Follicular Units

The underlying dictum of follicular unit transplantation is that intact, individual follicular units are sacred. They should neither be broken up into smaller units, nor combined into larger ones. This simple idea was first introduced in the 1995 landmark article “Follicular Transplantation” by our group. This may not seem like a radical approach to hair transplantation as we are now well into the early 21st centruy, but when viewed in the context of how the surgery has been performed over the past fifty years (when the very existence of the follicular unit went generally unrecognized), and how it has transformed the field in the past four years, it is radical indeed.

Even now, when follicular units are at the focal point most hair transplant meetings, there is a disturbing trend to not only ignore the importance of the follicular unit, but to ignore the integrity of the follicle itself in order to save time and expense in performing the transplant. The new FUE surgeons are talking about breaking up the follicular unit when doing the surgery. This makes no sense to me. They claim it is a small price to pay for FUE efficiency. That, again, makes no sense to me. That is why it is so important for you, the patient, to be an “educated consumer.”

The follicular unit was first defined by Headington in his 1984 paper “Transverse Microscopic Anatomy of the Human Scalp”. The follicular unit includes:

  • 1 to 4 terminal follicles – thick hair unaffected by male hormones vestigial
  • 2 vellus follicles – very fine hair that has little cosmetic significance
  • sebaceous (oil) glands
  • a tiny vestigal muscle
  • small blood vessels
  • fine nerves
  • perifolliculum – collagen that surrounds the follicular unit

The above photo-micrograft was taken at the level mid-dermis in the skin. Note the discrete 1-, 2-, 3-, and 4- haired follicular units as they lie naturally in the skin.

This photo shows perfectly dissected 1, 2, 3, and 4-hair individual follicular units using a stereo-microscope.


Because of the complex interaction of all of the various parts of the follicular unit, it is important to keep it intact during the transplant. Although the most obvious reason to keep the follicular unit whole is an economy of size, i.e. it is a way to get the most hair into the smallest possible site, and create the smallest wound with the least damage to the graft. It is also important to maximize growth and intact follicular unit, when properly handled, get maximum growth. It has been shown that when single-hair micrografts are generated from breaking up larger follicular units, their growth is less than when the follicular units are kept intact.

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The Reason for Using Only Individual Follicular Units

Scalp hair grows in follicular units, rather than individually. This is most easily observed by densitometry, a simple technique whereby scalp hair is clipped short in a very small area and then observed via magnification in a 10mm field (please see Art and Science of Minigrafting for more information). What is very obvious when one examines the scalp by this method, is that follicular units are relatively compact, but are surrounded by substantial amounts of non-hair bearing skin. The actual proportion of non-hair bearing skin is probably on the order of 50%, so that its inclusion in the dissection, (or its removal) will have a substantial effect upon the outcome of the surgery. When multiple follicular units are used, the additional skin that is included will adversely affect the outcome of the surgery, by necessitating larger wounds, making the healing slower and often causing irregularities of the skin surface.

The transplantation of multiple follicular units, often requires recipient skin to be removed (via punch or laser) to allow this new volume of tissue to fit into the recipient site and/or to avoid unsightly compression of the newly transplanted grafts. In effect, the richly vascular thick donor scalp, is transplanted into a thinner recipient area, in which tissue is further removed to allow the graft to fit. Not surprisingly, the results of this technique will often look unnatural!

A great advantage of using individual follicular units is that the wound size can be kept to a minimum, minimizing any impact on the vascular network that is present while at the same time maximizing the amount of hair that can be placed into it. Having the flexibility to place up to 4 hairs in a tiny recipient site has important implications for the design and overall cosmetic impact of the surgery. It is a major advantage that follicular unit transplantation has over extensive micrografting in minimizing or eliminating the “see through” look that is so characteristic of the latter procedure.

Of course the main reason for transplanting only individual follicular units is that is the way hair grows. By following the way hair grows in nature the doctor can insure that the transplant will look totally natural. There is really no other way. Any grouping larger than the naturally occurring follicular unit will run the risk of a pluggy, tufted look. A problem that is a disaster for the patient and so easily prevented using only individual Follicular Units.

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The Importance of Keeping Recipient Sites Small

Using only follicular units enables the recipient sites to be kept very small. In fact, in Follicular Unit Transplantation the sites are so small that they are made with a specialized 18-gauge needle that is about the size that is used in a routine blood test.

The importance of minimizing the wound size in any surgical procedure can not be over emphasized and hair transplantation is no exception. The effects of recipient wounding are felt at many levels. Larger wounds tend to injure larger blood vessels and although the blood supply of the scalp is extensive, the damage to these vessels can have a deleterious impact on blood flow to the tissues.

Especially when transplanting large numbers of grafts per session, it is important to keep the recipient wounds as small as possible so that growth will be maximized. The compact follicular unit is, of course, the ideal way to permit the use of the smallest possible recipient site, and has made the transplantation of large numbers of grafts technically feasible (please see Follicular Transplantation for original article.)

Excision, which includes removing tissue via a punch or laser (please see Laser Hair Transplantation) causes more damage to tissue then an incision (slit). But since there are no absolute guidelines as to the ideal number, or densities of grafts, that can be used and still ensure maximum growth, the practitioner must rely on his clinical judgement in this regard. It is recommended that one be conservative until one has significant clinical experience using large numbers of grafts. In addition, there are a host of systemic and local factors that should be taken into account when planning the number and spacing of the recipient sites, regardless of their size (please see Aesthetics of Follicular Transplantation).

Another important advantage of the small wound is a factor that can be referred to as the “snug fit.” Unlike the punch, which destroys recipient collagen and elastic tissue, a small incision, made with a needle, retains the basic elasticity of the recipient site. When a properly fitted graft is inserted, the recipient site will then hold it snugly in place. This “snug fit” has several advantages. During surgery, it minimizes popping and the need for the sometimes traumatic re-insertion of grafts. After the procedure, it ensures maximum contact of the implant with the surrounding tissue, so that oxygenation can be quickly re-established. In addition, by eliminating empty space around the graft, there is less clot formed, and wound healing is facilitated.

Since oxygen reaches the follicle by simple diffusion, its ability to do so is a function of tissue mass. Unlike larger grafts whose centers can become hypoxic (in a state of oxygen deprivation), the slender follicular unit presents little barrier to this diffusion, thus ensuring uniform oxygenation.

It is important to note that when trying to place larger grafts (either round or linear), into a small site (kept small to minimize tissue injury) compression of the grafts is an undesirable consequence, and may result in a tufted appearance. In contrast, when transplanting follicular units, there are no adverse cosmetic effects of compression, since follicular units are already tightly compacted structures.

Large wounds cause a host of other cosmetic problems including dimpling, changes in skin pigment at the border of the graft, depression or elevation of the grafts, or a thinned, atrophic (scrawny) look. The key to a natural appearing hair transplant is to have the hair emerge from perfectly normal skin just like it would from its original pore. The only way to ensure this is to keep the recipient wounds small.