What is the donor area? Why does hair at the back of the head fall out less?

What is the donor area?

The word “donor” means “giver.” In a hair transplant, the donor area is the area from which we take the grafts (small pieces of tissue that contain a hair root together with the tissue around it). In most people, this is the back of the head along with the sides that run above and behind the ears.

This choice is based on a simple observation: as male pattern hair loss progresses, the hair at the front, in the mid-scalp and at the crown becomes sparse, while in most people the hair at the back and sides stays in place. Even in advanced hair loss, a horseshoe-shaped band of hair that runs around the back of the head from ear to ear is usually preserved.

A hair transplant moves the follicles (the roots that produce the hair) in this band to the thinning area, that is, to the recipient area. We describe the structure of the follicle in our article on the hair follicle.

Why is the hair at the back and sides more resistant?

In male pattern hair loss (androgenetic alopecia; hair loss linked to genetic predisposition and hormones), sensitive follicles shrink over time under the influence of a hormone called dihydrotestosterone (DHT), which is derived from testosterone, and produce finer and finer hairs. In most people, however, the follicles at the back and sides are less sensitive to this effect.

Part of this difference is linked to regional characteristics: follicles at the front and the crown usually have more hormone receptors (androgen receptors) and higher activity of the enzyme that converts testosterone into DHT (5-alpha reductase). Which follicles will be sensitive, however, is largely determined by your genes.

Donor dominance

The observation that makes hair transplantation possible is this: follicles taken from the back and sides usually keep their lower sensitivity to hair loss even after they are moved to a thinning area. In other words, this resistance depends more on the follicle itself than on where it is transplanted. This is called donor dominance (the characteristics of the area the follicle came from remain dominant). First described in the late 1950s, this principle is still the foundation of hair transplantation today.

This principle also has a practical consequence: a follicle taken from a part of the scalp that is sensitive to hair loss is expected to carry this sensitivity to its new place as well. That is why we make a point of taking grafts from the part that is expected to be least affected by hair loss.

What does donor dominance not mean?

Donor dominance describes a tendency; it does not mean that transplanted hair will never fall out. Possible reasons for transplanted hair falling out or thinning include:

• Transplanted follicles also continue the normal growth cycle and shed a hair from time to time. In the weeks after the transplant, some of the transplanted hair or the hair around it may also fall out temporarily; this is called shock loss.
• With age, hair can become finer across the scalp; the donor area and the hair transplanted from it can be affected by this as well.
• In some people, thinning does not follow a particular pattern and spreads across the whole scalp, including the back and sides. Because the donor area may also thin over time, a hair transplant is usually not recommended in this case.
• Donor dominance only describes resistance to the effect of hormones. Conditions linked to the immune system or to inflammation, such as patchy hair loss (alopecia areata) or scarring scalp conditions, can also affect the donor area and transplanted hair. If you suspect a condition like this, see a dermatologist for a diagnosis.

We also look at how transplanted hair behaves in the long term in our article on whether a hair transplant is permanent.

Where does the safe donor area begin and end?

Not every part of the donor area is equally resistant. The safe donor area is the part where the hair is expected to be least affected by hair loss in the long term; it usually covers the middle of the back of the head and the sides above the ears. The boundaries of this area do not follow the same line in everyone.

The main factors that determine the boundaries are:

• The course of your hair loss: The further your hair loss has progressed and the faster it is progressing, the narrower the safe area may be.
• Your age: At a young age, it is harder to predict how far hair loss will progress, so we draw the boundaries more cautiously.
• Your family history: Advanced hair loss in your family may be a sign that your band of hair could also narrow over time.
• Thinning in the donor area: If there are noticeably thinner hairs in this area too, the safe area may be narrower.

In female pattern hair loss, thinning often becomes noticeable in the mid-scalp and at the crown; the back of the head is usually less affected. In some women, however, the thinning also affects the donor area; in this case, a transplant is often not a suitable option.

Why is donor capacity limited?

Donor capacity is the total number of grafts that can be taken over your lifetime without leaving the donor area noticeably thin. This number varies greatly from person to person and is limited for three main reasons:

• A follicle that is taken is not replaced. Under normal circumstances, no new follicles form in adult scalp skin; a hair transplant does not increase the number of follicles you have.
• The donor area is visible too. The more grafts are taken from an area, the less hair is left there; beyond a certain point, the area looks sparse. In FUE, where grafts are taken one by one, a small, dot-like scar also remains at each point where a graft is taken; if too many grafts are taken, these scars may be easier to notice.
• Hair loss often progresses. A hair transplant does not stop the loss of your own hair in areas that were not transplanted. If the whole donor area is used in the first procedure, there may be no options left should a new need arise later.

The quality of the grafts also matters: thick or wavy hair, or hair close to your skin color, can give a fuller look with the same number of grafts.

For a beard transplant or an eyebrow transplant, grafts are also usually taken from this area; in other words, these procedures share the same limited resource as a hair transplant. That is why we plan the number of grafts based not only on the area that is thinning today, but also on what your donor area can provide in the long term. We explain the details in our article on how many grafts are needed.

Can beard and body hair be a secondary source?

In some people whose scalp donor capacity is very limited, hairs taken from areas such as the beard or chest can be transplanted to the scalp as an additional source. This is called a body hair transplant. We do not perform body hair transplants; this section is for general information only.

These hairs differ from scalp hair in several ways and have some limitations:

• Their growth phases are shorter. The growth phase of scalp follicles can last for years; for hairs in areas such as the chest, it is much shorter. That is why these hairs do not grow as long as scalp hair.
• Their thickness, curl and color may be different. For example, beard hairs are usually thicker and coarser than scalp hair; this difference can stand out among the hair on your head.
• There are fewer hairs per graft. Single-hair units are more common in body hair; groups of several hairs, as found on the scalp, are less common.
• Their results are less predictable. There is limited information on how they behave in the long term where they are transplanted.
• They leave scars where they are taken from. In areas that may be exposed, such as the chest or the beard, these small, dot-like scars may be noticeable.

What do we not know yet?

• Where does the difference between areas come from? Differences in hormone receptors and enzyme activity explain part of the picture; why these differences arise, however, is not fully known.
• Whose donor area will thin in the future? Age, family history and examination findings give clues, but they do not allow a definite prediction.
• Can donor capacity be increased? Research on multiplying follicles in the laboratory is ongoing; however, it is still at the experimental stage and is not a treatment that can be offered today.

How do we look at your donor area during the examination?

We base the plan on the current condition of your donor area. Together, we look at:

• How many follicular units (natural hair groups) there are in a given area, and how many hairs a unit usually has
• The thickness and curl of the hairs, and whether there are signs of thinning in the donor area
• The pattern of your hair loss, and where the boundaries of the safe area lie in your case
• Whether there are scars from a previous hair transplant or from another cause
• Whether the cause of the hair loss is clear

Sometimes we postpone the transplant and recommend that the cause of the hair loss be clarified first; sometimes medical treatment may come first. Only your doctor can determine, after assessing you, whether medication is suitable for you. If there is not enough healthy hair in the donor area, we may not recommend a hair transplant.

We describe the options for preparing the donor area (shaven, partially shaven or unshaven) on the hair transplant methods page.

Whether you are suitable for a hair transplant is determined during the examination, and results vary from person to person.