AGA (male pattern baldness): How hair begins to fall out

1. M-shaped hair removal

The most common early stage of AGA is “M-shaped” thinning hair, in which the hair gradually recedes from the hairline of the forehead.

• The hair thins from both sides of the forehead (temple area) and gradually recedes. The hairline in the center often remains, resulting in an M-shaped appearance.
• As the hairline recedes, the forehead appears wider. At this stage, it may not be noticeable because there is still volume in the hair as a whole.

2. o-shaped hair loss on the top of the head

Another typical type of hair loss is “O-shaped” hair loss, in which the hair thins from the top of the head (the whirlpool area).

• The hair on the top of the head becomes thinner and the hair density gradually decreases. Hair thinning begins around the whirlpool and progresses to an O-shaped thinning of the hair.
• This shedding may be difficult for the individual to notice, but is often noticeable when viewed from above.

3. progression of M- and O-shape

As AGA progresses, the M-shape and O-shape develop respectively, eventually connecting the top of the head and the hairline, resulting in extensive thinning of the hair.

• Fusion of frontal and parietal areas: As M-shaped and O-shaped hair loss progresses, the parietal and forehead hair loss areas are connected, forming a large thinning area from the frontal to the parietal area.
• U-shaped thinning: Eventually, it is common for hair to remain only on the back and sides of the head, resulting in a U-shaped thinning ( also known as crowning ).This condition is typical of the so-called “bald head.

4. changes in hair fineness and weakness

Hair loss due to AGA is not simply the loss of hair; it is a process of thinning and weakening of the hair.

• Softening of hair: As AGA progresses, hair becomes softer and finer. This is because the hair cycle is shortened and hair does not grow fully. As the hair that falls out becomes thinner, the scalp begins to become more exposed.
• Shortened growth phase: Normally, hair has a 2-6 year growth phase, but as AGA progresses, this growth phase is shortened and hair falls out without sufficient growth.

5. classification of AGA progression patterns (Norwood classification)

The progression of AGA is commonly classified into stages according to a criterion called the Norwood Classification. This divides the progression of AGA into seven stages.

• Norwood Type I: Early stage with little or no hairline recession or thinning at the crown of the head.
• Norwood Type II: Stage in which the hairline begins to recede in an M-shape.
• Norwood Type III: The stage when the M-shaped recession becomes clearly noticeable. The top of the head may also thin.
• Norwood Type IV: A stage in which recession of the M-shaped hairline and thinning of the hair at the crown of the head progresses further, with hair remaining between the crown and the hairline.
• Norwood V: A stage in which the hair on the top of the head and at the hairline begins to connect, resulting in extensive thinning of the hair.
• Norwood Type VI: A stage in which the top of the head and the hairline are completely connected, leaving only hair on the back and sides of the head.
• Norwood Type VII: Most advanced condition, with only a few hairs remaining on the back and sides of the head.

6. if the progression of AGA is left untreated

AGA, if left unchecked in its progression, often leads to gradual thinning of the hair and eventually to extensive hair loss. By starting treatment as soon as one becomes aware of the disease, it is possible to control the progression and promote hair regrowth.

summary

Hair loss in AGA (male pattern baldness) is characterized by a receding M-shaped hairline and O-shaped thinning at the crown of the head. These patterns progress in stages, and if left untreated, extensive hair loss and eventually U-shaped thinning are common. Early initiation of treatment can slow the progression and improve thinning hair.

記事の監修者

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岡 博史 先生

CAPラボディレクター

慶應義塾大学 医学部 卒業

医学博士

医師