Amounts of fibrous proteins and matrix substances in hairs of different races

How different is human hair? A critical appraisal of the reported differences in global hair fibre characteristics and properties towards defining a more relevant framework for hair type classification

This review critically appraises the reported differences in human hair fibre within three related domains of research: hair classification approaches, fibre characteristics and properties. The most common hair classification approach is based on geo-racial origin, defining three main groups: African, Asian and Caucasian hair. This classification does not account sufficiently for the worldwide hair diversity and intergroups variability in curl, shape, size and colour. A global classification into eight curl types has been proposed but may be too complex for reproducibility. Beyond that, hair cross-sectional shape and area have been found to have an inverse relation to curl: straighter fibres are circular with larger cross-sectional area, whilst the curlier fibres are elliptical with smaller cross-sectional area. These geometrical differences have been associated with bilateral vs homogenous distribution of cortical cell in curly vs straight hair respectively. However, there is no sufficient data demonstrating significant differences in hair amino composition, but proteomic studies are reporting associations of some proteins with curly hair. Eumelanin's relative abundance has been reported in all hair colours except for red hair which has a high pheomelanin content. Higher tensile and fatigue strength of straight hair are reported, however, curly hair fragility is attributed to knotting, and crack and flow formations rather than the structural variations. African hair has been found to have the highest level of lipids, whilst the water sorption of Caucasian hair is the highest, and that of Asian hair the lowest. Not all comparative studies clearly report their hair sampling approaches. Therefore, to strengthen the robustness of comparative studies and to facilitate cross-study data comparisons, it is recommended that the following hair defining characteristics are reported in studies: hair cross sectional diameter/area, curl type, hair assembly colour, as well as where possible donor data (age/gender) and sample pooling approach.

On Hair Care Physicochemistry: From Structure and Degradation to Novel Biobased Conditioning Agents

Hair is constantly exposed to various adverse external stimuli, such as mechanical or thermal factors, that may cause damage or cause it to lose its shine and smooth appearance. These undesirable effects can be minimized by using hair conditioners, which repair the hair and restore the smooth effect desired by the consumer. Some of the currently used conditioning agents present low biodegradability and high toxicity to aquatic organisms. Consumers are also becoming more aware of environmental issues and shifting their preferences toward natural-based products. Therefore, developing novel, sustainable, natural-based derivatives that can act as conditioning agents in hair care products and thus compete with the traditional systems obtained from non-renewable sources is highly appealing. This paper presents the key physicochemical aspects of the hair conditioning process, including hair structure and degradation, and reviews some of the new alternative conditioning agents obtained from natural resources.

Ethnic hair: Thermoanalytical and spectroscopic differences

BACKGROUND

The aim of this study is to characterize and detect the possible differences among the hair of three different ethnicities: African, Asiatic and Caucasian.

MATERIALS AND METHODS

The differences in water adsorption/desorption behaviour of hairs were studied using a thermogravimetric balance and compared with the analysis of the lipid distribution and order using synchrotron-based Fourier transform infrared microspectroscopy. Besides, the thermal thermogravimetry (TG) and differential scanning calorimetry (DSC) analyses on human hair were executed.

RESULTS

Differences in the diffusion coefficients were evidenced. African hair exhibited increased permeability. Caucasian hair displayed a higher water absorption capability with increasing humidity but with a slow diffusion rate. The Asian fibre appeared to be more resistant to hydration changes. The spectroscopic analysis showed notable differences in the cuticle lipids. The African cuticle exhibited more lipids with a lower order bilayer. The outmost layer of Caucasian fibres contained more ordered lipids, and the Asian fibres show a very low level of lipids on the cuticle region. The DSC results indicate no difference in the thermal stability and TG showed higher water content in the Caucasian fibre and a possible lower cysteine disulphide bond content in the African hair matrix.

CONCLUSION

The triple approach demonstrated the permeability differences among the ethnic fibres and their correlation with the properties of their cuticle lipids. These differences could have particular relevance to the hair care cosmetic market.

In vitro determination of Mexican Mestizo hair shaft diameter using optical coherence tomography

BACKGROUND

Mexican mestizo population has a pluriethnic mixture of Amerindian, European and African ancestry, predominant in most Latin American countries. Until now, there are no reports about hair characteristics in this population, necessary to define normal values, for hair diseases evaluation and comparison among other ethnic groups.

