The Chemistry of Body Odours (Sweat, Halitosis, Flatulence & Cheesy Feet)

 Body odour has a strong genetic basis both in animals and humans, but it can be also strongly influenced by various diseases and psychological conditions.
Body odor is considered an unpleasant odor among many human cultures.

Body odour (BO), also spelled body odur, is present in animals (including humans), and its intensity can be influenced by many factors (behavioural patterns, survival strategies).

In the majority of cases, the cause of bad breath, or halitosis, is the product of bacteria in the mouth. These bacteria produce waste products, and it’s these chemical compounds that contribute towards halitosis.
The main offenders are volatile sulfur compounds, or VSCs; hydrogen sulfide has a smell of rotting eggs, methanethiol (also known as methyl mercaptan) has the odour of rotting cabbage, and dimethyl sulfide has similarly pleasant likeness to rotting cabbage, or garlic. At low levels, these compounds aren’t detected by the human nose, but it doesn’t take a great deal for them to become noticeable; 0.00047 parts per million is the threshold for the human nose being able to detect hydrogen sulfide, for instance.
As well as these main compounds, there are also some lesser compounds that can contribute, some of which are exacerbated by certain drinks or foodstuffs. For example:
  • The phenomenon of ‘coffee breath’ has been linked by the Journal of Breath Research with the compound 3-mercapto-3-methylbutylformate (the odour of which is brilliantly described here as ‘catty’).
  • Garlic breath is attributed to allyl methyl sulfide, a product of the breakdown of garlic, which unsurprisingly has an odour described as garlic-like.
  • Eating meat & fish can also lend your breath a formidable scent. The bacteria that produce VOCs thrive on proteins, and they can also produce other compounds, such as cadaverine and putrescine, associated with the smells of rotting corpses and rotting fish respectively.
Sulfur-containing organic compounds are again to blame for the variety of odours produced in the digestive system. The main sulfur-containing compound here is hydrogen sulfide, followed by methanethiol & dimethyl sulfide. 
An interesting observation of a study showed the difference between the farts of men and women. Men released more gas in one passage than women.

Underarm Odour
Your underarms are home to an estimated one million bacteria per square centimetre; these convert your otherwise odourless sweat into a variety of malodourous molecules.
Underarm odour actually introduces two organic compounds that don’t contain sulfur into the mix. 3-methyl-2-hexenoic acid is widely considered to be one of the main contributors to the human ‘sweaty’ aroma, which itself has an aroma delightfully described as ‘goat-like’. 3-hydroxy-3-methylhexanoic acid contributes a cumin-like scent, whilst 3-methyl-3-sulfanylhexan-1-ol (along with other sulfur-containing compounds) provides an onion note (it is in fact present in a 75:25 ratio of two enantiomers, the lesser of which has a fruitier aroma).

Foot Odour
Again, sweat is a major player in foot odour – however, as with underarm odour, it’s due to the fact that it provides a beneficial environment for bacteria to grow, and it’s the compounds that these bacteria produce that cause the perceived odour.
Methanethiol we’ve already come across at several points; two of the other main compounds contributing to ‘cheesy’ feet are propanoic acid & isovaleric acid. Propanoic acid is described as ‘pungent, sour and rancid’, whilst isovaleric acid attracts similar plaudits: ‘cheesy, rancid & fermented.’ The presence of isovaleric acid is actually the result of a bacteria also found in some strong cheeses.

  • Remedies to body odours vary and depend on individual preference. The most general is *frequent use of water*
  • Wash your mouth properly and regularly; drink water when you have to keep shut for a long time.
  • Dry your damp shoes.
  • Wash your clothes after use and dry properly and don't keep dirty under wears.
  • Get a spray or roll-on for your arm pits.
  • Do these now.
  • For those with Flatulence, controlled eating and use of laxatives will do.
CREDIT:  Diagnose me   CompoundChem


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