All men lose hair progressively as they age, although for some the loss is barely noticeable and for others it can be severe and occurs at a very young age with attendant distress and frustration. There are three areas of the scalp that preferentially lose hair:
- In the first the hair loss starts at the anterior hairline and moves backwards. It occurs at some point in children as they move from adolescence to adulthood and less than 5% of adult males retain a straight anterior hairline. It is usually a mild loss, although some men develop noticeable bitemporal recession.
- The second area is at the crown of the head and extends outward in all directions to produce a circular baldness.
- The third is the frontal midline, a common pattern in northern European men and a hallmark of hair loss in women as well.
A fascinating aspect of this is the way hair loss spreads through the hair follicles without skipping areas. The effect is that bitemporal recession produces a triangle of hair loss that slowly expands at each temple without damaging any of the follicles within the affected area. Moreover, there is no chemical that prevents hair loss.
Hair growth
Scalp hair is different from hair on other parts of the body. It grows in follicular units that produce tufts of 2 to 5 hairs that emerge from a single pore. Each follicular unit has a primary hair that is present at or shortly after birth and secondary hairs develop around two to three years of age, which is why infant hair is fine, light and soft, but becomes coarse over time.
Androgenic alopecia
When androgenetic alopecia first begins, it preferentially reduces the secondary hair, so that the follicular units in the affected scalp produce only a terminal hair instead of a tuft of hair. On the other hand, the total hair volume can be reduced by 50% without any visible bald spots.
Women tend to notice that the thickness of their hair decreases or that hair loss increases. In contrast, in the case of men, having shorter hair and sometimes being less observant they may not notice hair loss until actual baldness has developed.
The factors controlling hair loss progression patterns appear to be hereditary, as identical twins generally lose their hair at the same age, the same rate and in the same pattern. Genetic and epigenetic factors appear to be involved in this factor.
Uneven baldness and methods to combat it
The flip side of having regions of the scalp that lose hair is that there are also regions that do not lose hair, such as the back of the head (or occipital scalp). Knowing that hairs can move around the scalp and retain their pre-programmed preference of bald or not bald is the basis of hair transplant surgery.
Many men and women around the world have been able to hide their baldness by borrowing hair from the back of their head to fill in the gaps in the front. In addition, the combination of new medical therapies for hair loss along with surgery have meant that baldness can now be optional.