, Yamazaki K, Beauchamp GK. Immunization alters body odor. Physiology & behavior. 2014 Apr 10;128:80-5.

Vaccine to cure body odor?

There could be a vaccine for everything. Scientists are working on personal vaccines, vaccines reducing body weight or narcotic dependence, vaccines for just about anything.  Can there be a vaccine improving body odor? Certainly, and it could target not only bacteria (in body crevices) worsening odor, but also molecules responsible for odor. This would be a very complex task, however, as there is still a lot we don't understand.  For example, if metabolism and microbiomes leading to body odor cause similar reactions to already existing vaccines. 

Several vaccines to prevent COVID-19 were authorized for emergency use and hundreds of millions doses have been administered. 2 millions of vaccinated individuals in the US completed a health survey in the 7 days following their vaccination via the v-safe app.

This table shows top adverse reactions reported to the first two vaccines authorized in the US. Hundreds of social media groups on Facebook, reddit and WhatsApp are also flooded by descriptions of adverse reactions and immunity related events. What is missing? The ability to systematically analyze all these reactions in different health and neighborhood communities.

We started such a study in one neighborhood community and would like to also conduct it in the MEBO/PATM communities. We are also opening it to MEBO friends and family - asking them to indicate their relationship with MEBO/PATM in the comment section of the survey.

We are also collecting COVID-19 experiences in different groups of people, analyzing infectious disease susceptibility risks. 

in English: https://bit.ly/BTN-eng

en Español: https:/bit.ly/BTN-esp

Thank you for your help!

REFERENCES

ClinicalTrials.gov [Internet]. Bethesda (MD): National Library of Medicine (US). 2021 April 6 - . Identifier NCT04832932, The COVID-19 Back-to-Normal Study [cited 2021 April 7]; Available from: https://clinicaltrials.gov/ct2/show/NCT04832932

Chapin-Bardales J, Gee J, Myers T. Reactogenicity Following Receipt of mRNA-Based COVID-19 Vaccines. JAMA. 2021 Apr 5. doi: 10.1001/jama.2021.5374. Epub ahead of print. PMID: 33818592. 

Zimmermann P, Curtis N. Factors that influence the immune response to vaccination. Clinical microbiology reviews. 2019 Mar 20;32(2). 

Mosquera MJ, Kim S, Zhou H, Jing TT, Luna M, Guss JD, Reddy P, Lai K, Leifer CA, Brito IL, Hernandez CJ. Immunomodulatory nanogels overcome restricted immunity in a murine model of gut microbiome–mediated metabolic syndrome. Science advances. 2019 Mar 1;5(3):eaav9788.

Bandaru P, Rajkumar H, Nappanveettil G. The impact of obesity on immune response to infection and vaccine: an insight into plausible mechanisms. Endocrinol Metab Synd. 2013;2(2):1000113-22. 

Kim YH, Kim JK, Kim DJ, Nam JH, Shim SM, Choi YK, Lee CH, Poo H. Diet-induced obesity dramatically reduces the efficacy of a 2009 pandemic H1N1 vaccine in a mouse model. Journal of Infectious Diseases. 2012 Jan 15;205(2):244-51. 

 Monteiro MP. Obesity vaccines. Hum Vaccin Immunother. 2014;10(4):887-95. doi: 10.4161/hv.27537. Epub 2013 Dec 23. PMID: 24365968; PMCID: PMC4896563. 

Ozgen MH, Blume S. The continuing search for an addiction vaccine. Vaccine. 2019 Aug 23;37(36):5485-90. 

Daniel W, Nivet M, Warner J, Podolsky DK. Early evidence of the effect of SARS-CoV-2 vaccine at one medical center. New England Journal of Medicine. 2021 Mar 23.

Microbial diagnostics of MEBO

There are many medical conditions for which there are no standard tests for definite diagnosis and no established cures.  Diagnosing and curing Metabolic Body Odor (MEBO) is even more difficult. Especially because MEBO is an umbrella term for several different conditions.

