Hair transplantation is based on an understanding of how hair follicles grow, why some follicles are more resistant to hair loss and how healthy follicles can be relocated to areas where hair has been lost. Rather than simply replacing missing hair, transplantation works with the biology of the individual follicle to create lasting growth.
Understanding the structure and behaviour of hair follicles can make the process easier to understand and help explain why donor selection, graft handling and placement are so important. This guide explores the trichology behind hair transplantation, from the hair growth cycle and follicle biology to harvesting, implantation and long term regrowth.
What is a hair follicle?
A hair follicle is a small structure within the skin responsible for producing a hair. Each follicle contains several components that work together to control hair growth, including the hair bulb, where new hair cells are produced, and the dermal papilla, which plays an important role in regulating follicle activity.
Hair follicles do not produce hair continuously at the same rate. Instead, they move through a repeating growth cycle. Understanding this cycle is fundamental to understanding both hair loss and hair transplantation.
The main stages are the anagen phase, when the follicle actively produces hair, the catagen phase, when growth slows and the follicle undergoes transition, and the telogen phase, when the follicle rests before the hair is shed and a new growth cycle begins.
The length and behaviour of these phases vary between individuals and can be affected by genetics, hormones, age, health and other factors.
Why do some hair follicles resist hair loss?
One of the most important principles behind hair transplantation is known as donor dominance. Hair follicles located towards the back and sides of the scalp are generally more resistant to the effects of dihydrotestosterone, commonly known as DHT, in people with androgenetic hair loss.
DHT can cause susceptible follicles to gradually become smaller. This process is known as follicular miniaturisation. Over time, affected follicles produce progressively finer and shorter hairs until visible density is significantly reduced.
Follicles in the donor region can retain their resistance to this process when transplanted to another area of the scalp. This is the biological principle that allows transplanted follicles to continue producing hair in areas affected by pattern hair loss.
However, not every person has the same donor characteristics. Assessing the density and health of the donor area is therefore an important part of determining whether transplantation is appropriate.
>What happens to hair follicles during a transplant?
A hair transplant involves carefully moving follicular units from a donor area to a recipient area affected by hair loss. A follicular unit may contain one, two, three or occasionally more individual hairs growing naturally together.
The objective is to preserve these natural groupings wherever possible. This allows transplanted hair to grow in a way that reflects the natural characteristics of the surrounding hair.
During the procedure, follicles are removed from the donor area using either Follicular Unit Extraction or Follicular Unit Transplantation. The selected technique affects how the follicles are harvested, but both approaches aim to preserve healthy grafts for placement in the recipient area.
The surgeon then creates recipient sites at carefully selected angles and positions. The follicles are placed into these sites so that the direction, angle and distribution of the new hair complement the existing growth pattern.
FUE and FUT: How are hair follicles harvested?
The two established approaches to follicle harvesting are Follicular Unit Extraction and Follicular Unit Transplantation.
With Follicular Unit Extraction, individual follicular units are removed directly from the donor area. This leaves small marks that generally become difficult to see as they heal.
With Follicular Unit Transplantation, a narrow section of skin containing follicular units is removed from the donor area. The follicles are then separated under magnification before being prepared for transplantation.
The choice between the techniques depends on factors including donor characteristics, the number of grafts required, hair style and individual circumstances. There is no single technique that is appropriate for everyone.
The International Trichology Society promotes greater understanding of hair and scalp biology, including the importance of considering individual follicle characteristics when assessing hair loss and restoration.
How many hair follicles are needed for a transplant?
The number of grafts required depends on the extent and pattern of hair loss, the size of the treatment area and the density available in the donor region.
A person with recession around the temples may require considerably fewer grafts than someone experiencing extensive thinning across the front and central scalp. Similarly, crown restoration requires careful consideration because the direction and natural pattern of growth can make density appear different from other areas.
| Area of hair loss | Typical graft range |
| Receding hairline and temples | 1,000 to 2,000 |
| Front and mid scalp | 2,000 to 3,500 |
| Crown | 1,500 to 3,000 |
| Extensive restoration | 3,500 to 6,000 or more |
These figures are illustrative rather than a standard prescription. Graft requirements should be determined following an assessment of the hair loss pattern, donor density and long term restoration goals.
