Cosmetics 2015, 2, 384-393; doi:10.3390/cosmetics2040384
The Scalp Has a Lower Stratum Corneum Function with
a Lower Sensory Input than Other Areas of the Skin Evaluated
by the Electrical Current Perception Threshold
Yutaka Takagi *, Hiroko Takatoku, Hiroyuki Terazaki, Tadashi Nakamura, Koichi Ishida and
Kao Corporation, R&D, 2-1-3 Bunka, Sumida-ku, Tokyo 131-8501, Japan;
E-Mails: firstname.lastname@example.org (H.Ta.); email@example.com (H.T.);
firstname.lastname@example.org (T.N.); email@example.com (K.I.); firstname.lastname@example.org (T.K.)
* Author to whom correspondence should be addressed; E-Mail: email@example.com;
Tel.: +81-3-5630-9792; Fax: +81-3-5630-9330.
Academic Editor: Enzo Berardesca
Received: 30 September 2015 / Accepted: 17 November 2015 / Published: 20 November 2015
Abstract: Many people feel frequent prickling or itching sensations on their scalp.
The scalp is an atypical area of the skin since it is normally covered with thick hair and has
many sebaceous glands and sweat glands. The scalp often has skin problems that can affect
its sensitivity and functions. However, not much is known about stratum corneum function
and the neural sensitivity of the scalp. Here we evaluated stratum corneum function and the
neural sensitivity of the scalp of 47 normal male individuals in various skin conditions and
compared the results to that to the forehead. The neural sensitivity was evaluated by
measuring the electrical current perception threshold (CPT). The cutaneous barrier function
and stratum corneum moisture-retention ability (MRA) of the scalp were significantly
lower than on the forehead, even if there were some scalp problems. Depending on the
increase in severity of scalp skin problems, both these skin functional properties and the
CPT decreased significantly. However, regardless of its lower functional properties, scalp
skin was not significantly lower than that of the forehead. Although the scalp has a low
stratum corneum function compared with the forehead and has easily induced skin
problems, the scalp skin has less sensitive sensory nerves, resulting in experiencing a
worsening of scalp symptoms more easily.
Cosmetics 2015, 2 385
Keywords: scalp skin; stratum corneum; current perception threshold; forehead
The scalp is a peculiar type of skin that is normally covered with thick hair and has many sebaceous
glands and sweat glands. Those special circumstances may cause a prickling or itching feeling on the
scalp, which is felt very often by some subjects. We have found that about one-third of people worry
about these unpleasant feelings in Japan (data not shown). Furthermore, the scalp can have many
additional problems, such as dandruff, odor, and so on. To take care of the scalp and hair, many hair
care products, such as shampoos, hair conditioners, hair styling products, and drugs, are used almost
daily. There are many reports about dandruff [1–4]. Bin Saif reviewed scalp pruritus, the nerves on
hair follicle and hair, and mediators and receptors involved in the itchy sensation . However, there
are few reports about the stratum corneum functions [4–7] or the sensitivity of the scalp [8–12]
compared with skin at other body regions. Furthermore, the evaluations of actual nerve reactions
compared with other body regions are very few. In this study, we analyzed the skin’s functional
properties and the neural sensitivity of the scalp. The electrical current perception threshold (CPT) of
sensory nerves measured with a Neurometer
has been used to demonstrate abnormalities in
neuropathic conditions [13–15] and also to evaluate sensitive skin . The sensitivity of the scalp to
electric stimulation using a Neurometer
was compared to the forehead of each subject. Furthermore,
we analyzed the relationship between skin properties and neural sensitivity and various scalp
conditions, such as erythema, scaling, papules, and so on. From these analyses we found that the scalp
has a low stratum corneum function compared with the forehead and has easily induced skin problems;
however, the scalp skin has fewer sensitive sensory nerves, resulting in experiencing a worsening of
scalp symptoms more easily.
2. Experimental Section
2.1. Study Design
The present study adhered to the tenets of the Declaration of Helsinki. All clinical studies were
reviewed and approved by the Review Board of the Kao Corporation (Tokyo, Japan) and formal
informed consent was obtained from each subject before the study.
Healthy male subjects were recruited randomly and 47 male volunteers participated in this study.
Subjects with alopecia areata, severe scalp eczema, and/or severe dandruff were excluded.
