Clinical Characteristics of Follicular Units in Hair Transplants

Follicular Unit Constant

One of the interesting aspects of hair transplants with follicular units is that nature was kind to space them at approximately one per mm2. This has been observed clinically using densitometry and stereomicroscopic dissection and histologically using transverse microscopic sections of the skin (this was first described by Headington in 1984). Not only does a follicular unit constant of 1 unit/mm2 make the math easy, but it makes accurately estimating the donor harvest possible, and gives a logical basis for planning the density and distribution of the grafts.

The constancy of follicular unit density has been studied, but inconsistent study designs prevent accurate conclusions. There is general agreement on the following:

1. Follicular unit density generally decreases as work moves laterally from the mid-occiput at the level of the occipital protuberance towards the temples.

2. Follicular unit density varies among races such that the darker skinned races tend to have the lowest follicular unit densities and light-skinned races the highest.

3. Within the same race and same location on the scalp, there is significant person-to-person variation in follicular unit density. Read more