Androgenic Alopecia: Definition, Pathogenesis, Etiology, Manifestation, Frequency and Prevalence – Androgenetic alopecia is a hair disorder that is often found in both men and women. Androgenetic alopecia in males is often referred to as male pattern hair loss, an androgen dependent and genetically determined disorder.
While in women it is often called female pattern hair loss, but the role of androgens is less pronounced than in men.
The disorder is characterized by a progressive decrease in the length of the anagen phase, which is the hair growth phase.
On the other hand, there is an increase in the telogen phase, and miniaturization of hair follicles in the scalp area, which ends with the regression of the hair follicles.
Androgenic Alopecia Definition
Androgenic alopecia is a hair loss that is affected by a genetic condition that can affect both men and women. Men with this condition can start suffering hair loss in their teens or early 20s, whereas most women don’t start experiencing hair loss in their 40s or older.
Androgenetic alopecia pathogenesis
Normal hair growth cycle is divided into 3 phases, namely
- Anagen phase: matrix cells through mitosis form new cells pushing older cells upwards. This activity takes between 2-6 years.
- Catagen phase: the transition period preceded by thickening of connective tissue around the hair follicles. The middle part of the hair roots narrow and the bottom are widened and developed a stretch so that a club is formed. This transition period lasts 2-3 weeks.
- Telogen phase or rest period begins with shortening epithelial cells and small shoots that create new hair so that the hair club will be pushed out.
The length of anagen period is about 1000 days, while the telogen period is about 100 days, so the ratio of anagen and telogen hair ranges between 12:1. The number of hair follicles on the human head is about 100,000. The amount of hair loss per day is 100 strands. Androgen hormones can accelerate growth and thicken hair in beards, armpits, and suprapubic, but on the scalp, androgen hormones cause non-pigmented vellus hair. However, the difference in such effects is not yet clear.
Androgenetic alopecia etiology
The exact mechanism for the occurrence of androgenic alopecia is not yet clear, but it is suspected that alopecia is caused by stimulation of androgen hormones against hair follicles that have a predisposition. This predisposition is influenced by genetic factors and age-increasing factors.
Androgenetic alopecia manifestation
As for the clinical symptoms of androgenic alopecia according to Hamilton:
- Type I: hair is still full
- Type II: visible reduction in hair in both temporal parts
- Type III: Borderline
- Type IV: reduction of frontotemporal area hair
- Type V: type IV that becomes heavier
- Type VI: all abnormalities into one
- Type VII: widespread alopecia limited to rare hair bands
- Type VIII: frontotemporal alopecia into one vertex part.
Androgenetic alopecia frequency and prevalence
AGA in males appears on the entire population. The highest prevalence is in Caucasians, reaching about 80% in men over the age of 70. In the Asian population, its prevalence is reported to reach 60% in men over the age of 70 years. There is scant information that is reported about the frequency of baldness in African men. A previous study showed that baldness in African men was 4 times lower than that of Caucasian men. The frequency and severity of male AGA increase with the addition of age in all ethnic groups.
The specific signs of AGA are some of the recessions of the frontal and temporal hairlines that generally develop during adolescence. Progressions leading to deep frontal recessions and or vertex baldness can also occur in the near future after puberty, although in most men, the onset appears later. By the age of 70, about 50-60% of Caucasian men are generally bald.
Causes of Hair Loss In Men
As in men, the frequency of the population and severity of AGA increases with the addition of age in women. Two studies of Caucasian women in the UK and America showed a prevalence ratio of 3-6% in women under the age of 30, increasing to 29-42% in women aged 70 and over. This frequency is lower in Oriental women than in European descent. There are no data on the frequency of AGA in African women.