The following chart shows the Norwood Classification system of hair loss, which gives general guidelines for the number of follicular unit grafts needed in the first hair transplant procedure.

Norwood hair Loss diagram
Norwood Hair Loss Diagram

Number of Hair Grafts in FIRST Hair Transplant Session*

Norwood Class Follicular Unit Grafts With Crown**
IIa 800-1400 -
III 1000-1600 -
III Vertex 1200-1600 1600-2200
IIIa 1400-1800 -
IV 1600-2200 2200-2600
IVa 1800-2400 -
V 2000-2500 2500-2800
Va 2200-2800 -
VI 2400-3000 2800-3400
VII 2500-3200 3000-3600
* The first session is usually designed as a stand-alone procedure. A second session would be considered for additional density, or if your hair loss progresses. Hair graft numbers in the upper part of the range are considered when the donor supply is adequate. For very large sessions, it is preferable to cut the existing hair in the transplanted area (if there is any) very short.

** Crown (or partial crown) coverage should be a goal in the first follicular hair transplant procedure only if the patient has an above-average donor supply and if limited hair loss is anticipated. If crown restoration is attempted prematurely, the person’s future options will be more limited and the chances for a cosmetically balanced hair transplant may be reduced.

There are a number of important goals that should be accomplished in the first hair transplant session. These include:

  • Creating, or reinforcing, the frontal hairline in order to establish a permanent frame to ones face.
  • Providing coverage to the thinning, or bald, areas of the scalp with the hair transplant extending at least to the vertex transition point.
  • Adding sufficient density in the first hair transplant session so that the results will look natural and that this procedure will “stand on its own.”

In the first hair transplant session, the entire area of the scalp that requires coverage should be transplanted, so that the surgical hair restoration may be completed as quickly as possible. One should not perform the hair restoration in sections or in arbitrarily small follicular hair transplant sessions. Additional sessions may be desired in the future, to add more fullness or to account for future hair loss, but everything that can reasonably be accomplished in one hair transplant session should not be spread over several procedures.

Second Hair Transplant Session

It generally takes from 10 to 12 months to see the full results of a follicular unit hair transplantation procedure. If a second hair transplant session is desired, it should be considered only after the hair from the first session has grown in. Over the course of the first year, the progressive increase in the hair’s diameter, texture and length can markedly change the look of the hair restoration and may influence the way the patient wants to groom his/her hair. Only after the hair has reached styling length can the patient and physician make the best aesthetic judgments regarding the placement of additional hair grafts.

Another reason to delay a second hair transplant session is that scalp laxity will continue to improve after the hair restoration for a period of up to 6-12 months making the donor hair easier to harvest.

Goals for the second hair transplant include:

  • Increase density in the previously transplanted areas
  • Further refine the hairline
  • Account for additional hair loss
  • Crown coverage when appropriate (see Follicular Unit Hair Transplantation)

Subsequent Follicular Hair Transplant Sessions

The total number of grafts needed for a complete surgical hair restoration can vary widely because of great variability between patients with respect to their hair characteristics, density, scalp laxity, head size and shape, facial characteristics and general aesthetic needs. The following table, therefore, serves only as a general guideline for the total number of hair grafts needed for each Norwood class.

TOTAL Number of Grafts for the Hair Restoration*

Norwood Class Follicular Unit Grafts With Crown*
IIa 1400-2200 -
III 1600-2400 -
III Vertex 1800-2600 2600-3200
IIIa 2000-3000 -
IV 2200-3400 3400-3800
IVa 2400-3600 -
V 2600-3800 3800-4500
Va 2800-4200 -
VI 3000-4600 4600-5600
VII 3200-5000 5000-6400
* The total number of follicular unit hair grafts, transplanted over one or more sessions, that is generally needed to accomplish a complete restoration.

Advantages of Large Hair Transplant Sessions

There are a number of surgical advantages in performing a large, first hair transplant procedure. In a virgin scalp (one that has not been transplanted before) the elasticity of the skin is intact, so that grafts can be placed more easily and will stay more securely in place. Another characteristic of a virgin scalp is an intact blood supply. This allows hair grafts to be placed close together without compromising their survival after the surgical hair restoration procedure.

In the donor area of a virgin scalp, both the density and scalp laxity are at a maximum, so that a relatively large amount of hair can be harvested and allow the incision to heal with the finest possible scar. In a virgin scalp, there is no distortion of follicular units, or altered hair direction from prior hair transplantation, so the follicular units are most easily extracted with their full complement of hair, providing maximum fullness to the hair transplant.

Each follicular hair transplant procedure causes some loss of potential donor hair due to destruction of hair adjacent to the wound edges, scarring in the donor area, distortion of the remaining hair follicles and a decrease in scalp laxity. Although these factors can be minimized in a well-planned hair restoration procedure that uses the most impeccable surgical techniques, they cannot be reduced to zero. Therefore, to maximize the total yield of hair, one should minimize the total number of hair transplant sessions.

