Australasian Journal of Dermatology (2003) 44, 10–18
PERSONAL REVI EW
Methods of evaluating hair growth
Alexander J Chamberlain and Rodney PR Dawber
Department of Dermatology, Churchill Hospital, Headington, Oxford, United Kingdom
over the last two decades would have occurred at all.
SUM MARY Although sophisticated computerized techniques pioneered
by the wool industry are now available to quantify the
For decades, scientists and clinicians have examined various parameters of hair growth, the intrinsic complexity
methods of measuring scalp hair growth. With the of hair growth itself has been the main obstacle to the
development of drugs that stem or even reverse the development of simple ofﬁce-based assessment tools. The
miniaturization of androgenetic alopecia, there has aim of this review is to outline the various methods available
been a greater need for reliable, economical and for the measurement of hair growth, their limitations and
minimally invasive means of measuring hair growth their value to the clinician.
and, speciﬁcally, response to therapy. We review the
various methods of measurement described to date,
THE HAIR CYCLE
their limitations and value to the clinician. In our
opinion, the potential of computer-assisted technology Much of our understanding of hair growth is based on
in this ﬁeld is yet to be maximized and the currently animal studies.1 The dynamics of the hair cycle not only
available tools are less than ideal. The most valuable differ between species and race but also with age, gender,
means of measurement at the present time are global body site and across seasons. Physiological or pathological
photography and phototrichogram-based techniques states such as pregnancy, malnutrition or malignancy can
(with digital image analysis) such as the ‘TrichoScan’. also modulate hair growth. The total number of follicular
Subjective scoring systems are also of value in the units on the human scalp is approximately 100 000–150 000
overall assessment of response to therapy and these and it is generally accepted that this number is ﬁxed and
are under-utilized and merit further reﬁnement. does not increase. These follicles are quite evenly distributed
over the scalp and most typically in groups of three. Although
Key words: androgenetic alopecia, epiluminescence
these small groups grow in phase, the growth of scalp hair
microscopy, phototrichogram, scalp photography,
on the whole is asynchronous or mosaic. Hair follicles
undergo active growth (anagen) in a cyclic fashion, with this
phase typically lasting 3–7 years on the scalp vertex. Anagen
has traditionally been divided into six stages of development,
from the onset of mitotic activity within the secondary hair
INTRODUCTION germ (anagen-I) to the fully developed follicle that ﬁrst
Many methods of evaluating the growth of hair have been emerges beyond the skin surface (anagen-VI). After a brief
described by both scientists and clinicians alike. While the transitional phase (catagen) hairs enter a resting phase
majority of these methods have been developed to progress (telogen) lasting weeks before being shed. This process then
the understanding of normal hair physiology, the discovery repeats itself over and over. At any one time, 85–90% of scalp
of agents that promote hair growth has necessitated the hairs are in anagen, with the majority of the remainder in
development of reliable and reproducible means of assessing telogen. The growth rate of the hair follicle is fairly constant,
hair loss and monitoring response to therapy. Indeed, the averaging about 0.5 mm per day on the scalp vertex and a
majority of techniques developed to date have followed the little less at the margins.
discovery of minoxidil and its application in androgenetic
alopecia (AGA). Without this revolution, it is unlikely that DIMENSIONS OF HAIR GROWTH
much of the intense hair growth research and innovation
It is important to deﬁne the dimensions that constitute hair
growth before one can begin to interpret the various methods
of its measurement. The basic biological parameters of hair
Correspondence: Dr Alexander J Chamberlain, Clinical Research growth include rate of linear growth, hair shaft diameter,
Fellow, Department of Dermatology, Churchill Hospital, Old Road,
hair density and hair-cycle status. The anagen : telogen ratio
Headington, Oxford OX3 7LJ, UK.
