The ABCs of BO

For some reason that remains unclear, body odor is associated with sweat. This is unfair to people who exercise, undertake physical activities, or perform work that provokes the sweat of one’s brow… or just live in regions where the weather is hot and humid. Indeed, sweat is odorless, and its secretion is meant to have a cooling effect as well as to lubricate those parts of the body that might undergo friction in the course of the physical activity, mainly the armpits and the anogenital area.

So, why is sweat indicated as the culprit in body odor?

What happens is that our skin harbors a variety of microorganisms, the so-called skin microbiome, some of which have enzymes such as cysteine-thiol lyase able to digest the odorless, non-volatile components of sweat and generate thioalcohols, volatile, malodorant end products.^1,2 This happens on the skin itself as well as in the t-shirts and other fabrics that have been in contact with the body.  

Body Odor Biochemistry

While the chemical composition of sweat is independent of gender, different microorganisms are found in the armpits of males and females: in males there is a preponderant population of Corynebacterium jeikeium, whereas female armpits are mainly populated by Staphylococcus hominis. These bacteria have different enzymatic endowments, and this is the main reason why men and women armpits give out different smells (cheese/rancid versus fruity/onion). Interestingly enough, the skin colonizer Staphylococcus aureus is unable to generate smelly molecules but, when cloned with the gene of cysteine-thiol lyase from Staphylococcus hominis, it acquires the capability to produce malodorant molecules.³ 

The microbiome contains thousands of different microorganisms with different enzymatic panoplies, and the human body undergoes different hormonal situations while passing from childhood to puberty to teenager to young adult to menopause. Of course, stressful situations, illnesses and pathologies also impact the microbiome. Human body secretions are incredibly variable, and it is virtually impossible to predict what kind of body odor one will have in a given temporal and social situation. As a matter of fact, in addition to the axillary region, the feet and the anogenital area can be source of peculiar smells. 

Normal vaginal secretions are odorless or nearly odorless and have a yogurt-like smell. Thus, cheesy or fishy odor released with reproductive fluids might be a symptom of infections located in the genital area. Normal vaginal odors are reported to depend on the local pH that might affect the composition of the microflora and therefore the outcome of the metabolism of sweat and sebum, whereas a hint of ammonia can just relate to traces of urine.

Feet can smell when they are colonized by bacteria such as Bacillus subtilis, and in these cases, thorough washing can eliminate the undesired situation. In other instances, some bacteria carve visible niches in the skin between the toes, colonize the region, are impervious to being removed by simple washings and require treating skin, socks and shoes with antibiotic powders and lotions.

Avoiding Body Odors

Diet affects body odor, the most striking example is offered by the consumption of garlic and, to a lesser extent, of onions, cabbage, broccoli and cauliflower. The same is true for some spices like curry and cumin. In the case of food-derived body odors, one can either avoid eating those edibles or mask them with fragrances. 

In the case of body odors originating from metabolized sweat, the skin care industry offers deodorants and antiperspirants. 

Deodorants are fragrances embedded in lotion or sticks and can mask the unwanted odor. They can also be added with bacterio-static agents that limit or block the growth of odor-generating bacteria, such as triclosan. 

Antiperspirants are OTC drugs that contain metallic salts (usually Aluminum-Zirconium Salts). The most widely used active ingredients in antiperspirants are metallic salts. Aluminum Zirconium Trichlorohydrex Gly, a complex of the amino acid Glycine with C2H8AlClNO4Zr+5 , is a widely used active ingredient in antiperspirants. It is said to form polymers that clog the pores and hinder sweat from leaving the sweat duct. 

Clinical strength antiperspirants contain higher concentrations of the active ingredients than “regular” strength OTC antiperspirants. Prescription and specialty antiperspirants that contain aluminum chloride hexahydrate as an active ingredient are among the most effective antiperspirants. Unfortunately, they can cause skin irritation. Typically, aluminum chloride hexahydrate concentrations of 10% to 15% are recommended for inhibit sweat in the axillary pits. For managing excessive sweat of hands or feet, higher concentrations are needed—usually around 30%.

Conclusion

An exhaustive review has recently been published⁴ that considers all the anatomical sites that are sources of bad odors, tracks down the various types of odors that are met in humans and relates them to various pathologies or to microbiome-linked causes. The paper offers details about the chemistry of halitosis (bad breath) and of odorous urine as well as of odorant reproductive fluids. Much of the paper is also devoted to sweat and skin. The authors conclude that “evidence-based guidelines for management of body malodor are lacking, and no universal treatment exists. However, the alleviation of the symptoms may be achieved by controlling the diet and physical elimination of bacteria and/or accumulated odorants.”

References

1. Lam TH, Verzotto D, Brahma P, Ng AHQ, Hu P, Schnell D, Tiesman J, Kong R, Ton TMU, Li J, Ong M, Lu Y, Swaile D, Liu P, Liu J, Nagarajan N. Understanding the microbial basis of body odor in pre-pubescent children and teenagers. Microbiome. 2018 Nov 29;6(1):213. doi: 10.1186/s40168-018-0588-z. PMID: 30497517; PMCID: PMC6267001.
2. Troccaz M, Gaïa N, Beccucci S, Schrenzel J, Cayeux I, Starkenmann C, Lazarevic V. Mapping axillary microbiota responsible for body odours using a culture-independent approach. Microbiome. 2015 Jan 24;3(1):3. doi: 10.1186/s40168-014-0064-3. PMID: 25653852; PMCID: PMC4316401.
3. Rudden M, Herman R, Rose M, Bawdon D, Cox DS, Dodson E, Holden MTG, Wilkinson AJ, James AG, Thomas GH. The molecular basis of thioalcohol production in human body odour. Sci Rep. 2020 Jul 27;10(1):12500. doi: 10.1038/s41598-020-68860-z. PMID: 32719469; PMCID: PMC7385124.
4. Mogilnicka I, Bogucki P, Ufnal M. Microbiota and Malodor-Etiology and Management. Int J Mol Sci. 2020 Apr 20;21(8):2886. doi: 10.3390/ijms21082886. PMID: 32326126; PMCID: PMC7215946.

Paolo Giacomoni, PhD

Insight Analysis Consulting

paologiac@gmail.com
516-769-6904

Paolo Giacomoni acts as an independent consultant to the skin care industry. He served as Executive Director of Research at Estée Lauder and was Head of the Department of Biology with L’Oréal. He has built a record of achievements through research on DNA damage and metabolic impairment induced by UV radiation as well as on the positive effects of vitamins and antioxidants. He has authored more than 100 peer-reviewed publications and has more than 20 patents. He is presently Head of R&D with L.RAPHAEL—The science of beauty—Geneva, Switzerland .