Since its ﬁrst introduction in 2002, follicular unit ex-
traction (FUE) has become an increasingly more popular
method of obtaining donor hair.1
Despite the various advantages and disadvantages of FUE,
it is likely that more patients choose to undergo hair trans-
plantation by FUE than follicular unit strip surgery (FUSS)
because less pain and scarring is associated with FUE. Never-
theless, the efﬁcacy of FUE has been questioned with respect
to whether its outcomes are equivalent to those of FUSS, the
most commonly employed procedure by many hair surgeons.
Some expert hair surgeons have simultaneously per-
formed FUSS and FUE in the same patient. Long-term
comparisons of the 2 methods have revealed much lower
follicle survival rates in FUE than FUSS (53.9% versus
85.2%, respectively).2 FUE-harvested grafts contain less
perifollicular tissue than do FUSS-harvested grafts, and
many physicians evidently believe this to be the main
cause of the lower survival rate of harvested follicles in
FUE than FUSS. Nonetheless, the same expert surgeons
have found that there is a tendency toward a larger de-
viation of surgical outcomes of FUE than FUSS. In cases
in which the same surgeon consistently harvested the fol-
licles by the same method, both excellent and poor results
were observed. This raises 2 important clinical questions:
What characteristics of FUE-obtained grafts, other than
the smaller amount of perifollicular tissue compared
with FUSS-obtained grafts, contribute to this variation in
outcomes? How does the appearance of FUE- and FUSS-
obtained grafts differ under a microscopic and high-mag-
Microscopic dissection is generally chosen for FUSS.
However, although an approximately ×5 magnifying loupe
Copyright © 2017 The Authors. Published by Wolters Kluwer Health,
Inc. on behalf of The American Society of Plastic Surgeons. This is
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(CCBY-NC-ND), where it is permissible to download and share the
work provided it is properly cited. The work cannot be changed in
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From the Dana Plastic Surgery Clinic, Gangnam-gu, Seoul, Korea.
Received for publication October 14, 2016; accepted January 20,
Background: When performing follicular unit extraction (FUE), various types of
minor hair follicle trauma unapparent during follicular unit strip surgery are likely
to occur. However, no studies have examined such damage.
Methods: In total, 100 grafts were randomly selected from each of 42 patients who
underwent FUE with a 1-mm-diameter sharp punch. A ×5.5 magnifying loupe and
a ×60 magnifying binocular microscope were used. The transection rate (TR), par-
ing, fractures of and damage to the dermal papilla (DP) areas, and hair bulb par-
tial injury were assessed.
Results: Observation with the magnifying loupe revealed an average TR of 7.40%,
and 4.31, 1.90, 1.52, and 0.43 hair follicles per 100 grafts exhibited paring, fracture,
DP partial injury, and hair bulb partial injury, respectively. An average of 9.21 telo-
gen hairs were observed. Microscopic examination revealed a TR of 6.34%, and
9.07, 1.95, 0.79, and 1.24 hair follicles per 100 grafts exhibited paring, fracture, DP
injury, and hair bulb partial injury, respectively. An average of 16.62 telogen hairs
Conclusions: Various types of minor hair follicle damage occur during FUE as
shown by loupe and microscopic examination of the grafts. Especially paring and
hair bulb injury were more apparent under microscopic examination. These mi-
nor hair follicle injuries should be considered when choosing operative method
or surgical techniques. (Plast Reconstr Surg Glob Open 2017;5:e1260; doi: 10.1097/
GOX.0000000000001260; Published online 16 March 2017.)
Jae Hyun Park, MD, PhD
Seung Hyun You, MD
Various Types of Minor Trauma to Hair Follicles
During Follicular Unit Extraction for Hair
Disclosure: The authors have no ﬁnancial interest to
declare in relation to the content of this article. The Article
Processing Charge was paid for by the authors.
PRS Global Open • 2017
is recommended for FUE, some surgeons perform this
procedure with the naked eye or by wearing a simple ×1.5
or ×2.0 magnifying glass. The grafts harvested in this way
might then be inspected by the naked eye, a ×1.5 to ×2.0
magnifying glass, and a ×5 magnifying loupe to conﬁrm
whether they are intact or properly transected.
Until now, we have only considered either the occur-
rence of transection or the presence of intact grafts to
assess the quality of follicles harvested by either FUE or
FUSS. We believe that the transection rate (TR) provides
valuable information about the quality of FUE surgery.
However, in addition to simple transection, the occur-
rence of other types of minor trauma to the follicles har-
vested by FUE is probable, and these types of trauma are
rarely seen in FUSS.