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Gender - confounder of concern?

Background and clinical characteristics measured at baseline are comparable in the groups of our study. But this doesn't eliminate the need to investigate the impact of confounding. We've already analyzed the effects of age, What about gender as a potential confounder?

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Reducing the stigma of odor disorders

Some conditions - such as obesity, depression and functional odor disorders - come with a social stigma. Understanding the etiology of these conditions helps to avoid stereotypes and find remedies. 

Metabolomics analysis of morning urine samples helped to evaluate the heterogeneity of MEBO population as good as challenge tests, procedures used to induce symptoms and assess resilience to perturbations caused by sugars. 


...  Read more ... 

Microbes of anti-social odor

Human odors depend on many extrinsic (such as food or clothing) and intrinsic factors - localized or systemic. In recent years, microbes responsible for localized malodors - bad breath caused by oral bacteria and axillary odor - have been mapped by using next generation sequencing approaches. However, intestinal microbes responsible for systemic malodor (whole-body and extraoral halitosis), remain to be identified.

 Our preliminary analysis of culture-, PCR- and 16S-RNA-based data donated by MEBO and PATM community members show that there are no easy answers.

Unraveling the Mysteries of Mischievous Microbiome

Science explains why some people smell worse than others despite keeping themselves squeaky clean.


  
The body is crawling with microbes that have evolved with the person, depending on the innate metabolism, history of infections, microbiome swaps, diet and lifestyle. The body's ecosystem of microorganisms can increase the risk for dangerous diseases for which we have unreserved levels of sympathy. It can also lead to ​unlikable conditions such as unpredictable and embarrassing outbursts of odor emitting through the pores - odor so bad it ruins social lives and careers.

Let those who never smelled bad cast the first stone

Analysis of our metabolism is crucial to comprehending the responses of our genes and microbes to the stresses of daily life, and to elucidating the causes and consequences of health and disease.

We applied metabolomic approach to an elusive condition that has always evaded diagnosis: socially and psychologically distressing odors that occur without a known or apparent cause. Learn about our preliminary results and participate in our anonymous survey to help us better understand and help with this condition.

Giving the underserved the care they deserve

Nobody likes strong smells coming from other human beings. It's just that social convention: you are nice, if you smell nice, and you are a monster - like Shakespeare's Caliban - if you smell bad.

But it could be the brunt of the genetic or environmental misfortune

Body Odor and Skin Bacteria

Our bodies are rainforests of microbes feeding off the leftovers from our meals and contributing to a variety of body odors. 

Human skin is inhabited and re-populated depending on health conditions, age, genetics, diet, the weather and climate zones, occupations, cosmetics, soaps, hygienic products and moisturizers. All these factors contribute to the variation in the types of microbes. Population of viruses, for example, can include a mixture of good ones - like bacteriophages fighting acne-causing Propionibacterium  - and bad ones  - as highly contagious Mesles. Bacterial communities include thousands of species of Actinobacteria, Bacteroidetes, Cyanobacteria, Proteobacteria, and fungi Malassezia.

Nat Rev Microbiol. 2011 April; 9(4): 244–253.

Nat Rev Microbiol. 2011 April; 9(4): 244–253.

These microbes form communities and have active social lives, cooperating to our good and bad experiences. They converse chemically - in many specific dialects and in universal Esperanto-like languages some of which even we could listen to  - by sampling and understanding smells. 

Humans are among the smelliest animals. And very capable in telling smells apart,  even if the only difference in two molecules is that their structures are mirror images of one another. But unlike dogs that appreciate a garbage bin as much as we appreciate the smell of fresh flowers, we don't properly interpret smells and like to complain about body odors. As we don't know all that much about chemical nature of our surroundings and rely on context and psychological factors, like feeling an intrusion in our experiences of the world. 

Maybe we have something to learn from the science of smells? 

In  a recent review of axillary microbiota, German researchers gave a good lesson in organic chemistry, listing major chemicals, enzymes and microbes responsible for body odor. Let's take a look. 

