The donor zone theory (from where follicular units that are not prone to androgenetic alopecia are taken) in hair transplantation was proposed by Dr. Norman Orentriech in 1952 after a hair transplantation that was considered, at the time, a success.
During this event, hair was taken from the occipital part of the scalp and was implanted into the area subject to alopecia.
Dr. Orentriech then hypothesized that the hair that was taken from the occipital area had characteristics independent of the recipient area.
This type of study was first published in 1959.
Why is donor zone dominance important?
The donor zone concept in hair transplantation demonstrates how follicular units that are taken from the zone considered “safe” can regenerate new hair once transplanted. Since the transplanted UFs produce healthy hair in areas where previous hair has fallen out, it was concluded that the genetics of hair extracted from the occipital area is dominant over the recipient area.
Donor zone and dht
DHT (dihydrotestosterone) is a hormone that for some people binds with hair cell receptors and causes various forms of hair loss (miniaturization) in a progressive manner over time. Hair follicles in the donor zone however are considered resistant to the action of this hormone (as we mentioned at the beginning of the article). Therefore, the follicles of the donor area will continue to regrow regardless of the area where they are grafted.
The theory of donor area dominance therefore explains thatthere are hairs that are not sensitive to DHT that will continue to grow even in areas where androgenetic alopecia due to this hormone occurs.
Medicine and donor area, scholars’ objections.
There have been several diatribes between scholars and the donor zone theory. Dr. Norwood, the person in charge of the Hamilton/Norwood classification was the first physician to raise concerns towards this type of theory since he has always argued that a hair taken from one area slightly changes its characteristics once it is grafted into another (in a nutshell, it tries to resemble the hair born in that area).
Dr. Norwood observed that a smooth hair grafted into a glabrous area where there was initially curly hair became curly over time.
Dr. Orentriech’s theory, on the other hand, stated the opposite, i.e., that a harvested hair should retain exactly the native characteristics.
Another study of 2005 demonstrated the inaccuracy of Dr. Orentriech’s theory as hair was taken from the occipital area, grafted into a leg and it was observed that the hair started to grow more slowly (thus in agreement with the native regrowth times of leg hair).
Based on these results, we can say that the recipient area also has a very important impact on hair characteristics.
Is the donor-zone theory in hair transplantation valid?
Regardless of these studies we can say that the donor zone theory works in part since hair follicles maintain their characteristics of insensitivity to DHT but acquire some characteristics of the zone where they are grafted. Therefore, the theory can be considered partially valid.