FUSS lacks various potentially traumatic processes
such as dissection using a rotating or oscillating punch
and extraction using aid-to-extraction forceps or jeweler’s
forceps. Hence, in the present study, we aimed to identify
other types of hair follicle injuries that can occur in addi-
tion to transection.
To the best of our knowledge, no reports have ad-
dressed the nature and extent of these types of minor
hair follicle trauma. Therefore, we conducted the present
study to determine the frequency and nature of minor
trauma that occurs during FUE surgery.
MATERIALS AND METHODS
This study included 42 patients (38 males and 4 fe-
males) at the authors’ clinic. Using a 1-mm-diameter
sharp punch, 100 follicles were randomly selected from
each patient. In total, 4200 grafts were analyzed.
Patients with a history of hair transplant surgery, infec-
tious disease, or trauma in the donor area were excluded
from the study. The patients’ age distribution ranged from
28 to 52 years, and the mean age was 32.6 years. All male pa-
tients exhibited Norwood stage 3 to 5 male pattern baldness.
All female patients were undergoing female hairline correc-
tion without female pattern hair loss. The donor area of all
patients was shaved in the form of a total or partial patch for
FUE. This study was approved by the internal institutional re-
view board of the Korea National Institute of Bioethics Policy.
All punching was performed by 1 expert hair surgeon
(Dr. Park). A 1-mm sharp punch of the Folligraft system
(LeadM Corp., Seoul, Korea) was used. The surgical pro-
cedure was implemented in the same manner as routinely
performed during a normal FUE operation. A FOX test was
conducted at the beginning and in the middle of the sur-
gery, while the punching depth was modiﬁed. The punching
depth achieved was within 2.5 to 3.5 mm (mean, 2.9 mm).
All injuries were divided into 5 types: transection, par-
ing, fracture, dermal papilla (DP) injury, and hair bulb
partial injury. The presence or absence of such injuries
was conﬁrmed in all patients. A ×5.5 magnifying loupe and
×60 magnifying binocular microscope were employed for
analysis. If none of the above-described 5 types of injury
was present, the hair follicle was considered intact.
An independent-samples t test was conducted to deter-
mine the differences in the types of partial injuries in all
The TR was 7.40% based on microscopic observation
and 6.34% based on loupe observation. The difference
in these rates was not signiﬁcantly different (P > 0.05).
However, the 2 observation methods showed signiﬁcantly
different numbers of telogen hairs: an average of 9.21 fol-
licles based on loupe observation and an average of 16.62
follicles based on microscopic observation (P < 0.001;
Paring was present in approximately 4.31 follicles
based on loupe observation and 9.07 follicles based on mi-
croscopic observation; microscopic observation showed a
2-fold higher number of affected follicles, and the differ-
ence was statistically signiﬁcant (P < 0.000).
DP partial injury affected an average of 0.52 follicles based
on loupe observation and 0.79 follicles based on microscopic
observation with no signiﬁcant difference (P > 0.243).
Bulb injury affected an average of 0.43 and 1.24 fol-
licles based on loupe and microscopic observation, respec-
tively, with a signiﬁcant difference (P < 0.003).
Finally, an average of 1.90 follicles were fractured based
on loupe observation and an average of 1.95 follicles were
fractured based on microscopic observation, with no sig-
niﬁcant difference between the 2 methods (P > 0.858).
Trauma was more frequently found in association with
all types of damage under microscopic examination. How-
ever, a statistically signiﬁcant difference appeared only for
paring and bulb injury (Fig. 1).
Generally, patients prefer FUE to FUSS for obtaining
donor hair, although the follicle survival rate remains con-
troversial because of less postoperative pain and to avoid
linear donor scar.3
Table 1. Comparative Analysis of FUE-extracted Grafts
Using a Loupe and Microscope
Minimum Maximum Average
TR (%) 1.3 17.3 7.40
Paring 0 17 4.31
Fracture 0 4 1.90
DP injury 0 3 0.52
Hair bulb partial
0 3 0.43
Telogen 0 22 9.21
Microscope TR (%) 1.3 15.89 6.34
Paring 2 20 9.07
Fracture 0 4 1.95
DP injury 0 4 0.79
Hair bulb partial
0 7 1.24
Telogen 3 37 16.62
TR = transected hair follicle/total number of hair follicles harvested. Paring,
fracture, DP injury, and hair bulb injury: number of hair follicles found with
each injury per 100 follicles. Telogen: number of telogen hair follicles found
per 100 grafts.
