Re: do some people's hair(on head) grow faster than others? if so, why ?

Hmm.  I'm kind of short on authoritative references here, but from anecdotal 
evidence i would say that some people definitely grow hair faster than 
others.  My wife and I recently had a baby, and the mother's hair growth 
definitely increases during pregnancy, and slows afterward.  On the other 
hand, I have heard that malnutrition can lead to slow hair growth and even 
hair loss.  Hormonal changes definitely increase the growth rate and 
character of pubic hair, as well as facial hair in males, but I'm not 
certain whether puberty has any effect on scalp hair.  I did have one friend 
who went from straight to dramatically curly around fifteen, but he's pretty 
much the exception that proves the rule.  

I can definitely say that there isn't much you can do to change a given 
person's hair growth rate.  Hair grows in a cycle: during anagen the hair 
grows, and then in telogen growth ceases and the hair falls out.  For 
example, eyebrow hair follicles have a relatively short anagen period in 
everyone except my father in law, growing to a normal length of about 10 mm 
before falling out.  Follicles on the scalp normally have a much longer 
anagen phase, allowing growth to lengths of over a meter.  Recent "hair 
regrowth" drugs such as Rogaine and Propecia prolong anagen, but do not 
increase the rate of growth of the hair during anagen.  So at this time 
there isn't much that can be done to either increase or decrease the rate of 
hair growth.

As for the influence of genetics on hair growth, I am sure there is an 
effect but I'm not aware of any efforts to study it in normal individuals.  
Most hair growth research is currently conducted on androgenetic alopecia, 
more commonly known as male pattern baldness.  As mentioned above, 
androgenetic alopecia is not a question of the rate of growth of a given 
hair, but of the rate of the anagen/telogen cycle in each follicle. 

Finally, I don't really know how the rate of facial hair growth correlates 
to the rate of scalp hair growth.  I am aware of friends who develop five 
o'clock shadow well before five o'clock, while it takes me two or three 
days, but I suspect that it is more a matter of hair pigmentation than rate 
of growth.

	I'm sorry I can't be more authoritative on your topic.  An excellent 
web reference for the basic biology of hair is:
 http://www.keratin.com/aa/aaindex.shtml  

The scientific evidence they cite holds up well against what I already knew 
of hair biology, so I'd say they're fairly trustworthy.  You could also 
check out propecia.com and rogaine.com, but these sites are definitely more 
interested in selling you product than educating you.

	Chris Carlson
	peterpan47@earthlink.net