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Hair is important to our appearance as well as to protect our heads. Human hair mainly consists of proteins (80-85%), melanin pigments (0-5%), water (10-13%), and lipids (1-6%). The physicochemical properties of hair have been studied for over 100 years. However, they are not yet thoroughly understood. In this review, recent progress and the latest findings are summarized from the following three perspectives: structural characteristics, delivery and distribution of active ingredients, and hair as a template. The structural characteristics of hair have been mainly investigated by microscopic and/or spectroscopic techniques such as atomic force microscopy integrated with infrared spectroscopy (AFM-IR) and rheological measurements. The distribution of active ingredients has been generally evaluated through techniques such as nanoscale secondary ion mass spectrometry (NanoSIMS). And finally, attempts to explore the potential of hair to be used as a substrate for flexible device fabrication will be introduced.

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The aim of the study is a comparative analysis to investigate human hair metal profiles of adolescents residing near petrochemical plants (Sicily, Italy). We selected the small town of Augusta, Gela, and Pace del Mela, and a control area made up of the towns characterized by low anthropogenic activity. Twenty trace elements were measured in samples of scalp hair from adolescents (11-14 years old) of both genders. Hair samples were cleaned using a rigorous cleaning method, mineralized, and processed for analyses by inductively coupled plasma-mass spectrometry (ICP-MS). In industrial sites, zinc was always the most abundant element, ranging from186 to 217 µg g-1. Following zinc, the elements Al, Ba, Cu, Fe, and Sr were in the range 1-20 µg g-1. The remaining elements had concentrations < 1 µg g-1. The comparison with adolescents living in suburban area highlighted that As, Ba, Mn, Sr, U, and V have the highest median concentrations in an industrial location. An industrial factor (As, Mn, Sr, U, and V) and an urban factor (Cd, Cr, Cu, Mo, Ni, and Sb) were distinguished by the multivariate statistical analysis between a cohort residing in urban and industrial areas. Statistically significant differences (Kruskal-Wallis test, p < 0.05) between the genders were found for Ba, Mn, Ni, Sr, and V in all industrial sites with median concentrations higher in females' hair than males'. The data confirm that the study areas are heavily affected by industrial and urban emissions of metals and metalloids, representing a potential hazard to the local population.

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Multi-isotope analysis (e.g., Sr-Pb-O-H-C-N) of human scalp hair is routinely used in forensic investigations of human remains to constrain the geographic origin of unidentified bodies, and to investigate antemortem mobility patterns. However, while it is known that postmortem processes can affect the preservation of, or even overprint, the biogenic isotopic signatures in hair, the speed and nature of these processes have rarely been studied. This study investigates the effects of decomposition and environment on the H-Pb-Sr isotope compositions of human hair as well as the relationship between structural hair shaft degradation and isotopic signature change over time. Human scalp hair samples from four body donations were collected at different stages throughout gross body decomposition. The willed-donated bodies were placed to decompose outdoors at the Forensic Anthropology Research Facility (FARF) at Texas State University. Hair fibres from two of the donations were examined using scanning electron microscopy (SEM) and high-resolution light microscopy (HRLM). Chemical and microbiological degradation of hair fibres occurred rapidly after placement of the body outdoors. Measurements of scalp hair isotopic composition demonstrated that H-Pb-Sr isotope ratios were altered within days after environmental exposure, presumably by deposition, leaching and/or exchange with the local bioavailable soil, and vapour. The degree of physical hair degradation and changes in H-Pb-Sr isotope composition were not correlated. We conclude that antemortem isotopic H-Pb-Sr isotope ratios are difficult to recover in hairs derived from decomposing whole bodies.

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In this study, we investigated and compared characteristics of the bacterial community structures on hair (scalp hair) and scalp in 18 individuals. Significant differences were found between the sites, in terms of cell density, alpha and beta diversity, and relative abundance of the phyla, Firmicutes and Proteobacteria, whereas no difference was found in relative abundance of the phylum Actinobacteria. Bacteria of the genus Cutibacterium showed similar relative abundance at both sites, whereas those of genus Pseudomonas were highly abundant on hair, and those of genus Staphylococcus were significantly lesser in abundance on hair than on scalp. Statistical correlations between the sites were high for the individual relative abundance of five major operational taxonomic units (OTUs). This suggests that the bacterial community structure on hair is composed of hair-specific genus, Pseudomonas, and skin-derived genera, Cutibacterium and Staphylococcus, and is distinguishable from other human skin microbiomes.

