What is Androgenetic Alopecia?
Androgenetic Alopecia, in laymen’s terms is called Male Pattern Baldness or hair loss. This is the most common type of hair loss in men. This process is mediated by the Genetic Code. This is a tendency that we inherit from our parents, from both sides and from multiple generations back. It’s poly-genetic and a complex pattern of inheritance, so you can’t say it comes from your dad’s side or mom’s side exclusively.
Basically we divide the hair follicles into 3 categories (Refer to Image 1):
- Terminal hairs (the hairs visible on your scalp)
- 60-84 microns in diameter
- Miniaturized hairs
- 30-60 microns in diameter
- Vellus hairs
- Less than 30 microns in diameter
- Examples of Vellus hairs are the hairs on the back of your hands. You will notice a lot of very small hair follicles, and you almost need a magnifying glass to see them.
Miniaturized and Vellus hairs will not make a big impact on your scalp. Even if your scalp was covered with a million of them, you will almost not see the hair. You need terminal hairs with a caliber of 60-84 microns to have an aesthetic impact.
Causes of Androgenetic Alopecia
There is a process called miniaturization where your hair follicles get smaller in caliber and length over time and that is the effect of Androgenetic Alopecia.
How does this happen? The male hormone testosterone is converted by the enzyme 5 Alpha Reductase, and the male hormones have an affinity to bind with androgen receptors which are located on some of the hair follicles.
Some people have a lot of these receptors and at a young age they will look like the graphic VII (see Norwood Scale below) although they are only in their early 20’s. Other people have very few of these receptors and at 80 years of age, they will still have a full head of hair similar to graphic II (See Norwood Scale below). Most people are somewhere in-between these extremes such as seen on a natural bell shaped curve (see Normal Curve below). Read more on the stages of male pattern baldness.
On the Normal Curve image above you will see that approximately 64% of males will be in the light grey area, 15% of males will be in the darker areas to the right and left of the center area of the Bell Shaped Curve. Then the dark small areas on the far left and far right represent the small percentage of men who lose hair in their early 20’s and those who don’t lose hair even in their 80’s and older.
When male hormones bind with the androgen receptors there is a reaction in the nucleus of the cell that triggers the miniaturization process. This diminishes the energy supply (ATP) to the cells and the oxygen gradient drops. Over time the follicle does not get enough nutrients to grow becoming smaller and smaller. This process is called miniaturization. The follicles lose their calibre and become shorter. This is what causes the appearance of hair loss. It is actually loss of hair volume and as a consequence over time the scalp becomes more visible.
The caliber is the critical factor. If we look at a hair shaft, the hair shaft is in the shape of a cylinder. If you want to calculate the volume of a cylinder, you calculate the surface of two circles (use Pi x radius squared) on either end of the cylinder. In the case of a hair shaft cylinder, it is will be 2 x Pi x Radius (square) x the height or length. That is how you calculate the volume of the hair shaft cylinder as seen on the Hairshaft Calibre image below.
Now you need to calculate the total volume of all the hair shafts on your scalp (the hair mass index or the cross sectional trichometry). The bigger the volume of hair, the bigger the chances are that its going to shut out the reflection of light from the scalp and look like a full head of hair. The reflection of light from the scalp through thin hair creates the perception of hair loss. Its as simple as that from a pure physics point of view. More about the structure of hair.
See below example to demonstrate the importance of hair shaft caliber. If for instance we take the hair shaft radius at 10 microns. Because the Radius is squared in the hair shaft cylinder volume calculation, the radius is the critical factor. See different radius sizes squared and the effect on caliber below:
- 8 microns x 8 microns = 64 micron caliber
- 9 microns x 9 microns = 81 micron caliber
- 10 microns x 10 microns = 100 micron caliber
- 11 microns x 11 microns = 121 micron caliber
- 12 microns x 12 microns = 144 micron caliber
From this example it is clear that a small change in hair follicle radius, creates a large change in caliber. We have calculated in hair restoration that if the caliber of the hair shaft changes with more than 10 microns, there is a 36% volume effect. The average persons’ hair shaft caliber is around 68-70 microns. If for example the caliber goes down to 58 microns, then literally 36% of the persons’ hair is not visible, although all the hair shafts are still there. This happens because the total hair shaft volume has gone down. So this person has lost hair volume.
This concept is easier to convey if you look at it from a two dimensional view (see Types of Hair image above). Let us say this picture demonstrates 3 different surfaces of the scalp.
In the top section there is one thin hair shaft crossing from side to side and a number of smaller short hair shafts. A relatively straight hair shaft or straight and short hair shaft does not provide much scalp surface cover. You will need many of those types of hair shafts to create any density at all and it will essentially be ineffective in the end.
The second section above shows a single hair with a curl-and-a-wave. This hair covers more surface area than the single straight hair in the top section. So if we draw more curved hair lines, we will need to draw less of these types of hair lines to cover the surface when compared to the number of straight hair lines required to achieve the same density. This is because curved hairs cover more surface area than straight hairs. Therefore, a curl-and-a-wave is worth more in hair transplantation than a relatively straight hair.
The third (bottom) example above shows a coarse hair with good caliber and it also has a curl-and-a-wave. This covers even more scalp surface area. So we only need a few of these type of hairs to cover the sectional area in order to shut out the reflection of light.
This is one of the most important principles in hair transplant surgery, whereby we create the illusion of hair density. What you want is to maximize the caliber and keep the hair shaft relatively long and if there is a curl-and-a-wave it works even better to shut out the reflection of light from the surface of the scalp. Find out more about maintaining and maximizing hair density: