James Hamilton introduced a scale to measure the stages of male pattern baldness in the 1950s. Dr. O’Tar Norwood then significantly improved this scale in the 1970s.
The Norwood scale defines seven stages of baldness, with specific models for each type of baldness. Each stage has a normal pattern and a class A pattern.
The normal pattern tends to start with a bald spot on the top of the head. Class A balding has a different progression, wherein the hairline recedes from the front to the back instead.
Stage 1 of the Norwood scale is the control stage. People in stage 1 of male pattern baldness still have a full head of hair, with little to no signs of baldness or a receding hairline.
In stage 2, there is only slight evidence of a receding hair line, generally around the temples.
Generally, hair loss starts to become noticeable during stage 3. The hairline typically pulls backward from the temples, giving it a curved “M” shape when viewed from above.
In the class A version of the scale, or stage 3A, the dips in the hairline may be slightly less defined.
Stage 3 vertex
In terms of the receding hairline, stage 3 vertex balding is a less drastic version of stage 3.
However, people experiencing stage 3 vertex balding will also begin losing hair on the crown of their head. This often starts as one small bald spot.
By stage 4, there is significant hair loss. The hairline recedes farther and may start to resemble a “U” shape when viewed from above.
The bald spot on the crown is larger, but there is still a strip of hair between the bald spot and the receding hairline.
In stage 4A, a person will not experience a bald spot on the back of their head, but they will instead lose the dips in their hairline and have a deeper “U” shape when viewed from above.
Stage 5 shows similar progression to stage 4 but is more severe. There is still a small section of hair between the receding hairline and the balding crown. However, this strip of hair is much thinner than in the previous stage.
In stage 5A, the hairline continues to progress toward the back of the head.
Someone with stage 6 baldness is now mostly bald on the front and top of their head. The two bald areas now join together, and there is no strip or patch of hair between them.
There may still be hair on the sides of the head, but the crown and front of the head are now mostly bald.
By stage 7, the baldness also begins to affect the sides of the head, until only a thin ring of hair encircles the outside of the head.
The hairs that grow are likely to be very thin and weak.
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