What is the chemistry behind smell of human perspiration(sweat)?
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)


Source: ncbi and chemistry.about