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The main aim of this study was to assess the level of mercury accumulation in the hair of students studying in the Vologda Region, Russia. Particular attention is devoted to clarifying the relationship between the metal concentration in the hair and the amount of fish in the diet. It was found that the mercury content in the hair of Vologda Region residents aged 17-21 is in the range from less than 0.002 mg/kg to 1.69 mg/kg, the median of the indicator for the entire sample is 0.14 mg/kg. The median value of mercury content in the hair of males (0.12 mg/kg) is lower than in the hair of females (0.16 mg/kg). The lowest metal concentrations were observed in individuals living in the city of Cherepovets and the highest metal concentration among the entire sample and in females in the western areas, and males in the eastern areas of the Vologda Region. The concentration of metal in the hair of the urban population is lower than in subjects living in rural areas. A higher metal content in the hair was recorded in individuals whose diet usually contains fish twice a month.

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Multi-isotope analysis (e.g., Sr-Pb-O-H-C-N) of human scalp hair is routinely used in forensic investigations of human remains to constrain the geographic origin of unidentified bodies, and to investigate antemortem mobility patterns. However, while it is known that postmortem processes can affect the preservation of, or even overprint, the biogenic isotopic signatures in hair, the speed and nature of these processes have rarely been studied. This study investigates the effects of decomposition and environment on the H-Pb-Sr isotope compositions of human hair as well as the relationship between structural hair shaft degradation and isotopic signature change over time. Human scalp hair samples from four body donations were collected at different stages throughout gross body decomposition. The willed-donated bodies were placed to decompose outdoors at the Forensic Anthropology Research Facility (FARF) at Texas State University. Hair fibers from two of the donations were examined using scanning electron microscopy (SEM) and high-resolution light microscopy (HRLM). Chemical and microbiological degradation of hair fibers occurred rapidly after placement of the body outdoors. Measurements of scalp hair isotopic composition demonstrated that H-Pb-Sr isotope ratios were altered within days after environmental exposure, presumably by deposition, leaching and/or exchange with the local bioavailable soil, and vapor. The degree of physical hair degradation and changes in H-Pb-Sr isotope composition were not correlated. We conclude that antemortem isotopic H-Pb-Sr isotope ratios are difficult to recover in hairs derived from decomposing whole bodies.

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An attempt to understand and explain a peculiarity that was observed for curly fibres during experimentation revealed disparate literature reporting on several key issues. The phenotypical nature of curly fibres is only accurately understood within the larger scope of hair fibres, which are highly complex biological structures. A brief literature search produced thousands of research items. Besides the large amount of information on the topic, there was also great variability in research focus. From our review, it appeared that the complexity of hair biology, combined with the variety of research subtopics, often results in uncertainty when relating different aspects of investigation. During the literature investigation, we systematically categorized elements of curly hair research into three basic topics: essentially asking why fibres curl, what the curly fibre looks like and how the curly fibre behaves. These categories were subsequently formalized into a curvature fibre model that is composed of successive but distinctive tiers comprising the elements in curly hair research. The purpose of this paper is twofold: namely to present (i) a literature review that explores the different aspects of curly human scalp hair and (ii) the curvature fibre model as a systemized approach to investigating curly hair.

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In order to explore the level of heavy metal pollution in human hair of residents in Huainan City and provide theoretical guidance for prevention and control of heavy metal pollution, human hair samples from 174 residents in Huainan City were collected so that heavy metal (Cr, Cu, Pb, Zn, As, and Fe) concentrations in scalp hair could be tested, and meanwhile their relationship with sex, age, and spatial distribution characteristics could be explored as well. According to the final analysis, the average concentration of Cr, Pb, Cu, Fe, Zn, and As in human hair amounted to 1.56, 6.41, 14.96, 31.13, 166.54, and 1.07 mg/kg. The highest average of Cr and Pb contents in human hair occurred in the area of Xiejiaji District; Fe, Zn, and Hg were in Datong District; and Cu and As were in Panji District respectively. Overall, the lowest risk of heavy metal exposure existed in Tianjia'an District. Heavy metal content in hair varied across sexes and ages. Pb concentration in hair would decrease as age increased. The highest Pb concentration appeared in children between ages 0 and 10, the amount of which was significantly different from that in other age groups; hence, children appear to be more susceptible to Pb pollution than other ages. Contents of Cr, Fe, Zn, and As in hair would also increase with age; Fe content in hair was particularly correlated with age. The contents of Cr, Pb, Fe, and As in men's hair were higher than those in women's, whereas the case of Cu and Zn was just the opposite. There were significant differences between sexes concerning the contents of Cr, Cu, and As, and a highly significant difference about Zn between sexes as well. These results indicated that the contents of heavy metal in residents' hair would be closely related to the features of the local environment and population.