Email: firstname.lastname@example.org (or percentage of anagen-VI hairs) is the best measure of
Alexander J Chamberlain, MB BS. Rodney PR Dawber, FRCP. cycle status given the impracticalities of measuring the
Submitted 27 March 2002; accepted 15 August 2002. duration of anagen, which relies on long periods of
Methods of evaluating hair growth 11
observation and identiﬁcation of individual hairs. Pigment growth in men with AGA been developed.2 This question-
content must also be considered a variable of some biological naire was developed in the Merck Research Laboratories and
signiﬁcance in the study of alopecia. has already been used to supplement clinical measures in
It is crucial to recognize that the parameters of hair growth trials examining the effects of ﬁnasteride.3 The questionnaire
that are of major interest to the scientist are different to those consists of ﬁve questions that address patient perceptions of
of the clinician or the patient. While much of the recent hair growth and satisfaction with hair appearance. The
scientiﬁc research in this area has concentrated on the scores have been shown to correlate with hair counts, albeit
mechanisms that control the activity of putative follicular modestly. This subjective measure is probably a useful
stem cells, the parameters more likely to be of value to adjunct in the assessment of response to therapy. While this
clinicians are diameter, density and cycle status. In contrast, questionnaire was designed to assess the perceptions of men,
the primary concern of the patient is reduction in density, it would not be difﬁcult to adapt this so that it were applicable
which is frequently expressed as ‘loss of body’. The patient to women also.
who is losing hair may also report an increase in shedding The manual collection, counting and weighing of hairs
(‘hair is falling out’), a reduction in growth rate (‘hair doesn’t shed on a daily basis is a simple technique that can be used
need cutting as often’), or a reduction in diameter (‘hair is to follow the progression of hair loss.4 Studies of this type
ﬁner’). Of course, the presentation of AGA is quite different have estimated that the average number of hairs shed daily
in women and men. Unlike a woman with diffuse hair loss is about 100, a ﬁgure that appears widely in hair literature
in whom the diagnosis may not be immediately clear, a man and is probably an overestimate for healthy young adults.
presenting with a patterned alopecia is usually all too This crude method is not only extremely tedious but requires
familiar with ‘common baldness’ and presents requesting careful standardization of collection technique and hair care.
treatment rather than a diagnosis. Hydration and seborrhoea are factors that affect hair weight,
At present, there is no ‘gold standard’ in the area of so these must also be standardized if this technique is to be
measurement of hair growth. The ideal measure would be applied in clinical trials.
non-invasive, simple to perform, reproducible, economical, There are a number of grading scales that exist for the
and able to integrate all of the basic biological parameters of classiﬁcation of AGA. It was Hamilton in 1951 who ﬁrst
hair growth as well as to provide information that is subdivided the patterning seen in men with AGA into types
meaningful to the patient. The vast majority of the methods I–VIII on a visual scale.5 This system of classiﬁcation was
of measurement that will be discussed here have been later modiﬁed by Norwood in 1975 who added four further
studied in AGA. intermediate grades: IIIa, III vertex, IVa and Va.6 Although
These methods of measurement are equally applicable to the Norwood–Hamilton scale has been used extensively in
other non-scarring alopecias, with the exception of patchy clinical trial evaluation, this system is too crude to reliably
alopecia areata, in which areas of hair loss are well-deﬁned document response to therapy. In reality, the progression of
and regrowth is easily identiﬁed; therefore accurate AGA or indeed regrowth with therapy occurs over a con-
measurement is not as crucial to the clinician. In scarring tinuum rather than in a stepwise manner. This scale prob-
alopecias, histology is vital for diagnosis but quantitative ably still has a role in the broader classiﬁcation of severity of
estimates of hair loss are again not as important. In both AGA in men, particularly in the identiﬁcation of those who
alopecia areata and scarring alopecia, clinical examination are more likely to respond to therapy.
and global photography provide the information of greatest In 1977, Ludwig proposed a grading scale for women with
relevance, although a more detailed discussion of this issue AGA.7 He suggested types I–III that represented a range of
can be found elsewhere and is beyond the scope of this diffuse alopecia over the crown in the so-called ‘female
review. The ideal frequency of measurement in the monitor- pattern’ that spares the frontal hair line. It is well recognized
ing of hair growth in response to therapy is another factor in that a certain percentage of women develop AGA in the ‘male
the equation that is yet to be established. On the basis of pattern’, particularly postmenopausal women.8
telogen duration, many clinical trials have chosen to Savin has expanded on the original grading systems with
measure response to therapy at 4-monthly intervals, and his pattern and density scales for classifying AGA in both
this is probably the minimum interval at which changes men and women (Fig. 1).9 In men, the appearance of the
may be detected. As any expected changes in hair thinning frontal scalp, mid area and vertex are ranked
parameters will be small if at all, it is probably prudent to F1–F6, M1–M5 and V1–V7, respectively. Female-pattern AGA
assess at 6–12-monthly intervals until a trend has been is divided according to the width of the central part. Density
established. The various methods of measurement of hair in both sexes is also graded on the basis of the part (D1–D8).
