Azelaic acid is a well-known inhibitor for 5a-reductase and is therefore able to inhibit the conversion of testosterone into dihydrotestosterone. Due to the relative absence of dihydrotestosterone regression of the hair follicle will take place (the catagen stage), and subsequently hair generation will take place (the anagen stage).
Azelaic acid is proven to inhibit the 5a-reductase which is the enzyme that will convert testosterone to 5a-dihydrotestosterone which is the major cause of hair loss. Basically if the dihydrotestosterone is eliminated hair loss will be stopped or minimized. Products containing Azelaic Acid, vitamin B6, and Pyridoxine hydrochloride, in low doses show a 90% reduction in this 5a-reductase activity leading to reduction of hair loss and/or many times regrowth.