In eyebrow transplant procedures, hair follicles from the back of the head are used as the donor site. The main reason for this is the high resistance of the hair follicles in the back of the head to hair loss. However, transplanting these grafts—which are biologically hair follicles—into the eyebrow area triggers an interesting physiological process.

Hair strands and eyebrow hairs have different characteristics in terms of growth rate, thickness, and growth cycle duration. For this reason, one of the processes patients are most curious about and experience after surgery is Growth of Transplanted Eyebrows and then comes the adaptation of these hair follicles to their new locations.

In the Long FUE eyebrow transplant procedures performed at our clinic under the leadership of Dr. Handan Yavuz, the adaptation process of the hair follicles is closely monitored in light of scientific data. After the hair follicles are transplanted into the eyebrow area, they gradually begin to adopt the microenvironmental characteristics of their new location. In this article, we will discuss in detail the behavior of hair follicles in the eyebrow area, their growth rates, the changes in their characteristics over time, and the biological mechanisms underlying this process. This will help you better understand how long-term aesthetic results following eyebrow transplantation are optimized.

Differences in the Biological Cycles of Hair and Eyebrow Hairs

To understand the growth patterns of hair follicles, we must first examine the life cycle of the hair follicles in our bodies. Each hair follicle goes through three basic stages:

• Anagen Phase (Growth Phase): This is the period during which hair actively grows. While this phase lasts between 2 and 7 years for scalp hair, it lasts only about 2 to 4 months for eyebrow hair. The reason scalp hair grows so much is that the anagen phase is long. The short growth phase in the eyebrow area ensures that the hairs there remain at a certain length.
• Catagen Phase (Transition Phase): This is a temporary phase lasting several weeks during which hair growth stops and the follicle shrinks. During this phase, the follicle prepares for the resting phase, and the hair shaft begins to detach from the root.
• Telogen Phase (Resting Phase): Kılın döküldüğü ve kökün yeni bir kıl üretmek için dinlendiği evredir. Kaşlarda kıl köklerinin büyük bir kısmı bu evrede bekler, bu yüzden kaşlarımız saçlarımız gibi sürekli ve kontrolsüzce boy atmaz. Kaş kıllarının yaklaşık %90’a yakını telojen fazda bekleyerek dökülmeyen stabil yapıyı korur.

Follicles harvested from the nape of the neck are transplanted to the eyebrow area along with their anagen phase memory (potential for 2–7 years of growth). For this reason, in the first few months following the transplant, the hairs growing from the transplanted follicles tend to grow as quickly as scalp hair. This is a completely normal and expected occurrence. Over time, however, this rapid growth is regulated by the body’s natural adaptation process.

What Is Recipient Co-Dominance?

So, do the transplanted hair follicles continue to grow as quickly as natural hair for the rest of one’s life? The medical community’s answer to this question is “partially no.” This is where “Recipient Co-Dominance” or the theory of tissue adaptation comes into play.

The hair follicle begins to adapt to the blood circulation, hormonal stimuli, and local growth factors in its new location. The subcutaneous tissue in the eyebrow area is thinner than that of the scalp, and the blood flow rate there does not nourish the hair follicle as intensely as it does on the scalp. Over time, under the influence of these local factors, the biological cycle of the transplanted hair follicle undergoes a change. The follicle’s anagen (growth) phase shortens, while the telogen (resting) phase lengthens.

The fact that the level of oxygenation in the subcutaneous tissue is lower than that in the scalp, in the hair follicle keratin slows down the synthesis. As a result, the hair follicle begins to grow more slowly over time, while the diameter of the hair shaft thins, gradually taking on the form of a natural eyebrow hair. This adaptation, also known as the “eyebrowization” process of hair follicles, continues for 2 years following the procedure.

These microenvironmental changes occur at the level of gene expression. Hair follicle cells slow down their own genetic growth rate in response to chemical signals from the neural and vascular networks in the eyebrow region where they have newly settled. This slowing down is the most fundamental biological evidence that hair-like roots gradually take on the characteristics of eyebrow hair over time.

Changes in Thickness of Transplanted Eyebrows and Trichological Analysis

According to our clinical observations and trichological (the study of hair) measurements, the diameters of hair strands taken from the donor area range on average from 70 to 90 microns (µm). The thickness of the original eyebrow hairs varies from person to person but is generally between 40 and 55 microns. When hair follicles are first transplanted into the eyebrow area, they continue to grow at their original thickness (70–90 microns). This causes the eyebrows to appear slightly stiffer and thicker than normal during the first few months.

Ancak 12. aydan itibaren başlayan yerel doku adaptasyonu sayesinde, kıl foliküllerinin çaplarında küçülme (minyatürizasyon) gözlemlenir. 24. ayın sonunda yapılan trikolojik ölçümlerde, ekilen kılların kalınlığının ortalama 55-65 mikron seviyesine kadar gerilediği tespit edilmiştir. Kıl şaftındaki bu %20 ila %30 oranındaki incelme, ekilen kaşların doğal kaş kıllarıyla mükemmel bir şekilde harmanlanmasını sağlar. Kıllar sert yapısını kaybederek daha yumuşak ve kavis alabilir bir forma bürünür.