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 either the mother’s or father’s side 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 then the 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.
Did you know how do people inherit androgenetic alopecia?
The inheritance pattern of androgenetic alopecia is unclear yet because many genetic and environmental factors are likely to be involved. Although researchers are studying risk factors that may contribute to this condition, most of these factors remain unknown. This condition tends to cluster in families- therefore having a close relative with patterned hair loss appears to be a risk factor for developing the condition.
Onset may occur at any time after puberty and the majority of thinning occurs in the teens, 20s, and 30s. Women with hereditary thinning usually first notice a gradual thinning of their hair, mostly on the top of their heads, and their scalp becomes more visible. Over time, the hair on the sides may also become thinner. The patient may notice that her “ponytail” is much smaller in girth. This diffuse thinning of the scalp can vary in extent. Miniaturized hairs, the shorter and finer hairs of various lengths and diameters, are the hallmark of AGA and result from the shortening of anagen phase and reduction in matrix size. Increased spacing between hairs makes the central part appear wider over the frontal scalp compared to the occipital scalp.
Less commonly, hair density appears normal proximally, but the hair no longer grows to its previous length, resulting in wispy distal ends. In this case, the shortening of anagen progresses more rapidly than matrix reduction, therefore the hair is cut to shorter lengths in order to give a fuller appearance.
Androgenetic alopecia in women sometimes coexists with telogen effluvium- increased shedding following childbirth, major illness or other causes.