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Shape Variability and Classification of Human Hair: A Worldwide Approach

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Abstract

Human hair has been commonly classified according to three conventional ethnic human subgroups, that is, African, Asian, and European. Such broad classification hardly accounts for the high complexity of human biological diversity, resulting from both multiple and past or recent mixed origins. The research reported here is intended to develop a more factual and scientific approach based on physical features of human hair. The aim of the study is dual: (1) to define hair types according to specific shape criteria through objective and simple measurements taken on hairs from 1442 subjects from 18 different countries and (2) to define such hair types without referring to human ethnicity. The driving principle is simple: Because hair can be found in many different human subgroups, defining a straight or a curly hair should provide a more objective approach than a debatable ethnicity-based classification. The proposed method is simple to use and requires the measurement of only three easily accessible descriptors of hair shape: curve diameter (CD), curl index (i), and number of waves (w). This method leads to a worldwide coherent classification of hair in eight well-defined categories. The new hair categories, as described, should be more appropriate and more reliable than conventional standards in cosmetic and forensic sciences. Furthermore, the classification can be useful for testing whether hair shape diversity follows the continuous geographic and historical pattern suggested for human genetic variation or presents major discontinuities between some large human subdivisions, as claimed by earlier classical anthropology.
... Nonetheless, similarities could still be explored between pig and human scalp hair. De la Mettrie et al. (2007) collected hair samples from 18 countries and classified eight main types of scalp hair based on curve diameter (CD), waves (w), and twists (i). In this study, all four different hair types were identified in pig referred to mouse. ...
... In comparison with the CD and w of human scalp hair (Figure 5A), the CDs of pig Awl, Auchene, and Zigzag hair types were greater than 20 and the CD of Guard_1 was 10.5-15. Besides, they were similar with Type I human scalp hair reported by De la Mettrie et al. (2007), while the CD of Guard_2 was 5.8-10.5 like Type II in human scalp hair ( Figure 5A). According to waves (w), human scalp hair was further divided into four other types (Figure 5C), while the w of all pig hair types was less than 3 µm (Figure 5B). ...
... (B) Number of waves (W) in five pig hair types. (C) Segmentation tree of eight human scalp hair; CD meter template derived fromBailey and Schliebe (1985); the graphics of the waves in (B) derived from De laMettrie et al. (2007). (D) Distribution of hair types in country groups. ...
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The pig is an increasingly popular biomedical model, but only a few in depth data exist on its studies in hair follicle (HF) morphogenesis and development. Hence, the objective of this study was to identify the suitability of the pig as an animal model for human hair research. We performed a classification of pig HF morphogenesis stages and hair types. All four different hair types sampled from 17 different body parts in pig were similar to those of human. The Guard_2 sub-type was more similar to type II human scalp hair while Guard_1, Awl, Auchene, and Zigzag were similar to type I scalp hair. Based on morphological observation and marker gene expression of HF at 11 different embryonic days and six postnatal days, we classified pig HF morphogenesis development from E41 to P45 into three main periods – induction (E37–E41), organogenesis (E41–E85), and cytodifferentiation (>E85). Furthermore, we demonstrated that human and pig share high similarities in HF morphogenesis occurrence time (early/mid gestational) and marker gene expression patterns. Our findings will facilitate the study of human follicle morphogenesis and research on complex hair diseases and offer researchers a suitable model for human hair research.
... The hair tresses, bought from the supplier International Hair Importers & Products, Inc (New York, NY, USA), were prepared from randomized and standardized fibers of brown natural human hair, with a curliness degree of type 3, according to de la Mettrie's scale [21], originally from people of Brazilian nationality. ...
... The literature indicates that the damage expressed by an increase in the number of soluble proteins extracted from the hair shaft in an aqueous medium is produced both by bleaching reagents and UV radiation [3,4,15,[21][22][23]30,31]. The partial overlapping of the uncertainty bands indicates that the results may be statistically compatible. ...
