What is the chemistry behind the bad smell of human perspiration? also what is its composition?
Why does sweat smell?!
Sweat released from sweat glands odourless. Bad smell of sweat is due to certain bacteria on your skin mix with sweat(That is why sweat smell bad after sometime) and also due to certain hormones released during puberty.
I have tried my best to keep this part chemistry point of view(Actually this belongs to biology).
Chemical composition of sweat
The main reason people perspire is so evaporation of water can cool the body. Thus water is main component.
The chemical composition of perspiration varies between individuals and also depends on what they have been eating and drinking, why they are sweating, how long they have been perspiring and several other factors.
On average, the mineral composition is:
- sodium (0.9 gram/liter)
- potassium (0.2 g/l)
- calcium (0.015 g/l)
- magnesium (0.0013 g/l)
Trace metals that the body excretes in sweat include:
- zinc (0.4 milligrams/liter)
- copper (0.3–0.8 mg/l)
- iron (1 mg/l)
- chromium (0.1 mg/l)
- nickel (0.05 mg/l)
- lead (0.05 mg/l)
In addition to simpler lower carboxylic acids contributing rather to socks smell (see Q: Why do socks stink?), some notable representatives contributing to the human axilliary (armpit) odor are
- (I) 3-hydroxy-3-methylhexanoic acid,
- (II) (2E)-3-methylhex-2-enoic acid,
I enantiomers (S)-I and (R)-I occur in approx. ratio 2:1, where (S)-I detection threshold by human smell sense was measured 0.08 ng/L air, cumin like smell; (R)-I detection threshold 0.2 ng/L air, weak animalic odor.
- (III) 3-sulfanylhexan-1-ol,
- (IV) 3-methyl-3-sulfanylhexan-1-ol,
- (V) 1-methoxyhexane-3-thiol.
These can be smelled in much lower concentrations, and stereochemistry matters – lowest measured (S)-V 4×10−5 ng/L, compared to (R)-V 1.09×10−3 ng/L.
These are real human products unlike bacterial decomposition products above. Their role is not completely understood. VII is oxidation product of VI and has stronger odor. It is claimed some people cannot smell it because of mutation in one of olfactory receptors gene. It is sometimes also claimed, that there are sexual pheromones detectable by (in humans controversial) vomeronasal organ. They appear not only in humans, but also other animals like pigs.