In short
Sweat is odourless. A few bacterial species living on the skin break down odourless molecules in underarm secretions; this is how sharp-smelling molecules are released.
Fresh sweat doesn't smell
This was first shown in 1953: fresh underarm sweat is odourless. In 2004, Swiss researchers collected 500 ml of sterile underarm sweat from 30 volunteers. The sweat was odourless. When it was left to stand with bacteria, the familiar smell of sweat developed.
Who makes the smell?
Underarm secretions contain odourless precursor molecules. When certain bacteria break them down, two kinds of odour appear: sour, cheesy acids and oniony sulphur-containing molecules. Our noses pick up the sulphur ones even in very small amounts.
Not every bacterium in the armpit produces odour. The enzyme that releases the oniony smell is found in only one group of staphylococci. S. epidermidis, one of the most common species in the armpit, produces little odour.
Why does everyone smell different?
The bacterial community in the armpit is unique to each person and changes little over time. Secretions differ too: men have three times as much of the raw material for acid odour as women, while in women the sulphurous odour stands out.
What does deodorant do?
Deodorants and antiperspirants change the bacterial community in the armpit. In one study, bacterial numbers rose in people who stopped using antiperspirant, then dropped sharply when they started again.
Scientists are working on the idea of reducing odour not by killing all bacteria, but by supporting the ones that don't produce odour. This idea is still at the research stage.
In everyday life
Regular showering removes both the raw material for odour and the bacteria that produce it from your skin. After exercise, wash your armpits, chest and back with a little extra care. Prebiotic Shower Gel is formulated to help against sweat odour and is free from harsh sulphates.
Sources
- Shelley WB, Hurley HJ, Nichols AC (1953). Axillary odor; experimental study of the role of bacteria, apocrine sweat, and deodorants. AMA Archives of Dermatology and Syphilology 68(4):430–446. doi:10.1001/archderm.1953.01540100070012
- Troccaz M et al. (2004). 3-Methyl-3-sulfanylhexan-1-ol as a Major Descriptor for the Human Axilla-Sweat Odour Profile. Chemistry & Biodiversity 1(7):1022–1035. doi:10.1002/cbdv.200490077
- Natsch A et al. (2003). A Specific Bacterial Aminoacylase Cleaves Odorant Precursors Secreted in the Human Axilla. Journal of Biological Chemistry 278(8):5718–5727. doi:10.1074/jbc.M210142200
- Natsch A, Schmid J, Flachsmann F (2004). Identification of Odoriferous Sulfanylalkanols in Human Axilla Secretions. Chemistry & Biodiversity 1(7):1058–1072. doi:10.1002/cbdv.200490079
- Bawdon D et al. (2015). Identification of axillary Staphylococcus sp. involved in the production of the malodorous thioalcohol 3-methyl-3-sufanylhexan-1-ol. FEMS Microbiology Letters 362(16):fnv111. doi:10.1093/femsle/fnv111
- Rudden M et al. (2020). The molecular basis of thioalcohol production in human body odour. Scientific Reports 10:12500. doi:10.1038/s41598-020-68860-z
- Callewaert C et al. (2013). Characterization of Staphylococcus and Corynebacterium Clusters in the Human Axillary Region. PLoS ONE 8(8):e70538. doi:10.1371/journal.pone.0070538
- Troccaz M et al. (2009). Gender-Specific Differences between the Concentrations of Nonvolatile Odor Precursors in Axillary Secretions. Chemical Senses 34(3):203–210. doi:10.1093/chemse/bjn076
- Urban J et al. (2016). The effect of habitual and experimental antiperspirant and deodorant product use on the armpit microbiome. PeerJ 4:e1605. doi:10.7717/peerj.1605
- Callewaert C, Lambert J, Van de Wiele T (2017). Towards a bacterial treatment for armpit malodour. Experimental Dermatology 26(5):388–391. doi:10.1111/exd.13259
These studies were not carried out with EcoProbiotic products.