... For NA, the loss of mechanical resistance is noticeable after 60 h of exposure, while for DY, it is noticeable after 120 h of exposure. Although the effect of dyeing has already significantly impacted the fibers before sun exposure (Figure 2), possibly due to its damage being mainly associated with the deterioration of surface layers [1,27], some relevant mechanical properties were preserved before being irradiated, making it possible for the hair fibers to be more sensitive to the effects of radiation than the bleached fibers, which, in turn, undergo similar effects to those produced by UV radiation [3,4,15,[21][22][23]. ...
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Solar radiation is a significant source of damage to hair fibers. However, the instrumental measurement of the consequences of its interaction with hair fibers’ constituents remains a challenge. In this work, the flexabrasion methodology was investigated as a potential tool to quantify the damage to mechanical hair properties caused by solar rays. The in vitro experiment developed for this study simulated four initial conditions of human hair samples, which subsequently underwent different periods of exposure to the radiation emitted by a Xenon arc lamp source. The statistical analysis of the results characterized the methodology’s ability to evaluate the impact of solar radiation on the hair’s mechanical resistance. More evident effects were observed on natural fibers subjected to exposures of up to 60 h and over, corresponding to about 1.5 h per day of sun exposure in Rio de Janeiro over five months. The results point to flexabrasion as an option to evaluate the photoprotection efficacy offered by hair-care products.
... Brazil is a country with a very high ethnic mix [3] and, as a result, there is a great diversity of hair types. Hair can be classified into three major geo-racial groups: Afro, Asian, and Caucasian as shown in Figure 1a or can be further classified into up to 8 types according to the curvature of the hair, using the Segmentation Tree Analysis Method (STAM), shown in Figure 1b [4,5]. Figure 1: a) human hair shape from different geo-racial origins (Adapted from ROBBINS, 2012) and b) illustration of the appearance of eight types of curly hair [5]. ...
... Hair can be classified into three major geo-racial groups: Afro, Asian, and Caucasian as shown in Figure 1a or can be further classified into up to 8 types according to the curvature of the hair, using the Segmentation Tree Analysis Method (STAM), shown in Figure 1b [4,5]. Figure 1: a) human hair shape from different geo-racial origins (Adapted from ROBBINS, 2012) and b) illustration of the appearance of eight types of curly hair [5]. ...
... Some types of Asian or Caucasian straight hair, which have more circular cross-sectional shapes, are at the other limit of the texture spectrum. Hair from various ethnicities or racial origins have unique physicochemical properties (1)(2)(3)(4)(5). For example, African hair has a lower radial swelling rate than Asian and Caucasian hair. ...
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Synopsis In this study, we investigated differences in the various properties of textured hair as compared to straight hair. As representative hair types from both ends of the spectrum, we investigated the morphological and ultra ne structural characteristics of African and Caucasian hair. We took a profound look at African hair using eld emission scanning electron microscopy (FESEM), examining the exterior of the ber as well as its interior structure by analyzing thin cross-sections of hair. We found that it has unique morphology in both the exterior and interior of the ber. Some key features include the ber morphology at a point of curvature, concavity in the major axis, large distribution of melanin granules, and brillar structures (keratins) heavily coated with biological material (presumably lipids). We further examined the lipid characteristics of African and Caucasian hair using Fourier transform infrared imaging to map the lipid distribution within the cross-section of hair. Using dynamic vapor sorption, we observed the effect of lipid distribution in African hair and its in uence on water management properties. Finally, tensile strength data (break stress, percentage extension at break, etc.) agreed with data previously published in the literature. Expanding on this theme, we monitored the fracture patterns of bers extended to break using FESEM. Overall, African hair was found to exhibit various types of fracture patterns, especially at the point of curvature of the ber. The structures of the broken brillar proteins (intermediate laments) were signi cantly longer in Caucasian hair than in African hair.
... A number of genes, such as EDAR, FGFR2 and TCHH have been associated with hair curliness in different populations (e.g., [29][30][31]). Although recent studies classify human hair in eight types [32,33] distinguished by several parameters of the curliness of the hair, the traditional separation of hair curliness in the following four types remains: 'straight', 'wavy', 'curly', and 'kinky'. ...
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Chapter
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