2.3. Test Procedure
Each subject washed his head and face on the eve of the evaluation day. Following this washing,
topical application of skin care products on the analyzed areas was prohibited until after the skin
Cosmetics 2015, 2 386
evaluation. Both sides of the head (a 5 mm × 5 mm area 5 to 7 cm above the ear) were used for the
evaluation. The hairs of the evaluated areas were removed by scissors immediately before the
evaluation. Sebum levels on the forehead and the scalp were analyzed with a Sebusheet
(Asahi Techno Lab. Ltd., Kanagawa, Japan) according to seven grades (0, 25, 50, 75, 100, 150, and
). A TPX-90 Handy PH meter (Tokyo Glass Kikai Ltd., Tokyo, Japan) was used with a flat
glass electrode according to EEMCO guidance . The average value of three measurements was used
for analysis. The CPT was measured with an electric current sine wave stimulator of sensory nerves
CPT/C, Neurotron Inc., Baltimore, MD, USA). Three sine wave stimulations (at 2000,
250, and 5 Hz) produced by the Neurometer
provided selective simulations for three subsets of nerve
fibers . Following these measurements, the head and forehead of each subject was washed with a
cleanser and dried by a specialist. After acclimation at 20 ± 2 °C, 40% ± 5% humidity for 20 min,
transepidermal water loss (TEWL) and stratum corneum moisture-retention ability (MRA) were
measured with a Tewameter TM210
(Courage + Khazaka electronic GmbH, Cologne, Germany) and
CM825 (Courage + Khazaka electronic GmbH), respectively. Specialists who were
internally trained visually rated the scaling, erythema, papules, eschars, pustules, and nodules on a
scale of 0 to 4 (0 = none, 1 = slight, 2 = mild, 3 = moderate, and 4 = severe) on the evaluated areas of
2.4. Statistical Analysis
Data obtained from both sides of the head were calculated as averages. Differences between the
scalp and the forehead were determined statistically with Student’s paired t-test.
3.1. Participants with Skin Symptoms
Forty-seven males, aged 27 to 46 years old (36.1 ± 4.8, mean ± S.D.), were included in this
evaluation. All subjects had hair on the evaluated areas and none of them had severe scalp problems.
Their scalp conditions are summarized in Table 1.
Table 1. Scalp skin symptoms of subjects.
Score Scaling Erythema Papule Eschar Pustule Nodule
0 15 3 28 35 31 43
1 18 26 11 8 12 3
2 11 14 8 4 1 1
3 3 4 0 0 3 0
4 0 0 0 0 0 0
SUM 47 47 47 47 47 47
Cosmetics 2015, 2 387
3.2. Comparison of Measured Data between the Scalp and the Forehead
Prior to washing the scalp and the face, the sebum level of the scalp was more than 50% higher than
that of the forehead (scalp: 89 ± 29 μg/cm
, forehead: 59 ± 31 μg/cm
, p < 0.01, Figure 1A). However,
the average skin surface pH of the scalp was similar to that of the forehead (scalp: 4.80 ± 0.45,
forehead: 4.80 ± 0.40, Figure 1B).
Following washing with the cleanser, the MRA of the scalp was significantly lower than that of the
forehead (scalp: 34.5 ± 9.4, forehead: 54.3 ± 11.2, p < 0.01, Figure 1C) and the TEWL of the scalp was
significantly higher than that of the forehead (scalp: 6.6 ± 1.6 g/m
·hr, forehead: 5.5 ± 1.6 g/m
p < 0.01, Figure 1D).
Figure 1. Comparison of measured data for sebum level (A), skin surface pH (B), MRA (C),
and TEWL (D) between the scalp and the forehead. Each column indicates the average and
the bars show standard deviation. ** indicates p < 0.01 as a significant difference.
The CPT on the scalp and the forehead was measured with a Neurometer
prior to washing with the
cleanser. Although the MRA and TEWL of the scalp indicate that the scalp has a lower stratum
corneum function than the forehead, the scalp had a significantly higher CPT value than the forehead
Scalp Forehead Scalp Forehead
Cosmetics 2015, 2 388
Figure 2. Comparison of measured data for CPT for 2000 Hz (A), 250 Hz (B), and 5 Hz (C)
between the scalp and the forehead. Each column indicates the average and the bars show
standard deviation. * indicates p < 0.05 and ** indicates p < 0.01 as a significant difference.
3.3. Comparison of Measured Data between Scalps with Skin Symptoms of Different Severity
and the Forehead
The properties of the stratum corneum and the cutaneous sensitivity might be affected by the skin
symptoms. Thus, we analyzed the relationship between the stratum corneum properties and the
severity of skin symptoms (as shown in Table 1) and found that every skin symptom affected the
stratum corneum properties and the cutaneous sensitivity with the same tendency (data not shown).
