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Androgenetic Alopecia Overview:

In androgenetic alopecia, larger terminal hair follicles are replaced by smaller vellus hairs.

Primary Affected Scalp Regions:

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• Temples

• Vertex scalp

• Mid-frontal scalp

 

Within these regions, hair loss patterns emerge:

 

• Bitemporal Loss: Begins at the front hairline and progresses backward.

• Vertex Scalp Loss: Starts centrally and spreads outward in a circular manner.

• Mid-Frontal Scalp: Hair thinning appears in a pattern similar to a Christmas tree.

 

Note: The severity of hair loss can vary across these zones. For example, some men might experience more pronounced baldness at the front compared to the crown.

 

Key Features of Male Androgenetic Alopecia (MAA):

• Shift in hair cycle dynamics.

• Shrinking of hair follicles.

• Inflammatory responses.

 

Hair Cycle Dynamics:

Hair Growth Cycle: Hair grows, rests, and sheds in a recurring cycle:

Growth (Anagen): Lasts 3-5 years, primarily dictating the hair's final length.

Involution (Catagen): A short phase lasting a few weeks.

Rest (Telogen): Approximately a 3-month phase.

Regeneration: New hair begins to form in the early stages of the anagen phase.

 

Hair Cycle Traits:

• Hair growth remains consistent at about 1 cm/month.

• Humans exhibit varying hair cycles across different body regions.

• Numerous molecular signals, like growth factors and cytokines, play a role in guiding the hair cycle.

 

Molecular Influences on Hair Growth:

Promoters of the anagen phase: IGF-1, hepatocyte growth factor, and more.

Facilitators of the catagen onset: TGF-beta, interleukin 1-alpha, among others.

 

Androgenetic Alopecia and the Hair Cycle:

 

• The growth phase shortens with each cycle.

• Longer rest periods lead to noticeable hair shedding during combing or washing.

• Over time, hair might not grow long enough to even emerge from the skin.

• An extended latent phase, known as kenogen, results in more vacant follicles, advancing baldness.

 

MAA Hair Traits:

• Lighter, thinner hairs replace thicker, coloured strands.

• Androgens seem to diminish hair colour in alopecia by restraining stem cell factor (SCF) in dermal papilla, crucial for melanocyte migration and colouring.

• For an in-depth look at hair growth and loss, seek advice from dermatological studies or professionals.al