growth have been previously divided into non-invasive, Unfortunately, these qualitative systems are too crude to use
semi-invasive and invasive categories and this is a logical in clinical trials for anything more than deﬁning the base-
division that we have also chosen to structure our discussion line. They probably have a role in ofﬁce-based measurement
around. until more sensitive tools are widely available and they are
certainly signiﬁcant from a historical perspective.
Photography is a very important tool in the clinical
measurement of hair and its dynamics. Global photographs
Only recently has a validated and standardized question- of the scalp are clinically relevant in the assessment of AGA
naire aimed at the detection of subjective changes in hair because they represent an accurate record of the cosmetic
12 AJ Chamberlain and RPR Dawber
state of the patient. High-quality photographic systems with vertex views were used in the early ﬁnasteride trials (Fig. 2).3
stereotactic positioning devices for accurate patient position- It is our opinion that global photographs are a valid method
ing are now available commercially.10 Factors such as of hair measurement in the clinical setting, although the best
precise combing and lighting are critical to the repro- results are probably obtained in the hands of trained medical
ducibility of scalp photographs. The Canﬁeld technique has photographers.
recently been validated in a randomized controlled trial In recent years, epiluminescence microscopy (ELM) has
examining men with Hamilton III or IV AGA receiving oral been cleverly adapted to quantify hair growth. Epilumines-
ﬁnasteride or placebo.11 Four standard global views (vertex, cence microscopy is a clinical tool that was originally reﬁned
midline, frontal and temporal) are advocated, although only for the diagnosis of pigmented skin lesions, in particular the
early detection of melanoma. An European group has
created a scoring system based on hair density and diameter
as assessed by macrophotographs of a midline part at the
vertex of men with AGA (Fig. 3).12 These are performed
using a commercially available camera (Dermaphot; Heine
Optotechnik, Herrsching, Germany) designed for ELM with
4 magniﬁcation. An area measuring 14 13 mm is used to
base the measurements. Density is graded on a scale of 1
(fewer than four hairs) to 6 (more than 40 hairs) and dia-
meter is graded as 1 (thin), 2 (medium) or 3 (thick). A
separate hair diameter diversity scale is graded 0 (<20% in
hair diameter diversity) or 1 (>20% hair diameter diversity).
They propose that a score of >20% diversity in hair diameter
is a useful clinical sign reﬂecting miniaturization. This is
therefore of potential use in the diagnosis of AGA, but prob-
ably too crude for monitoring change. Their density and
diameter scale has been shown to correlate well with the
Hamilton classiﬁcation and histological hair density. In some
ways it can be considered an adaptation of the Savin scale,
but localized to a precise point on the vertex and under
magniﬁcation. A key issue to consider is whether a postage
stamp-sized area of scalp vertex is representative of the
global effects of AGA on the scalp. Even if it is, this technique
is still qualitative and quite subjective, but easy to perform
Figure 2 Schematic representation of stereotactic scalp photo-
graphy demonstrating fixation of the subject on a brow and chin rest
Figure 1 Pattern and density Savin scales. with the camera mounted on a rotating arm.