Besides these technical issues, there are social reasons for performing the restoration quickly. Multiple, small hair transplant sessions, spread over an extended period, keeps the patient focused on the very problem he wanted to correct. The sooner the restoration is completed, the sooner the hair transplant patient can focus on other, more important aspects of his or her life. (see Follicular Transplantation)

Finally, in all hair transplant procedures there may be some associated shedding (telogen effluvium) in the recipient area. The hair that is at greatest risk of being shed is the hair that has started to miniaturize (a change in hair shaft diameter that can best be appreciated with a densitometer). Miniaturized hair is at the end of its life span, so when it is shed, it may not return. In areas where there is a high degree of miniaturization, the shedding may be cosmetically significant. Unless a substantial amount of hair is transplanted in these situations, there may be little benefit from hair restoration surgery.


Limits to Large Hair Transplant Sessions

Although the goal should be to accomplish the hair restoration as quickly as possible, there is a limit to the number of grafts that can be transplanted in one session. As the number of hair grafts placed per unit area (density) rises, so does the risk of vascular compromise (decreased blood flow to the area caused by injury to the scalp) and this may result in sub-optimal graft growth.

Other problems, such as graft elevation (popping), may cause the grafts to dry out and increase the risk of mechanical trauma during graft placing, become more likely as hair graft density is taken to extremes and these factors may also cause the sub-optimal growth of grafts.

The blood supply to the scalp is very rich and can generally support a large number of transplanted grafts in a single session. However, sun damage and smoking are some of the factors that can significantly compromise this blood flow and these risk factors must be identified in advance by the hair transplant surgeon.

Problems associated with decreased blood flow and popping are more closely related to the number of hair grafts placed in a specific area (density) rather than the absolute numbers of grafts placed. For this reason, the transplantation of a large number of follicular unit grafts over a large area does not create the same problems as creating very high densities in one specific area.

However, transplanting large number of grafts (in “mega-sessions”) poses its own challenges, such as increasing the time the grafts remain outside the body, requiring more surgical staff, contributing to patient and staff fatigue, and creating organizational issues. As with dense-packing, the use of very large hair transplant sessions should be reserved for only the most experienced surgical teams.

Another important factor affecting blood flow is the size of the hair grafts and, therefore, the size of the recipient sites. Larger recipient sites cause significantly more damage to the blood supply than smaller ones and will severely limit the number of grafts that can be placed at one time. Fortunately, a major benefit of hair transplantation performed exclusively with follicular units is that you can place the most hair in the smallest possible recipient sites. (see Logic of Follicular Unit Transplantation)

Very large follicular hair transplant sessions also require a large amount of donor tissue. Since one has 90 to 100 follicular units per square cm of donor tissue, in Follicular Unit Hair Transplant procedures, the hair restoration doctor should be able to obtain from 90 to 100 follicular grafts for every cm2 of tissue harvested. Therefore, a 2,400 graft procedure will require an incision that is 1cm wide and slightly more than 24 cm in length. A 4,000 hair graft session will require a 1.5 cm wide incision that is more than 27 cm in length. Although a 1 cm incision usually heals with a fine hairline scar, incisions of 1.5 cm or more significantly increase the risk of a widened scar. A wide donor scar can potentially be a cosmetic problem and can limit the amount of hair that can be obtained in future hair transplant sessions.

Proper patient selection and a surgical team highly skilled in hair restoration help avoid such problems, but the risks will increase if the number and density of grafts increase. Because these factors are inherent to all hair transplant procedures, it is important that the physician focus on maximizing graft growth, rather than simply seeking some arbitrarily high target number of grafts. What is ultimately critical for the patient is not how many grafts were transplanted, but how many actually grow. (see Follicular Unit Hair Transplantation).

Commentary: How large should hair transplant sessions be?

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Graft Numbers

In Follicular Unit Hair Transplantation, the goal should be to achieve the best possible cosmetic result in the context of the patient’s total donor reserves, rather than trying to place as many grafts as possible in one hair transplant session. Read more about Large Hair Transplant Sessions.

Splitting Up Follicular Units

As a word of caution, in Follicular Unit Hair Transplantation, stereo-microscopic dissection is used to dissect naturally occurring 1-4 hair follicular units from the donor area. If these units are kept intact in the dissection, growth will be maximized and a hair transplant patient will get the greatest possible fullness and density. However, if the microscopic dissection is poor and some of the hair in the follicle is destroyed, the results will be less than ideal.

If follicular units are divided up into smaller groups, or into individual hairs, the graft numbers will significantly increase (and so will the price of the hair restoration procedure, if the patient is charged by the graft) without any increase in fullness (and probably less fullness due to sub-optimal growth.)

For example, if a patient had a 2,000 graft hair transplant procedure where the 4-hair grafts were split up into 1- and 2-hair grafts, either through poor dissection or intentionally, the new procedure would now have 2,400 grafts with exactly the same number of hairs. However, now each graft would contain only 1.96 hairs rather than 2.35 hairs. In addition, 400 more sites would need to be unnecessarily placed into the patients scalp to accommodate these grafts. This, in turn, would cause the hair to be spread out over a larger area of the scalp, decreasing the potential density in the more important areas such as the front – and increasing the cost of the surgical hair restoration procedure.

Splitting Follicular Unit Hair Grafts

FU Graft Size Intact FU Grafts Split FU Grafts
1-hair 250 650
2-hair 1000 1200
3-hair 550 550
4-hair 200 0
Total Grafts 2000 2400
Total Hairs 4700 4700
Hair/FU Graft 2.35 1.96

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