As was also shown in previous studies, Staphylococcus and Corynebacterium spp. are the most abundant organisms colonizing moist areas and emitting chicken-sulfury, onion-like and clary-sage like odors. The strain of Staphylococcus haemolyticus is producing some of the most offensive sulfury smells. Corynebacterium jeikeium K411 is another species that can compete on the strength of the odor. 

The major odor-causing substances are sulphanyl alkanols, steroid derivatives and short volatile branched-chain fatty acids. 

Most common sulphanyl alkanol in human sweat, 3-methyl-3-sulfanylhexan-1-ol is produced by bacteria in several ways, particularly in glutathione biodetoxification pathway, from molecules synthesized after consuming proteins (due to aminoacids L-cysteine, L-glutamic acid and glycin). This chemical,  besides being a major descriptor of human sweat odor,  is also present in beers. Its S-enantiomer (75%) is described as a classical body odor (sweat) with onion-like tones. Interestingly, the opposite enantiomer, (R)-3-methyl-3-sulfanylhexan-1-ol, is fruity and grapefruit-like. 

Another set of molecules produced by Corinebacterium are most prominent in Caucasian men and some Asians. The odor is hircine - resembling of goats with fatty and cheesy notes or cumin-spice like. The food sources contributing to this odor are proteins and animal fats. 

Pheromones androstenol and androstenone, metabolites of sexual hormones, are also odorous. The latter is especially interesting as to some of us it smells like vanilla while to others is smells like urine.

Sweaty-feet and cheesy smelling isovaleric and propionic acids and sour-vinegary acetic acid are also adding to the spectrum of human odors.  They can smell different to different people too - some people have genetic makeup making them hypersensitive to these smells, but others are much more tolerant and forgiving. The food sources of sourish smells are protein-rich. Lactic acid is found in cheeses, yogurt, soy sauce, sourdough, meats and pickled vegetables. It can be also produced from the breakdown of carbohydrates during exercise and used as additional fuel. Glycerol is created from triglycerides found in fats and oils.  

So next time you are exposed to body odor, try to understand what could be causing it. It is not easy as it is a combination of many factors such as hormonal fluctuations, mental or physical stress, metabolism and microbes. It could be perfectly normal or result from a medical condition of the person who has the smell and your own olfactory abilities. But the smells are fascinating clues to health and  the basics can be learned by most everyone.

REFERENCES

Fredrich E, Barzantny H, Brune I, & Tauch A (2013). Daily battle against body odor: towards the activity of the axillary microbiota. Trends in microbiology, 21 (6), 305-12 PMID: 23566668

Grice EA, & Segre JA (2012). The human microbiome: our second genome. Annual review of genomics and human genetics, 13, 151-70 PMID: 22703178

Stevenson, R., & Repacholi, B. (2005). Does the source of an interpersonal odour affect disgust? A disease risk model and its alternatives. European Journal of Social Psychology, 35 (3), 375-401 DOI: 10.1002/ejsp.263

Troccaz M, Starkenmann C, Niclass Y, van de Waal M, Clark AJ.  ( 2004) 3-Methyl-3-sulfanylhexan-1-ol as a major descriptor for the human axilla-sweat odour profile.Chem Biodivers. 2004 Jul;1(7):1022-35. PMID: 17191896

Lenochová P, Vohnoutová P, Roberts SC, Oberzaucher E, Grammer K, Havlíček J (2012) Psychology of fragrance use: perception of individual odor and perfume blends reveals a mechanism for idiosyncratic effects on fragrance choice. (PMID:22470479) Free full text article  PLoS One [2012, 7(3):e33810]

Barzantny H, Brune I, Tauch A. (2012) Molecular basis of human body odour formation: insights deduced from corynebacterial genome sequences. Int J Cosmet Sci. 2012 Feb;34(1):2-11. doi: 10.1111/j.1468-2494.2011.00669.x. Epub 2011 Jul 25.  PMID: 21790661