Methods of evaluating hair growth 13
The information technology revolution of the late twen- were hair styling and combing, camera-to-scalp distance and
tieth century has resulted in advances throughout medicine, contrast between scalp and hair colour. These are short-
including hair measurement. The major capability of the comings that the Canﬁeld system has partly addressed
computer that has been exploited in the ﬁeld of hair with standardized combing and patient positioning, although
measurement is image analysis and its quantiﬁcation of the contrast between scalp and hair colour, particularly
clinical or even histological appearances. High-speed when it is minimal, is a limitation common to all imaging
processing, high-resolution imaging and vast storage cap- systems.
acity for archiving are further advantages of computer
systems in clinical measurement. A computer-assisted
method of estimating hair density has been used to
estimate the response to therapy in a patient with diffuse The linear growth rate of scalp hair can be measured in a
alopecia areata.13 This involves the digitization of a photo- number of ways. Perhaps the simplest technique is to stain a
graphic image of the scalp and could equally be applied to group of hairs using a dye that contrasts with the colour of
AGA. Darker shades of grey are interpreted as hair and the native hairs.14 A growth rate can then be calculated by
lighter shades as scalp and then the proportion of each dividing the length of unstained hair in millimetres by the
variable is calculated. Factors that inﬂuenced the results number of days between measurements (mm/day). If
Figure 3 Scoring system of hair
density and shaft diameter using a
magnified photographic scale (repro-
duced with permission from Arch.
Dermatol. 2001; 137: 641–6, copy-
righted 2001, American Medical
14 AJ Chamberlain and RPR Dawber
estimated over a standardized area, the proportion of anagen This involved shaving a small area of scalp hair as well as
and telogen hairs can also be assessed, because only the plucking 50–100 hairs using forceps without sharp edges and
anagen hairs will show growth. Close-up photography ideally covered with adhesive tape (Fig. 5). The shaved area
improves the accuracy of such observations, although con- was examined after 10 days to assess the linear growth rate.
ditions must be strictly standardized and there must be The roots of the plucked hairs were examined to provide an
sufﬁcient contrast between background scalp and hair estimate of cycle status (anagen : telogen differential) and
colour.15 density was assessed using a microscope with 60 magniﬁ-
Alternatively, hairs may be clipped close to the surface, cation and an eyepiece marked with a 1-cm 2 area. Hair
shaved or even plucked prior to measuring growth rate, diameter was also assessed microscopically. Originally, hairs
although plucking results in a variable delay before the were graded into thick (0.1 mm), medium (0.05 mm) and
appearance of a new anagen hair. A designated area can be thin (0.025 mm) categories using calibrated wires for
re-clipped, shaved or plucked and then weighed after a set comparison. A ﬁnal parameter was the ‘regeneration period
period to measure regrowth. This technique has been used 90’, which was the time lag in the appearance of 90% of
to document normal growth,16 and response to minoxidil in plucked hairs from a given area. This technique was applied
women17 and ﬁnasteride in men18 with AGA. It has been extensively thereafter to study the hair of subjects of varying
proposed that the total weight of hair from a deﬁned area of ages and under various physiological inﬂuences.23 While this
scalp is an ideal quantitative measure of hair growth for use work helped to deﬁne the normal variations according to
in clinical trials.17 However, this technique seems just as age, gender and body site, it is now largely outdated as a
complex and tedious as other manual methods, requiring research technique in AGA. A further reﬁnement on the
careful degreasing, drying and control of humidity to avoid trichogram was the unit area trichogram (UAT), which
error. introduced a standardized pre-sampling, washing and
Calibrated capillary tubes have also been used to measure combing protocol, and plucking of hairs from within a
linear growth rate.19 These are ﬁtted around individual hairs deﬁned area (usually 35–44 mm2) to determine density in a
that have been clipped and then pressed gently against the more accurate fashion.24 The major shortfall of the
skin surface (Fig. 4). Measurements are daily or even more trichogram is that hairs in early anagen and vellus hairs are
frequently. Reference points would clearly be necessary if easily missed in a standard pluck because of their small size.
particular hairs were to be followed individually over time. Furthermore, plucking 50–100 hairs is quite a painful pro-
Intradermal injection of radiolabelled substances followed cedure for patients to undergo. Plucking is also known to
by autoradiography is a research technique that provides an change the natural course of the hair cycle.25
accurate method of marking hairs along their length. 20 The ﬁrst efforts to document the growth of hair using
Linear growth rate can then be measured by dividing the photography at close range were performed on three
distance between marks on autoradiographs by the time Japanese men who were studied at regular intervals over a
between injections. The small doses of radiation required in period of 2 years.15 Hairs at different body sites including the
these assays have been deemed safe in non-pregnant scalp were studied, enabling estimates of the lengths of
humans. These techniques are not only labour-intensive but anagen and telogen for each individual. Hairs were kept
serial scalp injections are unlikely to be well tolerated by clipped at lengths of 1 mm (whenever photographed) within
patients outside a research setting. Linear growth rate is not a small area to allow accurate identiﬁcation of individual
a vital parameter in the measurement of miniaturization. hairs.
