Today people run primarily for fitness—but primitive humans probably ran because they had to—in what's known as a fight or flight response:
With the fight or flight reaction, or in reactions where someone is extremely stimulated by central mechanism,
that is the hypothalamus of the brain—they will just begin to sweat and it doesn't matter what the temperature is outside.
When the adrenal gland is stimulated—… when you exercise—or from nerve activity like a date or job interview--
stress hormones such as cortisol and adrenaline are released into the body. When that happens your body's climate control mechanism revs into action and you sweat:
The chief reason for sweating is temperature regulation.
The average person has nearly 3 million sweat glands in their skin and they are commonly divided into two major types: Eccrine and Apocrine.
Eccrine glands are by far the more numerous of the two…
The eccrine glands are everywhere on the body.
The apocrine are oil glands that have a thicker, more potentially odoriferous sweating and they are mostly under the arms or in the groin area.
In addition to being thicker, sweat from apocrine glands sometimes has a yellowish color and often creates a smell when it comes into contact with bacteria on the skin.
That's one reason we apply deodorant and antiperspirants to our underarms and not to our entire body.
Sweat is odorless. It's the bacteria that break down the sweat that cause the problem that some people find offensive.
So, most of the time the forehead sweat evaporates and doesn't and bacteria don't get a chance to work on it, but in areas where there are folds of skin like under the arms or in the groin area,
then the bacteria is present and it breaks down the sweat and it causes an odor.
Humans have fewer of these smelly apocrine glands than nearly all other primates.
Because of the pungent smell, some believe they were designed to attract mates, mark territory or as part of an alarm reaction.
For modern humans, that "alarm reaction" may be your nose telling you to take a shower. For WebMD, I'm Damon Meharg.