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Bacterial communities on various parts of the human body are distinct. We were the first to report the existence of a stable bacterial community on human scalp hair and demonstrated that an analysis of its structure by terminal restriction fragment length polymorphism (T-RFLP) is helpful for individual discrimination. However, the ecology of the bacterial community on human scalp hair has not yet been elucidated in detail. We herein investigated the mode, quantity, and phylogeny of bacterial communities on the human hair shaft and root and showed the results obtained from one representative individual. Direct SEM observations of hair, without a pretreatment, confirmed the ubiquitous presence of bacteria-like coccoids and rods on the shaft and root of hair from the human scalp, with 105-106 cells cm-2 of hair and 107 cells cm-2 of hair, respectively. These values corresponded to the 16S rRNA gene copy numbers obtained by qPCR. These numbers were not significantly affected by detergent washing. These results represented those obtained from many individuals with different hair lengths, ages, and gender. The major OTUs on the human scalp hair shaft and root were the same and included two species of Pseudomonas (phylum Proteobacteria), Cutibacterium and Lawsonella (phylum Actinobacteria), and Staphylococcus (phylum Firmicutes). These results suggest that major bacteria on the human hair shaft are indigenous and derived from the hair root.

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Multi-element stable isotope analyses of δ13C, δ15N, δ34S and δ2H values were performed along scalp hair strands to detect isotopic changes resulting from different stays abroad. One hair strand with a hair length of more than 50 cm originated from a German woman, who frequently made long-distance travels of 1 to 4 weeks. The second hair strand with a length of 15 cm was taken from a Japanese woman who went to Germany for a period of some months. Stable isotopic influences due to the stays abroad were clearly reflected in the 5-mm segments along the proximal part of the hair strand; whereas in the more distal parts, the isotopic influences were blurred. This can be regarded as the result of the highly variable intra-individual hair growth rate of single hairs of at least ± 30% compared to the mean growth rate. Consequently, the initial isotope signal obtained by short stays abroad became rapidly attenuated in the more distal parts of the hair strand. Furthermore, decreasing sulphur content associated with higher sulphur isotope values was observed with increasing hair length. The isotope shifts along the scalp hair strand, provoked by dietary changes at new locations, appeared at such points of hair length, which correspond well with the maximum growth rate of single hairs. Consequently, the exact date for any changes coming along with isotopic shifts may be calculated by best approach considering a hair growth value of 1.4 cm per 30 days, instead of the commonly used mean monthly hair growth rate of 1.1 cm. This may be important in forensics, if detailed information about a person's recent lifetime should be figured out by segmental scalp hair analyses.

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BACKGROUND AND SIGNIFICANCE: Still vast majority of the population in urban and rural set up using varied water quality for their day today washing of their hair in many parts of the countries may suffer or experience rough hair or uncombable syndrome. The quality of maintaining healthy hair may be impaired due to salty ions from water sources, dyes, or pollutants etc., We have identified a well-known instrumental technique SEM/SDD-EDS method to identify and estimate the waterborne minerals in the scalp hair cuticle in a non-destructive way. MATERIALS AND METHODS: Identify volunteers of urban and rural folks using treated or untreated water for their routine hair wash at least for two consecutive years and examine their scalp hair cuticle using SEM/SDD- EDS. RESULTS: Water borne minerals calcium and aluminium pick up were distinctly identified in the scalp hair cuticle as reflected by the quality of water used in urban and rural set up. Further restoration of lipid layer through prior application of coconut oil and or usage of conditioners prevents calcium pick up. Thereby, SEM/SDD-EDS is one of the suitable techniques to estimate the concentration of waterborne minerals in the scalp hair cuticle.