In the 1960s a compound measurement of the major
biological parameters of hair growth was ﬁrst described.21
This technique was to be known later as the trichogram.22
Figure 4 Hair-growth measurement using graduated scale
capillary tubes. Figure 5 Technique for plucking hairs with surgical forceps.
Methods of evaluating hair growth 15
This work formed the scientiﬁc basis of the photo- growth. Cells arrested in metaphase are expressed as a
trichogram (PTG) that has been reﬁned by several investi- proportion of the entire matrix. This technique has mainly
gators.26,27 This technique involves serial magniﬁed been applied to the study of the seasonal variations in wool
photographs (Fig. 6) of a target area of scalp hair (1 cm2) over growth.38 However, this also involves administration of
a period of days to deﬁne which hairs are in anagen (those cytotoxics.
growing) and which are in telogen (those not growing). In Histopathological analysis of scalp biopsies has been used
addition to cycle status, the PTG enables measurement of for some time now to investigate hair growth. Biopsies are
linear growth rate as well as diameter and density. Although performed under local anaesthesia. A 4- or 6-mm punch
painless, it is time-consuming and is limited by the same deep into the subcutaneous tissue directed along the slant of
inherent problem as other scalp imaging systems of exiting hairs is typically taken from a transitional area
differentiating hairs from scalp background. The application between balding and normal scalp and a suture is normally
of an immersion oil28 and temporary hair dye29 have required for haemostasis. Although the original descriptions
improved this contrast to some degree. Several investigators of this technique involved a single punch, it is more usual to
have attempted to automate the process of monitoring hair take two punches at the present time. Early studies of
growth via PTG, although overlapping hairs and various macaque monkeys (who develop AGA) using scalp biopsies
artefacts have proven to be major obstacles to computerized sectioned vertically along the length of the hair follicle
measurement.27,30,31 Assessment of hair diameter is also enabled the construction of histograms known as ‘folliculo-
unreliable unless magniﬁcations in the order of 20 are grams’.39 These depicted follicle lengths and proportions of
used.32 A computer-assisted image analyzer has been shown anagen, catagen and telogen hairs, and over time were able
to enhance the quality and reliability of this facet of to demonstrate the improvement in the terminal : vellus ratio
measurement.33 with minoxidil therapy.40
Despite these shortfalls, the PTG has been applied success- It has since been shown that horizontal sectioning
fully in ﬁnasteride trials to show statistically signiﬁcant provides greater diagnostic information than vertical sec-
increases in density and the anagen : telogen ratio over tions alone.41 This mode of processing provides measures of
12 months in men with AGA.3,34 Increases in hair diameter density, hair-shaft diameter, and the anagen : telogen and
have not been able to be adequately documented in these terminal : vellus ratios. Automated computer analysis has
trials using the PTG. been successfully adapted to assist with the quantiﬁcation of
The latest modiﬁcation of the PTG combines ELM with these parameters.42 Both density and terminal : vellus ratios
digital image analysis; the ‘TrichoScan’.35 In comparison to have been shown to be useful indices in monitoring the
the traditional PTG, this method uses ELM instead of response of AGA to minoxidil43 and ﬁnasteride,44 respec-
macrophotography, as well as contrast enhancement of hairs tively. A terminal : vellus ratio of less than 4:1 has been
with temporary dye. Specially developed computer software suggested as diagnostic of AGA, whereas the ratio in the
enables assessment of the four basic biological parameters of
hair growth (Fig. 7), with the whole procedure taking
20 min. This technique has already been used to document
increases in hair count and cumulative diameter in men with
AGA treated with ﬁnasteride, over a period of 6 months. The
developers of the TrichoScan appear to have drawn on years
of PTG research to create a validated clinic-based measure-
ment tool that is both elegant and patient friendly. The cost
of equipping the clinic with this system is an important
The ultimate measure of hair growth is the examination of
matrix cell kinetics. The two main proliferative indices are
the mitotic index and the labelling index.36 The former is a
count of the number of actively dividing cells at a given point
in time, as measured on wax-embedded sections. The latter
is a count of the number of cells entering mitosis during a
given period, and requires intradermal injections of tritiated
thymidine prior to biopsies subjected to light microscopy
autoradiography at set intervals.37 These indices are not only
invasive, but they only provide a static appreciation of a
dynamic process. In addition, thymidine is potentially toxic
and therefore unsuitable for repeated administration. The
metaphase index, in contrast, provides a measure of the rate
of cell production and is more suitable for studying hair Figure 6 Macrophotograph of scalp hair.
