日本香粧品学会誌

Vol. 37, No. 3, pp. 165–Effect170（2013）
of Heat Treatment on Human Hair Keratin Film

165

〈Regular Article〉

Effect of Heat Treatment on Human Hair Keratin Film
Toshihiro FUJII ＊, 1, Yuka TAKASHIMA1, Shunsuke TAKAYAMA1,Tomoyuki KAWASOE2
Yumiko ITO1，(Accepted: April 23, 2013)

Abstract
Human hair keratin ﬁlm consisting of ﬁne ﬁbrous and particle structures has been utilized as an alternative device tohair samples. Since application of heat is a well-known factor causing hair damage, the thermal effects on the keratin ﬁlms
and hair samples were examined focusing on color change, morphological observation, protein solubility, and oxidative
proteins. The opaque white appearance of the keratin ﬁlm changed to a yellow/light brown color by the thermal treatments
at more than 170℃. This color change at 170℃ and higher was also detected by spectrophotometry. Scanning electron
microscopy (SEM) observation showed that there was little change in the ﬁne structures of the keratin ﬁlms and hairsamples even after a thermal treatment at 200℃ for 10 min. When protein solubility of heat-treated keratin ﬁlms and hairsamples were examined using a solution containing dithiothreitol (DTT) and urea, the amounts of proteins solubilized fromheat-treated keratin ﬁlms and hair samples were less than those from untreated keratin ﬁlm and hair samples. The protein solubility decreased in a heating time- and temperature-dependent manner. A linear relationship between solubilized proteins
and a heating temperature of 110 to 160℃ was found. Compared to hair samples, the degree of change was clearly evident in
the keratin ﬁlms. The solubilized proteins consisted of keratin and keratin-associated proteins (KAPs). The amount ofcarbonylated proteins increased in the ﬁlms treated at 120–180℃. This data suggests that thermal treatment promotes
protein oxidization and induce the formation of Stable Structure which has not yet been identiﬁed. In any event, hairthermal damage will be quantitatively evaluated using the keratin ﬁlms in place of hair samples.
Key words:

1.

human hair keratin ﬁlm, heat stability, thermal sensitivity, protein solubility, comparison with hair sample.

consisting of keratin ﬁbers.
In the hair research involving development of hair carerelated products, heterogeneous characteristics of hairsamples due to individually different diameters, histories, andvariations between tips and roots seem to be present in theaccurate analyzer as noise. In order to obtain the accurate datafrom hair samples, numerous experiments are required. Thus,an alternative to hair samples, which can be the embodimentof average hair has been sought. Since hair mainly consists ofﬁlamentous proteins, we have solubilized them in the solution
and succeeded in developing a ﬁlm by inducing the selfassembly of proteins11). This two-dimensional keratin ﬁlm
reacts in the same manner as three-dimensional hair samples:the formation of oxidative proteins when irradiated withUV12), 13), the formation of cysteic acid by bleach (oxidative)
treatment14), and elution of low molecular weight proteinswhen treated with perm (reductive) solutions15), 16). In eachcase, compared to hair samples, the ﬁlms showed higher
sensitivity in detection. The formation of cysteic acid wasinvestigated using FT-IR (Fourier transform infraredspectroscopy) and the spectra were very similar in both theﬁlm and hair samples. When treating hair and ﬁlm bycommercial bleaching agent, the peak of cysteic acid (around−11,041 cm ) was detected14). The peak height of the keratin

Introduction

Human hair is frequently subjected to thermal treatment
when it is dried after washing, or when it goes through a process of hair styling. The use of hair irons at high temperaturesin addition to hair dryers also causes hair damage. Thus, theeffect of thermal treatments on hair has been a subject ofresearch. The cuticles which make up the surfaces of hair are
known to have lift-ups and to form blisters that are porous
ﬂares in hair caused by the heat treatment1)–3). Therefore,
the coefﬁcient of friction in damaged hair by such factors
increases4). The technology to visualize ﬂips and fuzz indamaged cuticles quantitatively has also been developed4)–6).
The formation of hollow spaces within end-cuticles wasobserved by transmission electron microscopy (TEM), whichsuggested the decrease of interaction between cuticles andcortex. Mechanical strength of hair mainly depends on thecortex, and it is known that when hair is treated by heat under
wet conditions, its mechanical strength decreases4). Thechanges within hair have been reported as follows: change inenthalpy and dynamic of water7), decomposition of tryptophan
in the composing proteins8), 9), and cross-linkage among proteins10). Therefore, it is considered that thermal changes in hair
happen not only at the cuticle but also at the cortex
1, ＊Faculty of Textile Science and Technology, Shinshu University(3–15–1 Tokida, Ueda, Nagano 386–8567, Japan)
連絡先 E-mail: fujiit1@shinshu-u.ac.jp

2SHISEIDO Co., Ltd., Research Center (2–2–1 Hayabuchi, Tsuzuki-ku,
Yokohamashi, Kanagawa 224–8558, Japan)