A 39 year old female writes to inquire as to why she is losing her hair.  Here's my response:

 Your e-mail was forwarded to my attention so I hope you do not mind if I reply personally.  I should preface my comments by noting that I am a Ph.D. research scientist, NOT an M.D. clinician.  This means that any thoughts I offer in this regard should not be construed as medical advice.  As long as we both appreciate the limitations of what I've just conveyed, here are my thoughts.

Statistically speaking, the most common reason why a 39 year old healthy woman loses her hair is due to androgenetic alopecia (AGA), also known as common pattern hair loss.  This is not to say that it is an absolute certainty that you are suffering from AGA and not another kind of loss.  Merely, I point out that the statistical odds favor AGA over the less common disorders.

 In men, pattern hair loss happens earlier in life, often with signs and symptoms manifesting by age 21 to 24.  In women, the disorder tends to occur later at around age 40 or 45.  It is thought that hormonal changes linked to menopause may contribute to the onset and progression of AGA.  Female hair loss is characterized by general thinning rather than bi-temporal recession and a mid vertex bald spot such as found in males.  The feminine hair line is almost always preserved, but density is greatly diminished throughout. 

Biochemically as well as genetically, the triggers that cause hair to thin in women are remarkably congruent with those found in men.  In essence, it is the same disease process, manifesting a bit differently depending on gender.

The spectrum of treatment choices available for women offer some options (e.g. spironolactone) unavailable to males, but there are also treatments for men (e.g. finasteride) that are not indicated for women.  Ultimately, your best next step should be referral to a physician with experience in treating hair loss in women.  This is a useful and quite necessary step as it will clarify your situation and allow you to understand the best possible treatment options available for your situation. 

I understand that I've not really given you the answers you're looking for.  But I hope I've at least given you a framework that you can use to approach the problem systematically and logically.  Let me know if you've any further questions.  I'll do my best to help with any female hair loss questions.