When hairs are transplanted they typically undergo a traumatic experience that causes them to typically fall out briefly. The cells that make the hair are not lost, but the transplanted hair shaft is usually shed for a period of time. This shedding of hair is called effluvium. When hairs undergo effluvium, the living cells of the dermal sheath will move toward the surface of the skin like an accordion compressing. These cells will usually remain dormant for a number of months before they begin to produce hair again. This entire process is called anagen effluvium. The duration of anagen effluvium will last between 3 and 18 months. No one knows why it is so short for some hairs and so long for others. Most of the hair, however will resume growth by the 8th month. A good general rule of thumb is that about 30% will resume growth some time during the 3rd month and then about 10% more will follow during each successive month. You may find that at 3 months there is no growth, but then 2 weeks later you might see 30%. Hairs are strange structures and they are poorly understood. They are the only structure on the human body that grows, rests, falls out, and then begins a new anagen cycle after a period of rest.
Some times you will find a few hairs that do not fall out. They just keep on growing. Those hairs that do not fall out will sometimes show signs of the trauma they recently experienced. There are anatomical changes in these hairs that reveal a time line so that you can identified when the trauma occurred. This is similar to the changes in the earths' surface when major events occurred such as the large meteor that supposedly is responsible for the extinction of the dinosaur. This does not happen to all the hairs that continue to grow. When it does occur, you can clearly identify the hair as a transplanted hair and you can identify when the trauma occurred.
The enclosed photograph shows one of these hairs. You can see the distal end of the hair is thicker and has more pigmentation. Suddenly, the hair changes from a dark, coarser hair to a finer hair. You can see this line of demarcation. This sudden reduction in diameter identifies the traumatic event the hair experienced during hair transplantation. Thes hairs will often remain fine for many subsequent months and only gradually does the pigmentation and diameter return to normal.
It is also worth noting that one reason that it can take so long for body hair to produce a cosmetically significant illusion of coverage is because body hairs are even more prone to begin as finer hair structures that take several months to gain cosmetically significant diameter.
All hairs on the scalp have a specific number of cycles (anagen, telogen, effluvium, resumption of anagen). You can think of it as the number of lives a cat has. Once a hair reaches the critical number of cycles, it is thought to abruptly transform form a coarse thick terminal hair to a finer, slower growing, less pigmented hair that will have a shorter anagen duration or a shorter growing phase. Treatments aimed at hair loss include medications such as Propecia or finasteride. Propecia is known to competitively inhibit 5 alpha reductase type 2. this results in a decrease in Dihydrotestosterone (DHT). How does DHT reduction promote hair growth? No one knows for sure, but it probably has something to do with stimulation and prolongation of anagen. It is not uncommon for individuals on Propecia to experience a shedding of hair 3 to 6 months after beginning the product. Many individuals are understandably frightened out of their minds over this. It probably is a good sign, however. It probably indicates that the propecia has stimulated a new anagen cycle. When a new anagen cycle is stimulated, the resting hair in telogen phase is pushed out much like a baby tooth is pushed out of the way by an adult tooth. Thus, 8 to 12 months after this shedding, you should see a thicker shock of hair.
Many individuals do not want to take pharmaceuticals. Therefore, they should focus on products that will promote or prolong anagen. These include other pharmaceuticals such as Avodart (dutasteride), Rogaine (minoxidil), and Nizoral shampoo. Natural products that prolong anagen include Hair Cycle shampoo and conditioner, as well as, saw palmetto.
How can increasing the duration of anagen prolong the life of your hair? Suppose that every hair has 10 cycles or lives and products such as Hair Cycle shampoo increase the duration of each cycle by 2 years. A single hair might now have an extended life span of 20 years.