Androgenetic alopecia (AGA) or hereditary hair thinning is the most common form of hair loss. When it affects women, it is called female pattern alopecia or female pattern baldness. This condition is genetically inherited and can come from the mother’s or father’s side, or both sides, of the family.
The term “androgenetic” comes from androgen hormones that are responsible for causing the hair loss in genetically susceptible men and women. Androgens have other important functions in both males and females especially in normal male sexual development before birth and during puberty.
In susceptible hair follicles, an androgen – dihydrotestosterone (DHT) -binds to the androgen receptor and this hormone-receptor complex activates the genes responsible for the gradual transformation of large terminal follicles to miniaturized follicles. Increased levels of androgens in hair follicles can lead to a shorter cycle of hair growth and the growth of shorter and thinner strands of hair. Additionally, there is a delay in the growth of new hair to replace strands that are shed.
Both women and men with AGA have higher levels of 5 reductase and androgen receptor in frontal hair follicles compared to occipital follicles. At the same time, young women have much higher levels of cytochrome p-450 aromatase in frontal follicles than men who have minimal aromatase, and women have even higher aromatase levels in occipital follicles. The actions of these two enzymes play a major role in causing diffuse and patterned hair loss.
