Sunscreen photoprotection and vitamin D status.

BACKGROUND: Global concern about vitamin D deficiency has fuelled debates on photoprotection and the importance of solar exposure to meet vitamin D requirements. OBJECTIVES: To review the published evidence to reach a consensus on the influence of photoprotection by sunscreens on vitamin D status, considering other relevant factors. METHODS: An international panel of 13 experts in endocrinology, dermatology, photobiology, epidemiology and biological anthropology reviewed the literature prior to a 1-day meeting in June 2017, during which the evidence was discussed. Methods of assessment and determining factors of vitamin D status, and public health perspectives were examined and consequences of sun exposure and the effects of photoprotection were assessed. RESULTS: A serum level of ≥ 50 nmol L-1 25(OH)D is a target for all individuals. Broad-spectrum sunscreens that prevent erythema are unlikely to compromise vitamin D status in healthy populations. Vitamin D screening should be restricted to those at risk of hypovitaminosis, such as patients with photosensitivity disorders, who require rigorous photoprotection. Screening and supplementation are advised for this group. CONCLUSIONS: Sunscreen use for daily and recreational photoprotection does not compromise vitamin D synthesis, even when applied under optimal conditions. What's already known about this topic? Knowledge of the relationship between solar exposure behaviour, sunscreen use and vitamin D is important for public health but there is confusion about optimal vitamin D status and the safest way to achieve this. Practical recommendations on the potential impact of daily and/or recreational sunscreens on vitamin D status are lacking for healthy people. What does this study add? Judicious use of daily broad-spectrum sunscreens with high ultraviolet (UV) A protection will not compromise vitamin D status in healthy people. However, photoprotection strategies for patients with photosensitivity disorders that include high sun-protection factor sunscreens with high UVA protection, along with protective clothing and shade-seeking behaviour are likely to compromise vitamin D status. Screening for vitamin D status and supplementation are recommended in patients with photosensitivity disorders.

Crocin, a natural molecule with potentially beneficial effects against skin ageing.

OBJECTIVE: Oxidative stress and low-grade chronic inflammation stand out as key features of physiological skin ageing. The aim of this study was to examine in normal human epidermal keratinocytes (NHEK) and human dermal fibroblasts (HDF) grown in vitro, the antioxidant and anti-inflammatory properties of crocin, a carotenoid glycoside responsible for the colour of saffron. Moreover, considering the newly emerging field of skin glycobiology and the presence of two gentiobiosyl moieties in crocin, the effect of crocin on NHEK glycosylation pathways was for the first time investigated. METHODS: The anti-inflammatory and antioxidant activities of crocin were evaluated by in vitro assays of antioxidation activities, ELISA and microarray analysis. The effect of crocin on keratinocyte glycobiology was evaluated by proprietary GLYcoDiag lectin technologies and microarray analysis. RESULTS: Crocin is endowed with antioxidant potential against reactive oxygen species, protects squalene against UVA-induced peroxidation and prevents the release of inflammatory mediators. The expression of NF-kB-related genes and glycosylation-related genes is modulated in the presence of crocin. CONCLUSION: Results could designate this molecule as a promising skin ageing prevention cosmetic agent. Of note, some of these effects could be mediated by protein O-glycosylation and interaction of crocin with osidic receptors of keratinocytes.

Vichy Thermal Spring Water (VTSW), a cosmetic ingredient of potential interest in the frame of skin ageing exposome: an in vitro study.

OBJECTIVE: To study the effects of the very high minerality Vichy Thermal Spring Water (VTSW) on human keratinocytes grown in vitro. METHODS: The effect of VTSW was monitored by full genome transcriptomic technology and immunofluorescence microscopy. RESULTS: In the presence of 50% VTSW, the expression of a number of skin homoeostasis-related genes is increased, specifically with respect to dermal-epidermal junction, epidermal cohesion and communication, keratinocyte proliferation-differentiation balance, antioxidant mechanisms and DNA repair. CONCLUSION: This work suggests that VTSW could be considered as an ingredient of potential interest to address some of the deleterious effects of skin ageing exposome.

Age-dependent changes in eumelanin composition in hairs of various ethnic origins.

Hair pigmentation is one of the most conspicuous phenotypes of humans. From a chemical point of view, however, data remain scarce regarding human hair pigmentation characteristics. To determine melanin content and composition in human eumelanic hair from individuals of different ethnic origins and at different ages, we collected hair from 56 subjects with eumelanic hair from each group of African-American, East Asian, and Caucasian origin. The 56 subjects consist of 14, seven each of males and females, each from four age classes of younger than 11, between 12 and 19, between 20 and 45, and older than 46. We analysed hair colour scale, total melanin value, and contents of pyrrole-2,3,5-tricarboxylic acid (PTCA) and pyrrole-2,3-dicarboxylic acid (PDCA). We measured age-dependent increases in the relative quantity of eumelanin in pigmented human hairs in the three ethnic groups. Regarding melanin composition, we observed an increase in the PDCA/PTCA ratio with age in African-American and Caucasian hairs until approaching the quite constant level of the ratio in East Asian hairs in the elderly individuals. Our results evidence differences in the content and composition of eumelanin in human hair among African-American, Caucasian and East Asian individuals. Furthermore, we show evidence of age-dependent changes in the quantity and quality of eumelanin in pigmented human hairs. In particular, the age-dependent modification of the PDCA/PTCA ratio, a marker for 5,6-dihydroxyindole units in eumelanin, suggests a chronological evolution of hair follicle melanocyte phenotype (e.g. decrease in dopachrome tautomerase expression).