Park and You • Types of Minor Trauma to Hair Follicles During FUE
Despite the fact that FUSS can have phenomenal re-
sults with respect to minimal scarring when the tricho-
phytic closure strategy is used, this is a beneﬁt generally
seen from the doctor’s point of view and may differ from
the patient’s perspective. From the patient’s point of view,
FUE is a more minimally invasive and patient-friendly
Regardless, successful and consistent results of FUE
are still being demanded. The type of surgery that would
be considered a successful FUE surgery remains unclear.
When comparing FUE with FUSS, the TR and calculated
density are often compared, and the TR is often examined
by itself.5–7 The TR is undoubtedly a very important fac-
tor that must be considered during surgery, but a lower
TR in association with a high follicle survival rate is also
an imperative factor to be considered. Fewer studies have
evaluated the follicle survival rate in FUE. Beehner8 per-
formed FUE and FUSS simultaneously in the same patient
and reported an 85.2% follicle survival rate in FUSS and a
53.9% follicle survival rate in FUE.
Many researchers and hair surgeons believe that the
reason for the difference in the survival rate between FUE
and FUSS is the difference in the amount of perifollicu-
lar tissue between the 2 types of grafts. A thicker graft is
associated with a higher follicle survival rate; this fact is
recognized as the most basic concept of hair transplanta-
tion. Many other factors may also affect the follicle sur-
vival rate, such as the out-of-body time, dryness, physical
trauma, and surgeon’s implantation skills.9
In the present study, no paring, fracture, DP injury, or
bulb damage was observed while afﬁrming the randomly
selected follicles under a microscope; all of these follicles
were arbitrarily acquired by FUSS and analyzed as a fol-
licular unit by a highly experienced surgical assistant.
How speciﬁcally and practically hair follicle trauma af-
fects the survival rate remains unknown. However, based
on our literature review, it is possible to infer that the mi-
nor trauma described in this report has more negative
effects on hair follicles than intact and perfectly condi-
tioned grafts with no minor trauma.
Fig. 1. Various types of follicle injury that are likely to occur during FUE (×60 magnication). A, Total transection. B, Partial transection. C,
Paring. D, DP injury. E, Bulb injury. F, Fracture. G, Telogen.
PRS Global Open • 2017
Hair follicle stem cells are not a single multipotent
entity given that a pilosebaceous unit contains numerous
stem cell populations and subpopulations ranging from
epithelial to mesenchymal and melanocyte stem cells. The
epithelium comprises the hair shaft, inner root sheath,
and outer root sheath (ORS). The isthmus is the region
between the entry of the sebaceous duct and the inser-
tion of the arrector pili muscle. The isthmus includes the
“bulge” region (otherwise known as the basal, outermost
ORS layer of the distal hair follicle epithelium at the prox-
imal end of the isthmus), which contains the epithelial
hair follicle stem cells. The DP and dermal sheath of the
follicle are mesenchymal in origin and have been shown
to harbor multipotent stem cell subpopulations distinct
from epithelial hair follicle stem cells, such as skin-derived
precursors, NESTIN+ cells, or SOX2+ cells.10–12
Hair follicle morphogenesis and regeneration depend
on intensive but well-orchestrated interactions between
epithelial (bulge stem cells, their descendent secondary
hair germ cells, and hair matrix cells) and mesenchymal
(DP and dermal sheath) components.10–13 Thus, both DP
stem cells and epithelial stem cells are important, and hair
growth is reportedly degraded if either is missing.
Each type of trauma described in this study is shown in
detail in Figure 1. First and foremost is transection, which
can occur not only during the strip incision process of
FUSS but also during dissection in FUE. The transected
donor hair follicle obtained by FUE remains in the donor
scalp tissue; in FUSS, however, it completely dissipates.
The second type of injury is paring. Paring refers to lac-
eration or avulsion of the ORS by the punch tip (Fig. 2).14
The third injury is fracture. A fracture is deﬁned as
separation of either end of the hair follicle into 2 or more
pieces due to stress at some point along the length of the
follicle.14 The cause of a fracture is rotation of the punch
tip, which partially traumatizes the hair follicle like a lac-
eration, resulting in injury to the ORS and the hair shaft
on one side; the ORS and partial hair shaft on the other
side remain intact, maintaining the overall continuity of
the follicle (Fig. 2). Theoretically, fractures occur more
frequently under circumstances of increased axial force
such as rubbery skin; long, thick hair follicles; hyperelastic
skin; and use of a blunt punch tip.15
The fourth type of trauma is DP injury. This occurs
due to an insufﬁcient punching depth when considering
the adhesion between the perifollicular tissue and the
hair follicle. When the depth is too superﬁcial for extrac-
tion, the tissues of the ORS encompassing the hair bulb
and DP can likewise be detached or torn out. Therefore,
from a clinical perspective, when conducting the extrac-
tion, the surrounding scalp tissues can be elevated by tag-
ging along the graft, which can suddenly break off later,
resulting in frequent DP injuries. If the punch tip enters
even deeper than the minimal punching depth, it can
reach a segment where extraction of the hair follicles can
be conducted in a smoother, easier manner without hav-
ing to increase the TR. The authors refer to this as the
safe punching depth.
