Sweating

Sweating is a normal human response to heat, embarrassment and fear.  There are millions of sweat glands in the skin that produce sweat.  The sweat glands are coiled tubes that have only one opening, that out onto the surface.  The cells that make up the wall produce the sweat.

Sweat is namely water but also has some simple substances in it such as sodium, chloride and urea.  This why sweat tastes salty if licked.

The primary reason to sweat is to lose heat.  When water evaporates, it takes energy from the surface it is on to do so.  Therefore, when you sweat onto the surface of the skin, and the sweat evaporates, it takes heat away from the body.  It is a very efficient way of losing heat.

In humans, this is one of the major ways we control our temperature.  If we are cold, we move to warmer areas, shiver or wear more clothes.  If we are hot, we try to move to cooler areas, take off clothes and sweat. 

Animals smaller in size than humans do not have sweat glands.  They have smaller body masses and therefore do not generate so much heat.  If they do get hot, they have other mechanisms for losing heat.  For example, dogs that get hot, lose heat by panting.  They hang their tongues out which have saliva on and then breathe hard across these to force the saliva to evaporate.  This cools the tongue down and the blood that is flowing through the tongue.  As such, this helps to cool the body down.

Animals bigger than humans have very big body masses and as such produce an awful lot of heat.  Therefore, these larger animals all need to sweat to lose heat, as well as having other behavioural habits which also help to keep them cooler.

So basically, sweating is a normal function.  Although sometimes it can be embarrassing, in the vast majority of people, embarrassing effects can be controlled by simple measures such as not over-exerting in public, wearing cool clothes that do not show sweat marks, and using anti-perspirants.

Excessive sweating is called hyperhidrosis.  There is no strict definition for excessive sweating.  However, some people clearly have sweat rolling off their hands or faces in temperatures and situations where normal people do not and this is clearly hyperhidrosis.

Other people get damp patches beneath their arms or sometimes in the small of the back that shows through their clothes.  This might be hyperhidrosis or just heavy sweating.  Either way, it is embarrassing and can almost always be treated to the benefit of the patient.

Apart from the heat loss role of sweating, humans also sweat when they are stressed.  This stress might be embarrassment, or might be anger or fear.  All of these stresses cause us to produce adrenaline from our adrenal glands, giving us the “fight or flight” response.  Basically the fight or flight response gets the body ready to either fight off threat or to run away from the threat.  One part of this response is the massive release of adrenaline and noradrenaline from glands called the adrenal glands.  These hormones go round the bloodstream getting the muscles and blood vessels ready to either fight or run away.

At the same time, the nervous system also activates to help this.  A special part of the nervous system, called the sympathetic nervous system, also fires off having many effects around the body.  Most of these effects are to prepare the muscles of fight or flight.  However, one of the side-effects is to cause sweating from the sweat glands.  This is because the sympathetic nerves control the sweat glands.