METHODS

The VivoSight^® swept-source multibeam optical coherence tomography system was used to evaluate hair diameter and shape in 30 females. Three hair samples from each volunteer were measured transversely along three distances, generating nine cross-sectional images, two measurements per image and 18 measurements per patient for a total of 540 diameter measurements.

RESULTS

Minimum hair diameter (n = 540) was 0.06 mm while maximum was 0.14 mm. Mean diameter was 0.10 ± 0.01 mm as compared with Asian hair, which ranges from 0.08 mm to 0.12 mm. On morphological analysis, Mexican Mestizo hair tends to have a round shape with homogenous diameters, resembling Caucasian and Asian hair.

CONCLUSION

Mexican hair is similar to Asian hair in diameter and shape and can be classified as 'thick' hair, which make it more resistant and with more volume. Cosmetic products intended to improve hair care in this population must to consider this characteristic.

Hair care practices and structural evaluation of scalp and hair shaft parameters in African American and Caucasian women

How African American hair fragility relates to hair care practices and biologic differences between races is not well understood. To assess the differences between perceptions of hair health, hair care practices, and several biologic hair parameters between Caucasian and African American women. A questionnaire on perceptions of hair health and hair care practices was administered. Biological and structural parameters of hair shaft and scalp, including growth, density, diameter, cycle, breakage, and scalp blood flow were also assessed in this case-control study. Significant differences between the Caucasian and African American women were observed in the questionnaire and biologic study data. Regarding self-reported perceptions of hair health, there were differences in the following: hair shaft type (P < 0.001), hair breakage (P = 0.040), and desire to change hair (P = 0.001). Regarding self-reported hair care practices, there were differences in the following: location of haircutting (P = 0.002) and washing (P = 0.010), washing frequency (P < 0.001), chemical relaxer use (P < 0.001), hooded hair dryer use (P < 0.001), and hair shaft conditioner use (P = 0.005). The two groups had similar practices in regard to the use of hair color, frequency of hair color use, chemical curling agents, and handheld blow dryer use. Regarding biological and structural parameters, there were differences in the following: hair growth rate (P < 0.001), density (P = 0.0016), diameter (P = 0.01), number of broken hairs (P < 0.001), and blood flow (P = 0.03). There was no significant difference in hair cycle parameters.The differences in hair care practices and hair fiber morphology among African American women may contribute to clinically observed variation in hair fragility and growth.

Traction alopecia: how to translate study data for public education--closing the KAP gap?

Traction alopecia (TA) affects up to 32% of women and 22% of high school girls with Afro-textured hair but can start in the preschool years. Traction induces inflammation and follicle damage. The risk of TA increases with symptomatic traction and combined hairstyles. To influence the practice of hairdressers and at risk individuals and help narrow the knowledge, attitudes, and practices (KAP) gap, scientific data should be translated into simple messages like "tolerate pain from a hairstyle and risk hair loss" and "no braids or weaves on relaxed hair". With appropriate education and public awareness, TA could potentially be eradicated.

'Relaxers' damage hair: evidence from amino acid analysis

BACKGROUND

'Relaxers' are used by more than two thirds of African females to straighten hair, with easy grooming and increased length often cited as reasons. A recent study reported relaxed hair lengths much shorter than expected, suggesting increased fragility; the potential for scalp inflammation and scarring alopecia remains unclear.

OBJECTIVE

To investigate the biochemical effects of 'relaxers' on hair.

METHODS

With informed consent, included participants represented 3 groups: natural hair, asymptomatic relaxed hair, and symptomatic (brittle) relaxed hair. Biochemical analysis was performed by using a Biochrom 30 amino acid analyzer. Differences in amino acid levels were assessed using either Wilcoxon rank sum test or matched-pairs signed-rank test.

RESULTS

There was a decrease in cystine, citrulline, and arginine; however, an increase in glutamine was found in all relaxed compared to natural hair. Cystine levels (milligram per gram amino acid nitrogen) were similar in natural proximal and distal hair: 14 mg/g (range, 4-15 mg/g) versus 14 mg/g (range, 12-15 mg/g); P = .139. In asymptomatic relaxed hair, cystine levels were higher in less frequently relaxed samples proximal to scalp: 7.5 mg/g (5.6-12) versus 3.3 mg/g (1.3-9.2); P = .005. Cystine levels in distal asymptomatic relaxed and symptomatic relaxed hair were similar to each other and to those in the genetic hair fragility disease trichothiodystrophy.