Because of the low severity of each type of skin symptom, the subjects were classified into three
groups according to the severity of the scalp skin problem. Group I did not have any kind of skin
symptoms with a severity score of more than 1 (n = 21), Group II had one skin symptom with a
severity score of more than 1 (n = 12), and Group III had more than one skin symptom with a severity score
of more than 1 (n = 14).
Depending on the increase in the severity of scalp skin problems, the sebum level decreased
significantly, but even Group III had more sebum on the scalp than on the forehead (Figure 3A).
The skin surface pH was significantly higher with the increased severity of skin problems (Figure 3B).
The MRA of the scalp of Group I was significantly lower than that of the forehead and was dependent
on the increased severity of skin problems (Figure 3C). The TEWL of the scalp of Group I was
significantly higher than that of the forehead, but it was even higher in Groups II and III (Figure 3D).
CPT value （x10mA）
CPT value （x10mA）
CPT value （x10mA）
Cosmetics 2015, 2 389
Figure 3. Comparison of measured data for sebum level (A), skin surface pH (B), MRA (C),
and TEWL (D) between scalps with skin symptoms of different severity and the forehead.
Each column indicates the average and the bars show standard deviation.
* indicates p < 0.05, ** indicates p < 0.01 and *** indicates p < 0.001 as a significant
difference. NS indicates as no significant difference.
The CPT on the scalp of Group I was significantly higher than that of the forehead at each level of
current. Depending on the increased severity of skin problems, these values decreased significantly in
Groups II and III. Only the 2000 Hz current had a higher CPT value on the scalp of Group III than on
the forehead and there was no significant difference in the CPT value for 250 and 5 Hz, even in
Group II (Figure 4A–C).
Figure 4. Cont.
CPT value （x10mA）
CPT value （x10mA）
Cosmetics 2015, 2 390
Figure 4. Comparison of measured data for CPT for 2000 Hz (A), 250 Hz (B), and 5 Hz (C)
between scalps with different skin symptoms and the forehead. Each column indicates the
average and the bars show standard deviation. * indicates p < 0.05, ** indicates p < 0.01 and
*** indicates p < 0.001 as a significant difference. NS indicates as no significant difference.
Although scalp skin is less sensitive than other areas of skin, there is a high prevalence of pruritus.
Furthermore, the scalp easily develops other skin problems, not only pruritus but also dandruff, odor,
and itching, because it has many sweat glands and sebaceous glands and is usually covered with thick
hair. However, there are only a few reports about stratum corneum function on the scalp. O’goshi et al.
reported that the scalp has a significantly higher high-frequency conductance and a significantly lower
TEWL than the cheek . However, in our evaluation, the scalp has a significantly lower capacitance
and a significantly higher TEWL compared to the forehead. As the skin surface hydration of the cheek
is significantly lower than that of the forehead , it is presumed that both the scalp and the cheek
have a lower water-holding capacity compared to the forehead. The lower conductance of the cheek
might be caused by a low sebum level , but our evaluation showed that the scalp has significantly
more sebum compared to the forehead. In our evaluation, TEWL and MRA were measured following
skin washing with cleansers and this treatment might cause the different results between these
two evaluations. Additionally, the scalp conditions and hair affect these values, e.g., all subjects in our
evaluation had thick hair on the side of the head that was evaluated. Stratum corneum functions such
as TEWL and MRA are greatly affected by the existence of water such as sweat and sebum. The
amount of sweat and sebum are changes dependent on the subjects’ condition prior to the evaluation.
Thus, to standardize the condition, the stratum corneum functions were evaluated following washing
with cleanser and habituation in this evaluation.
Despite its low stratum corneum functions, the scalp has a higher CPT value which indicates that
the scalp is more sensorily obtuse compared to the forehead. Mori et al. reported that decreases in skin
surface hydration and increases in TEWL are correlated with the decrease in CPT on the forearm .