The ﬁfth type of trauma is bulb partial damage. This
is another very important factor that may be overlooked.
A partially damaged hair follicle will be considered intact
if it does not contribute to the TR, which we have recog-
nized. However, it is highly likely to affect the survival rate.
An important fact that matters in the present study is that
such types of damage to the hair bulb frequently occur
in many cases and that they can usually be visualized only
under a ×60 magnifying microscope and not through a
×5 to ×6 magnifying loupe, which is routinely used during
FUE. Trauma to the hair bulb such as damage, crushing,
or partial avulsion are thought to profoundly affect the
survival of hair follicles. From a comprehensive viewpoint,
not only are a too superﬁcial punching depth and inad-
equate extraction undesirable, but a too deep punching
depth should be avoided as well.
Fig. 2. Concept schema for easy understanding of paring, fracture, and transection.
Park and You • Types of Minor Trauma to Hair Follicles During FUE
The main limitation of this study is that transection
and other types of minor trauma were dependent upon
the operators’ skill levels and variations in techniques.
We consider that a further study is required to gain a
better understanding of the effects of various types of
trauma on the survival rate of damaged follicles. We also
believe that an additional study should be conducted to
determine how these types of trauma vary depending
on various FUE techniques and skin and hair charac-
This study conﬁrms the existence of diverse types of
damage to hair follicles obtained through FUE. Such graft
damage was less often detected by a ×5 to ×6 magnifying
loupe, which is routinely used during FUE, than with a
×60 microscope. The present study will serve as a baseline
for additional studies on this topic, enabling researchers
to discover better surgical techniques that ensure satisfac-
tory results for both the doctor and the patient.
Jae Hyun Park, MD, PhD
Dana Plastic Surgery Clinic
Samju Building 10F
Gangnamdaero 606, Gangnam-gu
1. Rassman WR, Bernstein RM, McClellan R, et al. Follicular unit
extraction: minimally invasive surgery for hair transplantation.
Dermatol Surg. 2002;28:720–728.
2. Beehner M. A comparative study of FUE and FUT survival in four
patients. 23rd Annual Scientiﬁc Meeting, ISHRS, Chicago, 2015.
3. Harris JA. Follicular unit extraction. Facial Plast Surg Clin North
4. Dua A, Dua K. Follicular unit extraction hair transplant. J Cutan
Aesthet Surg. 2010;3:76–81.
5. Ors S, Ozkose M, Ors S. Follicular unit extraction hair transplan-
tation with micromotor: eight years experience. Aesthetic Plast
6. Shin JW, Kwon SH, Kim SA, et al. Characteristics of roboti-
cally harvested hair follicles in Koreans. J Am Acad Dermatol.
7. Cole J. Status of individual follicular group harvesting. Hair
Tranplant Forum Int’l. 2009;19:20–24.
8. Beehner M. MFU grafts and strip harvesting – we hardly know
yet. Hair Transplant Forum Int’l. 2014;24:125–126.
9. Parsley WM, Perez-Meza D. Review of factors affecting the growth
and survival of follicular grafts. J Cutan Aesthet Surg. 2010;3:69–75.
10. Ohyama M, Veraitch O. Strategies to enhance epithelial-mes-
enchymal interactions for human hair follicle bioengineering.
J Dermatol Sci. 2013;70:78–87.
11. Ohyama M, Zheng Y, Paus R, et al. The mesenchymal component
of hair follicle neogenesis: background, methods and molecular
characterization. Exp Dermatol. 2010;19:89–99.
12. Commo S, Gaillard O, Bernard BA. The human hair follicle
contains two distinct K19 positive compartments in the out-
er root sheath: a unifying hypothesis for stem cell reservoir?
13. Yang CC, Cotsarelis G. Review of hair follicle dermal cells.
J Dermatol Sci. 2010;57:2–11.
14. Lorenzo J, Devorye JM, True RH, et al. Standardization of the
terminology used in FUE: part I. Hair Transplant Forum Int’l.
15. Cole JP. An analysis of follicular punches, mechanics, and dy-
namics in follicular unit extraction. Facial Plast Surg Clin North