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The estimated daily intakes (EDIs) of six trace elements (Cu, Zn, Pb, Cd, Hg, and As) in vegetables (leafy vegetable, i.e., bok choy, fruit vegetables, i.e., cucumber and tomato, and other categories, i.e., mushroom, kidney bean, and potato), cereals (rice and wheat flour), and meats (pork, mutton, and beef) most commonly consumed by adult inhabitants of Qiqihar, Northeastern China, were determined to assess the health status of local people. The average EDIs of Cu, Zn, Pb, Cd, Hg, and As were with 20.77 µg (kg bw)-1 day-1 of Cu, 288 µg (kg bw)-1 day-1 of Zn, 2.01 µg (kg bw)-1 day-1 of Pb, 0.41 µg (kg bw)-1 day-1 of Cd, 0.01 µg (kg bw)-1 day-1 of Hg, and 0.52 µg (kg bw)-1 day-1 of As, respectively, which are below the daily allowance recommended by FAO/WHO. However, the maximum EDIs of Pb and Cd were 4.56 µg (kg bw)-1 day-1 and 1.68 µg (kg bw)-1 day-1, respectively, which are above the recommended levels [i.e., 3.58 µg (kg bw)-1 day-1 for Pb and 1.0 µg (kg bw)-1 day-1 for Cd] by FAO/WHO. This finding indicates that the potential health risk induced by daily ingestion of Pb and Cd for the local residents should receive a significant concern. Similarly, we detected elevated Pb and Cd concentrations, i.e., with average of 13.58 and 0.60 mg kg-1 dw, respectively, in the adult scalp hairs. Consumption of rice, potato, bok choy, and wheat flour contributed to 75 and 82% of Pb and Cd daily intake from foodstuffs. Nevertheless, human scalp hair is inappropriate biological material for determination of the nutritional status of trace elements in this region.

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Human scalp hair samples were collected and used to assess exposure to toxic elements and essential elements in the state of North Carolina, USA using accelerated microwave assisted acid digestion and inductively coupled plasma optical emission spectroscopy (ICP-OES). The figures-of-merit of the ICP-OES were appropriate for elemental analysis in scalp hair with detection limits as low as 0.0001 mg/L for Cd, good linearity (R2 > 0.9978), and percent recoveries that ranged from 96 to 106% for laboratory-fortified-blanks and 88-112% for sample spike recovery study. The concentrations of essential elements in scalp hair were larger than those of toxic elements, with Ca having the highest average concentration (3080 µg/g, s = 14,500, n = 194). Some of the maximum concentrations observed for As (65 µg/g), Ni (331 µg/g), Cd (2.96 µg/g), and Cr (84.6 µg/g) in individual samples were concerning, however. Samples were statistically analyzed to determine the influence of race, gender, smoking habits, or age on the elemental concentrations in scalp hair. Higher concentrations of essential elements were observed in the scalp hair of Caucasians, females, and non-smokers, and the differences were often significant at a 90% confidence level. Several pairs of essential elements, for example Ca-K, Ca-Mg, and Ca-Zn, were strongly correlated in Caucasian hair but uncorrelated in African-American hair. Similarly, essential elements were strongly correlated in female hair but weakly correlated in male hair. Toxic element pairs (As-Cd, As-Se, Pb-As, and Se-Cd) were strongly correlated in the hair of smokers but uncorrelated in that of non-smokers, suggesting that cigarette smoke is a common source of toxic elements in humans.

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This multi-site study discusses the content of metals and metalloids (MM) in scalp hair of children, living in different environmental contexts, with the purpose of verifying if hair level of some MM is distinctively gender-specific. A total of 943 hair samples (537 females and 406 males) from adolescents were analyzed for their content of Al, As, Ba, Cd, Co, Cr, Cu, Li, Mn, Mo, Ni, Pb, Rb, Sb, Se, Sr, U, V and Zn. Elemental quantification was performed by ICP-MS. The obtained data identified different metal distributions in adolescent girls which exhibited significantly higher hair concentrations of some trace metals, especially Sr, Zn and Ni, than boys. On the base of the median value, hair of female donors contained 3.8 times more Sr (6.6µg/g) than males (1.7µg/g). Highest concentrations of Zn in females were observed in samples from the mining area of Sardinia (587µg/g). Nickel showed significant differences resulting 2.5-fold higher in female hair. Regardless of the residence site, these elements resulted always significantly different (at p<0.01) between female and male indicating that gender is a confounding factor that has to be more extensively considered for a correct interpretation of metal profiles in human hair.