16 AJ Chamberlain and RPR Dawber
normal scalp is between 6:1 and 8:1.43 One of the criticisms manner does not appear to be available at the present
of this method is that horizontal sections taken at the level of time, despite the intense research into this subject. The
the entry of the sebaceous duct will underestimate the total large variety of techniques employed over the decades is
number of vellus hairs because many of these are found testament to this conclusion. The ideal tool(s) would be
more superﬁcially in the midreticular dermis. 38 able to measure hair-shaft diameter and hair density at a
Another histological parameter that has been studied is the microscopic level, in addition to providing a subjective
volume of the hair bulb. In animal studies the volume of the assessment of both the appearance and satisfaction of the
dermal papilla has been shown to bear a direct relationship patient.
to the volume of terminal hair.45 Although this work has been While the UAT and the PTG may be the favoured tools
replicated in humans with AGA,46 this parameter has not within the setting of clinical trials, we feel that subjective
been used to follow the response of AGA to therapy. scores and global photography are of greater relevance in the
The major limitation of these invasive methods in the clinic. A subjective scoring system for women with AGA or
study of hair growth is that they do not permit the repeated even a unisex scoring system are yet to be developed and
sampling of a consistent area of scalp over time. Further- validated as far as we are aware. In our opinion, the method
more, a single 4-mm sample of scalp is not always that shows the greatest promise in the monitoring of AGA
adequately representative of the global process because of and its response to therapy is the TrichoScan, although this
regional variation.47 is only likely to be ﬁnancially viable for academic depart-
ments (as opposed to the average clinician) at the present
time. While the impact of computer-assisted image analysis
has been largely disappointing as far as progressing
An adequate means of measuring hair growth in the clinic techniques of hair measurement, we hope that the next
over time in a reproducible, economical and non-invasive decade will see the introduction of improved means of
Figure 7 Software interface depicting variables of hair growth as measured by the ‘Trichoscan’ technique (reproduced with permission from
Eur. J. Dermatol. 2001; 11: 362–8).
Methods of evaluating hair growth 17
assessing patients with AGA, ideally adaptable for other 19. Saitoh M, Uzuka M, Sakamoto M. Rate of hair growth. In:
disorders of hair growth. Montagna W, Dobson RL (eds). Advances in Biology of the Skin,
Vol. IX. Oxford: Pergamon Press, 1969; 183–201.
20. Munro DD. Hair growth measurement using intradermal
sulphur-35 cystine. Arch. Dermatol. 1966; 93: 119–22.
ACKNOWLEDGEMENTS 21. Barman JM, Pecoraro V, Astore I. Method, technique and
Dr Chamberlain was the recipient of the 2001 Novartis computations in the study of the trophic state of human scalp
hair. J. Invest. Dermatol. 1964; 42: 421–6.
Travelling Fellowship and wishes to gratefully acknowledge
22. Barman JM, Astore I, Pecoraro V. The normal trichogram of the
Novartis Australia and the Australasian College of Derma- adult. J. Invest. Dermatol. 1965; 44: 233–6.
tologists for their support. We also wish to thank Oxford 23. Pecoraro V, Astore IPL. Measurement of hair growth under
Medical Illustration at the John Radcliffe Hospital for their physiological conditions. In: Orfanos CE, Happle R (eds). Hair
technical assistance with the artwork. Diseases. Berlin: Springer-Verlag, 1989; 237–54.
24. Rushton H, James KC, Mortimer CH. The unit area trichogram
in the assessment of androgen-dependent alopecia. Br. J.
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