What is the average pore size in the human skin?  Is there a range of
sizes?  If so, what is the range?

Hi saregamapa,

Well, this has been harder to find than I was expecting!  But here it
is...  the average (50 microns), along with various parts of the body.

Human Skin Pore Enlargement as a Result of Ultrasonic Treatment
"The structure of human skin is illustrated below. Typically the pore
diameter is only 50 microns..."
"The diameter of the skin was verified using a laser dermatology
scanner developed at Hershey Medical Center. The scanner confirmed the
expected starting average pore diameter at 50 microns (50 uM.)."
Skin Pore Value
"The sonicated skin was then laser measured and found to have
increased in size from an average 50 Um for the control untreated skin
sample to 92 Um for the arm skin sample average, 80.1 Um for the
abdominal skin sample, 65 Um for the back skin sample and 72 Um for
the thigh skin sample. These values are the averages of 10 samples
from each skin type."
"The author expected a different skin pore value for each skin site.
The abdominal values were higher than expected. The fatty tissue
present in these samples was expected to provide greater barrier
properties but the pore enlargement was very notable at this skin
site. The back skin was expected to be the lease responsive to
ultrasonic pore enlargement and this was borne out by the 65 Um for
the back skin pore diameter. However The author of this report
theorizes that there is an elastic property in several skin sites,
sufficient to enable the pores to be expanded ultrasonically. Beyond
the elastic limit the pores will not enlarge further."
http://www.encsys.com/articles/HumanSkinPoreEnlargementPaper.pdf

To put it in perspective, 1 micron = 1/1000 millimeter and the
diameter of human hair is 80 to 100 microns.

Additional Links of Interest:

Structure of Skin
"On the skin surface are the sweat gland pores (100-200/cm2) and the
openings of the sebaceous glands (50-100/cm2). Their secretions ensure
skin moisture and oiliness, and thus maintain the hydrolipid film. The
epidermis itself has no blood vessels, so the nutrients are supplied
through the fine blood vessels in the dermal papillae."
http://www.nmsl.chem.ccu.edu.tw/tea/SKIN_910721.htm

 The pore sets on top of the ridge.  It's physical purpose is to
provide a liquid cooling system for the exterior of the human body. 
Various types of waste is carried with the liquid that is expelled
through the pore during this cooling process.  The palmer surfaces,
palms and finger, and the plantar surfaces, soles of the feet and the
toes, have an average of 2700 pores per square inch of ridge friction
skin surface.  This compares to approximately 400 pores per square
inch of the balance of the body's skin surface.  These pores help
differentiate the ridges used in comparison, to ?incipient ridges?
that appear between the ridges used for identification."
http://www.scafo.org/library/110401.html 

The Skin You're In
http://www.subtleenergysolutions.com/newsletter-skin.html 

I was very happy to find this for you. If you have any questions,
please post a clarification request and wait for me to respond before
closing/rating my answer.

Thank you,
hummer

Google Search Terms Used:  human skin pores average pore size diameter microns

Thanks.