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The research focus of the present paper was twofold. First, we tried to document that human intake of trace elements is influenced by geological factors of the place of residence. Second, we showed that the elemental composition of human hair is a useful screening tool for assessing people's exposure to potentially toxic substances. For this purpose, we used samples of human hair from adolescents and applied two robust statistical approaches. Samples from two distinct geological and environmental sites were collected: the first one was characterized by the presence of the active volcano Mt. Etna (ETNA group) and the second one lithologically made up of sedimentary rocks (SIC group). Chemical data were statistically processed by Penalized Linear Discriminant Analysis (pLDA) and Discrete AdaBoost (DAB). The separation between the two groups turned out well, with few overlaps accounting for less than 5%. The chemical variables that better distinguished ETNA group from SIC group were As, Cd, Co, Li, Mo, Rb, Sr, U and V. Both pLDA and DAB allowed us to characterize the elements most closely related to the volcanic contribution (As, U and V) and those (Cd, Co, Li, Mo, Rb and Sr) prevalently influenced by the geology of the area where SIC samples were collected. We conclude that the geological characteristics of the area of residence constitute a key factor in influencing the potential exposure to trace elements. Hair analysis coupled with robust statistical methods can be effectively used as a screening procedure to identify areas at great environmental risk.

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Eighty-eight scalp hair samples were collected from Guangzhou (GZ) urban population (15-65 years) to investigate the accumulation of As and other metals (Cr, Mn, Ni, Cu, Zn, Cd, Sn, Sb, Hg and Pb). Demographic information, including body weight, height, age, gender, habits of smoking and drinking, types of drinking water, duration of stay in GZ, days of stay in GZ per year (days/year), and hours spent in indoor environment per day (h/day), were also recorded during hair sampling to refine the uncertainty of risk assessment derived from exposures to elements via dust and airborne particles. No significant non-carcinogenic risk was found. However, the cancer risks of Cr and As for both ingestion and inhalation exceeded the most tolerable regulated level (1.0×10(-6)). The environmental exposures to urban dust and airborne particles were observed significantly correlated to accumulations of Cd (R=0.306, p=0.005) and Ni (R=0.333, p=0.002) in scalp hair. Furthermore, the hair burden of elements was also significantly (p<0.05) dependent on gender (Mn, Ni, Zn, As, Sn and Hg), age (Cr, As, Cd and Hg), duration of stay in GZ (Hg) as well as nutritional and physical status, reflected by BMI and BSA (Cr, Ni, Cd, Sb and Hg). Nutritional and physical status was observed as the exclusive important factor influencing As speciation in human scalp hair. However, habits of smoking and alcohol drinking as well as types of drinking water were not identified as the significant influencing factors on any element (p>0.05).

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This study was undertaken to investigate mineral changes in weathered scalp hair after burial. EDX (energy dispersive X-ray spectroscopy) analysis was performed to measure the presence of minerals on the hair surface. Twelve scalp hairs, buried for 5-40 years, were chosen from deceased individuals buried in tombs in Soha-Ri, Kyonggi-Do, and other regions in Korea. Three normal hairs were used as the control group. EDX data showed that carbon, oxygen, and sulfur were detected in hair collected from all three burial grounds. In contrast, calcium was only detected in hair collected from tombs in Soha-ri. The amounts of calcium and sulfur were found to decrease with time for hair collected from tombs in Soha-ri. Similar results were observed with sodium for hair collected from other regions. These results show region specific mineral detection and a decrease in the concentration of minerals with time. Consequently, it is suggested that changes in minerals concentration in weathered hair could be used as basic data in the field of forensic medicine.

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This study was undertaken to investigate the morphological changes of scalp hair according to weathering after burial and to offer basic data for forensic science. To examine the effect of weathering degree, the 51 human scalp hairs buried after death were taken from deceased individuals in tombs in Korea. The morphological changes in weathering hair shafts of the scalp were investigated using the transmission electron microscopes (TEM). There were little morphological differences of weathering depending on the burial period. The weathering changes includes detachment of cuticle layer, aggregation of macrofibril and hollow formation in the cortex according to the burial period. These results could provide basic data to the field of forensic medicine.

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This study was undertaken to investigate the morphological changes of scalp hair according to weathering after burial and to offer basic data for forensic science. To examine the effect of weathering degree, the 51 human scalp hairs buried after death were taken from deceased individuals in tombs in Korea. The morphological changes in weathering hair shafts of the scalp were investigated using the transmission electron microscopes (TEM). There were little morphological differences of weathering depending on the burial period. The weathering changes includes detachment of cuticle layer, aggregation of macrofibril and hollow formation in the cortex according to the burial period. These results could provide basic data to the field of forensic medicine.

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