I usually don't comment on animal medical 
problems without seeing the pet(its too easy to 
misdiagnose on verbal descriptions alone), but 
after reading the other comments I need to put in 
my two cents.  Most animals I see that are 
licking out their hair are doing so because of 
allergies and not stress.  Other possibilities 
include scabies, ringworm and bacterial 
infections. Since some of these conditions are 
contageous to people, testing or at least a 
physical is very important.  The most common 
allergies I see here in California (I don't now 
where you are located)are to fleas and/or pollens 
and therefore you will often notice a seasonal 
pattern.  It will vary a bit though on your 
region. Treatment varies depending on the 
specific problem but even allergic conditions can 
be controlled to some degree. 

Sorry, I promise no more off the topic messages.