Perspiration 

We have approximately 1.6 – 4 million sweat glands dispersed all over
the body. The density is higher under the arms, in the palms of the hands
and soles of the feet than other places on the body.
 
Perspiration is a watery solution, in itself completely odourless. Despite
this we often experience that perspiration has an unpleasant smell.
The odour is caused by bacteria on the surface of the skin when they
break down (metabolising) the components of the perspiration.
 
We have two types of sweat glands: the eccrine sweat glands which
are particulary found on the palms of the hands and soles of the feet
and the apocrine sweat glands, which are mostly present in the armpits.

Did you know?
30% of the broad population on a weekly basis sweat to an extent that is it is of discomfort to them. Among these, corrective behaviour actions are common e.g. carrying an antiperspirant with them throughout the day and avoid lifting their arms and not wearing certain types of fabrics.

Source: IHS (USA) sweat survey 2008 and MyResearch sweat survey 2009 (Germany and the UK).