MadSci Network: Environment

Re: How does a low relative humidity affect our human bodies?

Date: Thu Jan 29 16:44:10 2004
Posted By: Peter Gaul, Grad student, OHS & Environmental Management, company - non educational
Area of science: Environment
ID: 1075370468.En

Hi Marsha,

Humans, and every other organism, survive within a species specific 
range of environmental tolerances.  Survival tolerances exist for all 
environmental conditions including pH, temperature, noise, U.V. radiation 
and obviously humidity.

In a simple example this is why you don't see polar bears in the tropics 
nor cactus in a rain forest.  It is also why it is so hard for fish 
lovers to set up a marine fish tank - the bandwidth of tolerances for 
these fish are so small.

As humans we stretch the survival tolerance.  Through tools, clothing 
and invention we manage to survive in the hotest deserts as well as at 
the poles.  We thrive in everything in between.

Unfortunately these inventions include crazy 6" high heels for women, 
chemicals on our skin and in our diet, not to mention artificial lighting 
and air conditioning in our workplaces.  None of which are really geared 
toward our natural tolerances or physical design.

In answering your question, there are several affects of humidity on us 
as humans.  An example is people suffering from heat stress in high 
temperature, high humidity, manual labour.  One of our most effective 
natural cooling systems is the use of sweat which is released onto our 
skin and evaporates away taking with it heat energy.  High humidity 
reduces this evaporation and therefore interferes with our cooling, 
potentially resulting in debiliating sickness and even death.

As far as indoor requirements I checked the Australian Standard 1668:2002 
(The use of ventilation and airconditioning in buildings) which states 
that it does not prescribe humidity requirements for buildings - no luck 

However, according to air purifier suppliers 
( and some unknown authority ASHRAE 
(possibly American - I am Australian) humidity under 25% "is associated 
with increased discomfort and drying of the mucous membranes and skin" 
while "high humidity can result (in)... the ... development of mold and 
fungi along with the increase of dust mite propagation".  Seems both high and 
low humidity could cause breathing problems in sensitive people.

Being an undergrad I suggest you take the opportunity to practice your 
skills in ensuring the validity of your sources and get onto the 
supplier's website and find out who ASHRAE are and, if they are a 
recognised expert body or government agency, check out a copy of their 

Good luck.


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