A consumer wishing to understand the actual triggers of hair loss inquires. 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.

To begin with, three things need to occur in order for one to lose hair due to common pattern hair loss(by far the most prevalent kind). 

1.  One needs to have the genetic susceptibility.  This means that a person needs to inherit genes that render one susceptible to the triggers that result in hair loss.

2.  One needs to reach a certain age.  Commonly, nine year old children do not experience pattern hair loss. 

3.  And finally, one needs to have the circulating hormones that precipitate pattern hair loss. 

Each of these three factors, genetics, chronobiology, and biochemistry are exquisitely complex.  For example, it is widely believed that the genetics of pattern hair loss are associated with a fairly large number of genes interacting in intricate orchestration.  This is one reason why there are so many degrees and variations of pattern hair loss within the general population.

Further, although you correctly point out that testosterone metabolizes dihydrotestosterone as its most active metabolite, in and of itself, this metabolism does not necessarily precipitate pattern hair loss.