LIMITATIONS

It was not possible to analyze lye and no-lye 'relaxers' separately.

CONCLUSIONS

'Relaxers' are associated with reduced cystine consistent with fragile damaged hair. A decrease in citrulline and glutamine has been associated with inflammation; prospective studies are needed to investigate whether or how 'relaxers' induce inflammation.

African hair length: The picture is clearer

Three subjects with virgin African hair combed daily had surprisingly short hair length measurements of 40.1 +/- 14 mm, 60 +/- 10 mm, and 69 +/- 20 mm at 6 months, 1 year, and 3 years after a haircut, respectively. This observation raises the possibility that combing African hair on a daily basis may result in the equivalent of a daily haircut in some people. This observation is based on few participants and will require confirmation in population studies.

Apparent fragility of African hair is unrelated to the cystine-rich protein distribution: a cytochemical electron microscopic study

A feature of black African hair is an apparent increased fragility of the hair shaft compared to other ethnic groups (as measured by the tensile force needed to break the hair fibre). This has certain similarities to that reported for trichorrhexis nodosa (weathering secondary to physical damage) and trichothiodystrophy [a genetic disorder associated with reduced cystine (sulphur)-rich proteins and increased fragility]. In the present study, the distribution of the cystine-rich proteins in the hair of black Africans was compared to that of Caucasian and Asian volunteers, plus patients with trichorrhexis nodosa and trichothiodystrophy, using transmission electron microscopy and specific silver stains. It was found that the silver staining pattern of the hair shafts of black Africans was similar to that observed for Caucasians, Asians and also patients with trichorrhexis nodosa. The cuticular cells exhibited an electron dense A layer and exocuticle, and in the cortex the microfibrils forming the macrofibres were outlined by electron-dense material. This contrasts with the abnormal distribution of the cystine-rich proteins seen in trichothiodystrophy. This study is the first formal comparison of the cystine-rich proteins in the various racial groups and shows that there is no abnormality in their distribution in black African hair shafts compared to the other ethnic groups. Therefore, the excessive structural damage observed in the African hair shafts is consistent with physical trauma (resulting from grooming) rather than an inherent weakness due to any structural abnormality.

Human hair shape is programmed from the bulb

BACKGROUND

Few biological data on curly hair follicles have been reported in the literature.

OBJECTIVES

To investigate the growth and morphology of curly hair follicles.

METHODS

Follicles were dissected from scalp skin samples from African, Guyanese and caucasian volunteers and were observed macroscopically, in culture in William's E medium, and by immunohistochemistry.

RESULTS

Macroscopic study of scalp biopsies obtained from African volunteers showed that the dermal implantation of follicles was curved with a retrocurvature at the level of the bulb, as opposed to a straight shape in caucasian follicles. The bulb itself was bent, in the shape of a golf club, while both the outer root sheath (ORS) and the connective tissue sheath were dissymmetrical along the follicle. In vitro growth of curly hair follicles was slightly slower than that of caucasian follicles but, more importantly, the curvature was maintained in the hair shaft produced in vitro. As shown by immunohistochemistry, the proliferative matrix compartment of curly hair follicles was asymmetrical, Ki-67-labelled cells being more numerous on the convex side and extending above the Auber line. On the convex part of the follicle, the ORS was thinner and the differentiation programmes of the inner root sheath and hair shaft were delayed. Furthermore, some ORS cells expressed alpha-smooth muscle actin protein on the concave side of the curvature, reflecting a mechanical stress.

CONCLUSIONS

Hair curliness is programmed from the bulb and is linked to asymmetry in differentiation programmes.

Hair shape of curly hair

The hair follicle is a unique composite organ, composed of epithelial and dermal compartments interacting with each other in a surprisingly autonomous way. This is a self-renewing organ that seems to be a true paradigm of epithelial and mesenchymal interactions. Each of the follicular compartments is endowed with a specific differentiation pathway under the control of an intricate network of growth factors, cytokines, and hormones. As observed for ethnic hairs, even the shape of the hair shaft is intrinsically programmed from the bulb.