What happens to transplanted hair follicles after surgery?
Understanding the hair growth cycle helps explain why transplanted hair does not immediately produce visible new growth.
Following transplantation, the visible hair attached to the follicle may shed during the first few weeks. This is commonly referred to as shock shedding and is a normal part of the process. The follicle itself remains within the scalp and can subsequently enter a new growth phase.
New growth generally begins to become visible after several months. Around three to four months, early growth may start to appear, while more noticeable density usually develops between six and nine months.
The final result can take 12 to 18 months as the transplanted follicles continue to produce and thicken new hair.
This gradual process reflects the natural behaviour of the hair follicle rather than an immediate cosmetic change.
Why does hair transplant placement need to be precise?
Hair follicles do not grow vertically from the scalp. Their direction and angle vary according to their location and surrounding hair.
A natural hairline, for example, usually contains finer hairs and follows a carefully changing direction. Hair towards the centre and crown follows different patterns.
For this reason, successful transplantation involves more than simply placing grafts into areas where hair is missing. The position, angle, direction and distribution of each graft can influence how natural the final result appears.
Understanding follicular anatomy and natural hair growth patterns is therefore an important part of hair restoration planning.
Is transplanted hair permanent?
Hair transplantation can provide long term growth because the follicles selected from a suitable donor area generally retain their resistance to the processes responsible for pattern hair loss.
However, transplantation does not stop the underlying tendency to lose susceptible hair. Existing follicles that were not transplanted may continue to become thinner over time.
This is why a long term approach to hair loss is important. Depending on the diagnosis, medical treatment or other approaches may be considered to help maintain existing hair alongside transplantation.
The aim should be to manage the hair and scalp as a whole rather than focusing only on the area receiving transplanted follicles.
What can affect hair follicle health?
Hair follicle behaviour can be influenced by genetics, hormones, ageing, nutrition, illness, medication and scalp health. Different forms of hair loss can affect follicles in different ways, which is why identifying the cause is an important part of any hair restoration assessment.
For example, androgenetic alopecia involves progressive miniaturisation of susceptible follicles, while telogen effluvium is associated with an increased number of follicles entering the resting phase. Other conditions can cause inflammation or permanent damage to follicles.
A trichological assessment can help establish the likely cause and pattern of hair loss before transplantation is considered.
Frequently Asked Questions
Here are some commonly asked questions about hair follicles and hair transplantation:
What is a hair follicle and why is it important for hair transplantation?
A hair follicle is the structure within the skin that produces a hair. Its health, size and growth behaviour determine the quality and longevity of the hair it produces. Hair transplantation relies on moving healthy follicles from a suitable donor area to areas affected by hair loss.
Why are donor hair follicles important in a hair transplant?
Donor follicles are important because they provide the hair that will be relocated during transplantation. Follicles from the back and sides of the scalp can be more resistant to the effects of DHT in people with pattern hair loss. Assessing donor density and follicle health is therefore essential when planning a transplant.
What happens to hair follicles after a hair transplant?
After transplantation, the visible hair may shed during the early weeks while the follicle remains within the scalp. The follicle can then enter a new growth phase, with new hair typically becoming visible after several months. The final result develops gradually as the transplanted follicles mature.
Can transplanted hair follicles fall out again?
Transplanted follicles from a suitable donor area are generally selected because of their resistance to the processes responsible for pattern hair loss. However, existing non transplanted follicles can continue to thin over time. Long term management may therefore be important even after transplantation.
How does trichology help with hair transplantation?
Trichology focuses on the science of hair and scalp health. A trichological assessment can help identify the cause and pattern of hair loss, examine the condition of the scalp and donor area, and determine whether transplantation may be appropriate.
Understanding how hair follicles function provides a clearer picture of why hair transplantation can work and why careful assessment is so important. If you want to understand your hair loss, follicle health and potential treatment options in greater depth, explore the educational resources provided by the International Trichology Society or seek guidance from a qualified trichology professional. An informed assessment can help you understand the condition of your hair and scalp before deciding whether hair transplantation is appropriate for you.
