Re: What causes hair to turn gray?

  Kelly,
    Hair color is produced by a variety of human pigments, most notably, 
melanin.  Melanin is produced by melanocytes that are found within the 
layers of the hair follicle.  When hair is produced by the reproduction of 
the epithelial cells comprising the follicle, newly produced melanin 
accumulates in the cells and colors the hair itself as it emerges from the 
follicle.  
    Those people with gray hair make little or no melanin and, therefore, the 
hair is virtually transparent and we see the color of the dead cells comprising 
the hair.  There are several reasons for gray hair and these vary by one's 
age.  A big one is heredity.  If you have genes from your family that code for 
"turning off" the metabolism of the melanocytes at an early age, you will go 
gray at a rather young age.  If your genes code for gray hair at a later time, 
you will become gray as you get older. This may also be done by less blood 
supply to the follicles.  
    The other big reason for graying hair is the environment.  A recent study 
indicates that smokers are 4 times more likely to become prematurely gray (or 
bald).  The mechanism is not clear but may have to do with vessel constriction 
caused from the chemical (such as nicotine) absorption . In youngters, vitamin 
B-12 deficiency, thyroid imbalance, anemia or viruses can cause gray hair to 
appear as well.  There is a  phenomenon of "going gray" due to a shock or 
fright but is not well documented and is hard to explain physiologically.

    I hope this answers your question.