Also, Tominaga et al. reported that dry skin induced by acetone treatment had increased intraepidermal
nerve fibers in mice . The lower stratum corneum functions such as sensitive skin and atopic
dermatitis can easily cause the skin inflammation and pruritus. Moreover, the thicker epidermis 
and greater number of stratum corneum layers  of the scalp compared to the forehead may affect the
CPT value （x10mA）
Cosmetics 2015, 2 391
sensitivity. However, the scalp skin has less sensitive sensory nerves, even if the stratum corneum
functions are low, showing that the scalp is a very special property. The high humidity which leads to
sweat and sebum, resulting in a great deal of moisture on the stratum corneum, might be one reason
causing these less sensitive sensory nerve. Another evaluation indicated that the scalp is notably
insensitive to innocuous and noxious changes in temperature . Moreover, it was reported that scalp
skin is less sensitive to histamine-induced experimental itching compared to the forearm , although
the scalp was more sensitive to a sodium lauryl sulphate challenge than the forearm .
The CPT of sensory nerves measured with a Neurometer
has been used to demonstrate
abnormalities in neuropathic conditions [13–15]. Five Hz stimulates unmyelinated C fibers, resulting
in a slow pain described as “burning” or “stinging”, 250 Hz stimulates Ad fibers with a feeling of fast
pain and temperature, and 2000 Hz stimulates Ab fibers producing the sensations of touch and a more
In our evaluation, normal scalp skin was significantly less sensitive against all three of these
electrical stimuli compared to the forehead; these results agree well with the previous reports described
above. However, with increased skin problems and skin surface conditions, the scalp became more
sensitive, almost at the same level as the forehead in Group III, which has relatively severe scalp
problems, especially for 250 and 5 Hz stimuli.
The scalp has low stratum corneum functions even under conditions that readily induce skin
problems, such as high humidity and rich sebum levels which result in the existence of many microbes
such as Malassezia. However, because of its low neural sensitivity, it might be easy to worsen the skin
problems on the scalp. It is presumed that such severe skin circumstances make the scalp insensitive,
but increase the severity of the skin problems. Saint-Martory et al. reported that 36.2% of French
subjects say they suffer from sensitive scalp skin ; however, there are very few reports about
sensitive scalp skin [23,24]. Our study shows that, although the scalp has a low stratum corneum
function compared with to the forehead, the scalp skin has less sensitive sensory nerves. Therefore,
scalp skin might have easily induced skin problems and be more prone to worsening compared to other
regions of skin.
The scalp skin has less sensitive sensory nerves, despite its low stratum corneum function compared
to that of the forehead. Thus, the scalp skin can suffer from easily induced skin problems and more
adequate care should be necessary for maintaining healthy scalp skin.
This study was supported financially by the Kao Corporation. We thank our colleagues in the
Global R&D, Kao Corporation for their kind help during the study.
Cosmetics 2015, 2 392
Hiroko Takatoku, Takashi Kitahara, Hiroyuki Terazaki, Tadashi Nakamura and Koichi Ishida
conceived and designed the experiments; Hiroko Takatoku and Hiroyuki Terazaki performed the
experiments; Hiroko Takatoku and Yutaka Takagi analyzed the data; Yutaka Takagi wrote the paper.
Conflicts of Interest
No conflict of interest by disclosing any financial arrangements in this paper. All authors are
employees of Kao Corporation and this study was supported financially by Kao Corporation.
1. Hay, R.J. Malassezia, dandruff and seborrhoeic dermatitis: An overview. Br. J. Dermatol. 2011,
2. Turner, G.A.; Hoptroff, M.; Harding, C.R. Stratum corneum dysfunction in dandruff. Int. J.
Cosmet. Sci. 2012, 34, 298–306.
3. Gaitanis, G.; Magiatis, P.; Hantschke, M.; Bassukas, I.D.; Velegraki, A. The Malassezia genus in
skin and systemic diseases. Clin. Microbiol. Rev. 2012, 25, 106–141.
4. Warner, R.R.; Schwartz, J.R.; Boissy, Y.; Dawson, T.L., Jr. Dandruff has an altered stratum
corneum ultrastructure that is improved with zinc pyrithione shampoo. J. Am. Acad. Dermatol.
2001, 45, 897–903.
5. Bin Saif, G.A.; Ericson, M.E.; Yosipovitch, G. The itchy scalp—Scratching for an explanation.
J. Eur. Exp. Dermatol. 2011, 20, 959–968.
6. Ya-Xian, Z.; Suetake, T.; Tagami, H. Number of cell layers of the stratum corneum in normal
skin-relationship to the anatomical location on the body, age, sex and physical parameters.
Arch. Dermatol. Res. 1999, 291, 555–559.
7. O’goshi, K.; Iguchi, M.; Tagami, H. Functional analysis of the stratum corneum of scalp skin:
Studies in patients with alopecia areata and androgenetic alopecia. Arch. Dermatol. Res. 2000,
8. Myles, K.; Kalb, J.T.; Lowery, J.; Kattel, B.P. The effect of hair density on the coupling between
the tactor and the skin of the human head. Appl. Ergon. 2015, 48, 177–185.
