Here is Dr. John Cole (best in the business in my opinion) on BHT's in a discussion with Dr. Umar (also an experienced Doctor in BHT procedures).
Note: BHT's came into being because of extreme repair cases of men who didn't have enogh donor hair, but had already transplanted.
"Dr. Umar,
I’ve been involved in hair restoration surgery for over 15 years. Time has taught me one thing. Physicians have different opinions and different solutions.
Body hair in general does take on characteristics of the scalp. It typically will grow twice as long on the scalp as it did on the body. It’s growth rate increases when moved to the scalp.
Shock loss can occur from slits and it is has nothing to do with damage to the follicles. It is most likely a reaction to inflammation. It is more likely with dense packing than with lower densities.
The primary cause for poor growth with body hair is density. You should not be doing sessions exceeding 30 grafts per sq cm. This means 4000 to 6000 grafts in a session is the largest procedure you should be doing.
Extraction holes work wonderfully with body hair in FIT farming. They actually work better than slits, though slits work fine too. For that matter needle sites work well too. FIT farming not only re-populates the donor with hair (granted it is not the same quality as head hair), it also repopulates the area with melanin. Removal of head hair reduces the need for blood flow to the hair. This decrease in blood flow eliminates skin color. FIT farming adds hair so it also creates a requirement for blood flow to the hair and this too helps to create skin color.
Extraction sites appear larger than really are the when the graft is immediately removed. The extraction sites contract the first night and provide a very snug fit around fit farm hair. I do not see patients loose the fit farm hair at night when they sleep.
There is still quite a bit we need to learn about body hair transplanted to the scalp and to the donor area. I’m quite certain that ideas and techniques will change over time.
The primary problem with FUE, FIT, FUSE, etc., is that when you remove an intact follicular unit, you leave a gap. It is much better to put something in its place. In my experience FIT farmed donor areas look better than those that were not FIT farmed. Only God is perfect however. If I were looking for he Rolls Royce of procedures today, I would not look for a strip. I would look for a proven, successful means of individual follicular group removal. If you want to take it a step further, and you do not mind performing a similar procedure on your body hair, Fit Farming is good idea. Patients should be left to ponder their options and make their own decisions. Of course body hair is not nearly as good as scalp hair, but the supply of scalp hair is unfortunately quite limited. Therefore, we either have to look for ways to squeeze a little more scalp hair out of the donor area, or we have to use hair that is not as good quality wise (body hair).
I’ve been monitoring the rate of hair growth of body hair moved to the scalp and comparing it to the rate of growth on the body.
We know that the length increases to about twice its length original length when moved to scalp, if the hair grows. The questions proposed from this are whether the rate of growth increases or whether the duration of growth increases. I cannot yet comment about the latter, but our studies to date show that leg hair on the leg has a rate of growth of 0.3 mm per day, while leg hair on the scalp increases to 0.35mm per day. According to olsen, body and beard grow at 0.27 mm per day, while scalp hair grows at 0.37 to 0 .44 mm per day."