Current research on ethnic hair

This study collected qualitative and quantitative data about the morphology, structure, geometry, water swelling, and mechanical properties of hair fibers from subjects of different ethnic origins. X-ray analysis, cross-sectional measurements, tensile testing, and water swelling were performed on samples of hair collected from Caucasian, Asian, and African subjects. No differences in the intimate structures of fibers were observed among these 3 types of hairs, whereas geometry, mechanical properties, and water swelling differed according to ethnic origin. In addition, the behavior of hair fiber under mechanical stress was visualized with environmental scanning electron microscopy.

What is normal black African hair? A light and scanning electron-microscopic study

BACKGROUND

The hair of normal black Africans forms a mat of tightly interwoven hair shafts. The effect of this on the structure of the hair shaft and the response to grooming is unknown.

OBJECTIVE

Our purpose was to use light and scanning electron microscopy (SEM) to examine the structure of Negroid-type hairs and effects of combing in black African volunteers.

METHODS

Hair samples were collected, by combing, from Africans and compared with those from Caucasian and Asian volunteers. The volunteers had never used chemical treatments. Their hair had not been cut for at least 1 year and grooming had been limited to shampooing, drying, and combing.

RESULTS

More than 2000 hairs in 12 African volunteers were examined by light microscopy. The hairs appear as a tight coiled springlike structure. Many shafts exhibited knots (10%-16% vs 0.15%) and appear broken compared with hair shafts from other ethnic groups. SEM of African hairs showed features consistent with repeated breaks of the shaft. Examination of hairs in situ showed interlocking of hair shafts.

CONCLUSION

These observations provide an understanding of the physical nature of, and effect of combing on, black African hair.

The incorporation of dyes into hair as a model for drug binding

The binding of charged substances from external aqueous media to hair has been investigated through the use of fluorescence microscopy. Eleven hair samples, reflecting various ethnic groups and cosmetic treatments, were tested. Rhodamine 6G, a cationic dye representative of drugs such as cocaine and opiates, showed incorporation throughout the hair of all samples except one. In contrast, fluorescein, an anionic dye representative of drugs such as THC carboxylic acid, was not readily incorporated. The incorporation of rhodamine 6G was faster for chemically 'straightened' and bleached African-American female hair than for untreated hair. Incorporation of rhodamine 6G followed a pH dependence, but an ionic strength dependence could not be established. These studies support three postulates: (1) electrostatic interactions explain the preferential binding of cationic drugs of abuse to hair; (2) the hair matrix, or the non-helical portion of hair, is accessible to external solutions and thus subject to contamination; and (3) cosmetic treatments may alter the helical portion of hair thereby increasing its accessibility to external contamination.

Cocaine in the hair of mother-infant pairs: quantitative analysis and correlations with urine measures and self-report

A sample of mothers who had used crack cocaine while pregnant was evaluated during the postpartum period before random assignment to drug treatment. Mean infant age was 74 days. Paired hair samples were acquired from 63 mothers and 63 infants. Maternal urine was screened for cocaine and benzoylecgonine; three different drug use self-report measures were also collected. Normalizing transformations of all hair and urine data preceded analyses. The initial correlation of mother and infant hair (r = .41, N = 62, P = .001) was strengthened (r = .62, N = 30, P < .0005) by removing from the dataset maternal hair independently judged to be damaged. Damage to hair is associated with certain types of "hair care" products. The damaged maternal hair bore no quantitative relationship to infant hair (r = -.04, N = 30, P = .41). Poor quality hair samples could have been partly anticipated because self-reported use of hair products had a significant contingent relationship to laboratory-judged damage to hair (Z kappa = 2.28, P = .01). Maternal urine benzoylecgonine correlated with maternal hair (r = .41, N = 60, P = .001) and, of course, with maternal urine cocaine (r = .63, N = 60, P < .0005). None of the three self-report measures (use in past 30 days, duration since first use, average regular use) significantly correlated with any of the hair or urine measures. Factor analysis of drug use variables identified three factors possibly representing long-term use, recent use, and some artifact of self-report. In summary, hair analysis may provide a quantitative index of exposure when the hair is not damaged. The amount of self-reported drug use could not be corroborated with analytic measures of hair or urine. Studies in which self-reported cocaine use is a scalar variable should be interpreted cautiously.