9. Zhai, H.; Fautz, R.; Fuchs, A.; Bhandarkar, S.; Maibach, H.I. Human scalp irritation compared to
that of the arm and back. Contact Dermatitis 2004, 51, 196–200.
10. Essick, G.; Guest, S.; Martinez, E.; Chen, C.; McGlone, F. Site-dependent and subject-related
variations in perioral thermal sensitivity. Somatosens. Mot. Res. 2004, 21, 159–175.
11. Mehrabyan, A.; Guest, S.; Essick, G.; McGlone, F. Tactile and thermal detection thresholds of the
scalp skin. Somatosens. Mot. Res. 2011, 28, 31–47.
12. Rukwied, R.; Zeck, S.; Schmelz, M.; McGlone, F. Sensitivity of human scalp skin to pruritic stimuli
investigated by intradermal microdialysis in vivo. J. Am. Acad. Dermatol. 2002, 47, 245–250.
13. Masson, E.A.; Veves, A.; Fernando, D.; Boulton, A.J.M. Current perception thresholds: A new,
quick, and reproducible method for the assessment of peripheral neuropathy in diabetes mellitus.
Diabetologia 1989, 32, 724–728.
Cosmetics 2015, 2 393
14. Baquis, G.D.; Brown, W.F.; Capell, J.T.; Chaudhry, V.; Cros, D.; Drexinger, B.; Gelblum, J.B.;
Gilchrist, J.M.; Gitter, A.J.; Haig, A.J.; et al. Technology review: The Neurometer
Perception Threshold (CPT). Muscle Nerve 1999, 22, 523–531.
15. Kobayashi, H.; Kikuchi, K.; Tsubono, Y.; Tagami, H. Measurement of electrical current
perception threshold of sensory nerves for pruritus in atopic dermatitis patients and normal
individuals with various degrees of mild damage to the stratum corneum. Dermatology 2003, 206,
16. Lee, E.; An, S.; Lee, T.R.; Kim, H.K. Development of a novel method for quantitative evaluation
of sensory skin irritation inhibitors. Skin Res. Technol. 2009, 15, 464–469.
17. Parra, J.L.; Paye, M. EEMCO guidance for the in vivo assessment of skin surface pH.
Skin Pharmacol. Appl. Skin Physiol. 2003, 16, 188–202.
18. Tagami, H. Location-related differences in structure and function of the stratum corneum with
special emphasis on those of the facial skin. Int. J. Cosmet. Sci. 2008, 30, 413–434.
19. Mori, T.; Ishida, K.; Mukumoto, S.; Yamada, Y.; Imokawa, G.; Kabashima, K.; Kobayashi, M.;
Bito, T.; Nakamura, M.; Ogasawara, K.; et al. Comparison of skin barrier function and sensory
nerve electric current perception threshold between IgE-high extrinsic and IgE-normal intrinsic
types of atopic dermatitis. Br. J. Dermatol. 2010, 162, 83–90.
20. Tominaga, M.; Ozawa, S.; Tengara, S.; Ogawa, H.; Takamori, K. Intraepidermal nerve fibers
increase in dry skin of acetone-treated mice. J. Dermatol. Sci. 2007, 48, 103–111.
21. Florence, P.; Cornillon, C.; D’arras, M.F.; Flament, F.; Panhard, S.; Diridollou, S.; Loussouarn, G.
Functional and structural age-related changes in the scalp skin of Caucasian women. Skin Res.
Technol. 2013, 19, 384–393.
22. Saint-Martory, C.; Roguedas-Contios, A.M.; Sibaud, V.; Degouy, A.; Schmitt, A.M.; Misery, L.
Sensitive skin is not limited to the face. Br. J. Dermatol. 2008, 158, 130–133.
23. Misery, L.; Sibaud, V.; Ambronati, M.; Macy, G.; Boussetta, S.; Taieb, C. Sensitive scalp: Does
this condition exist? An epidemiological study. Contact Dermatitis 2008, 58, 234–238.
24. Misery, L.; Rahhali, N.; Ambonati, M.; Black, D.; Saint-Martory, C.; Schmitt, A.M.; Taieb, C.
Evaluation of sensitive scalp severity and symptomatology by using a new score. J. Eur. Acad.
Dermatol. Venereol. 2011, 25, 1295–1298.
© 2015 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license