Skin responses to topical dehydroepiandrosterone: implications in antiageing treatment?

BACKGROUND: Although low dehydroepiandrosterone (DHEA) is suspected to have a role in skin ageing, little information is available on the mechanisms potentially involved. OBJECTIVES: To obtain information on androgen receptor (AR) and procollagen expression in ageing skin during DHEA treatment. METHODS: A placebo-controlled, randomized, prospective study was performed with 75 postmenopausal women aged 60-65 years. The women were treated twice daily for 13 weeks with 3·0 mL of placebo or 0·1%, 0·3%, 1% or 2% DHEA cream applied on the face, arms, back of hands, upper chest and right thigh where 2-mm biopsies were collected before and after treatment. RESULTS: Although the overall structure of the epidermis was not significantly affected at the light microscopy level, AR expression examined by immunocytochemistry was markedly increased by DHEA treatment. In the dermis, the expression levels of procollagen 1 and 3 mRNA estimated by in situ hybridization were increased by DHEA treatment. In addition, the expression of heat shock protein (HSP) 47, a molecule believed to have chaperone-like functions potentially affecting procollagen biosynthesis, was also found by immunocytochemistry evaluation to be increased, especially at the two highest DHEA doses. CONCLUSION: These data suggest the possibility that topical DHEA could be used as an efficient and physiological antiageing skin agent.

Chronological ageing of human hair keratin fibres.

Examination of very long hair (length > 2.4 m) using a large range of evaluation methods including physical, chemical, biochemical and microscopic techniques has enabled to attain a detailed understanding of natural ageing of human hair keratin fibres. Scrutinizing hair that has undergone little or no oxidative aggression--because of the absence of action of chemical agents such as bleaching or dyeing--from the root to the tip shows the deterioration process, which gradually takes place from the outside to the inside of the hair shaft: first, a progressive abrasion of the cuticle, whilst the cortex structure remains unaltered, is evidenced along a length of roughly 1 m onwards together with constant shine, hydrophobicity and friction characteristics. Further along the fibre, a significant damage to cuticle scales occurs, which correlates well with ceramides and 18-Methyl Eicosanoic Acid (18-MEA) decline, and progressive decrease in keratin-associated protein content. Most physical descriptors of mechanical and optical properties decay significantly. This detailed description of natural ageing of human hair fibres by a fine analysis of hair components and physical parameters in relationship with cosmetic characteristics provides a time-dependent 'damage scale' of human hair, which may help in designing new targeted hair care formulations.

Human eyelash characterization.

BACKGROUND: Few biological data on human eyelash follicles have been reported in the literature. OBJECTIVES: To characterize eyelash follicle growth, cycle and morphology, and further investigate the biological mechanisms that determine eyelash length, curl and pigmentation, compared with scalp hair follicle. METHODS: Twenty-nine caucasian female volunteers aged between 26 and 60 years were enrolled in the study to provide eyelashes. Four of these volunteers were followed weekly for 9 months to characterize their eyelash cycle. Eyelash length and time of renewal were measured using a high-resolution camera and image analysis. Immunohistological study of the bulbs were performed on eyelid biopsies from 17 patients requiring block excision for ectropion repair. RESULTS: The calculated durations of anagen phase and complete cycle of the eyelashes were 34 + or - 9 and 90 + or - 5 days, respectively. Eyelash follicle growth rate was quite variable, with an average rate of 0.12 + or - 0.05 mm daily. Eyelash follicle morphology was very close to that of the scalp hair follicle, but some remarkable differences were noticed. For example, the K19-positive epithelial stem cell population was spread all along the follicle and not split into two reservoirs as seen in scalp hair follicles. Some asymmetry was detected in HSPG and CSPG, as well as K38 (formerly Ha8) and K82 (formerly Hb2) distribution, similar to that observed in curly hair. Finally, dopachrome tautomerase was found expressed in eyelash follicle melanocytes, while it was strikingly absent in scalp hair follicle melanocytes. CONCLUSIONS: The eyelash is structurally very close to curly hair but some biological processes related to follicle cycle and pigmentation differ markedly.

Evaluation of cytotoxic properties of organometallic ferrocifens on melanocytes, primary and metastatic melanoma cell lines.

Malignant melanoma is one of the most severe forms of skin cancer, and chemotherapeutic agents currently in use are poorly effective in curing the disease. Here we describe the properties of two organometallic ferrocenyl derivatives, ferrocifen (Fc-OH-Tam) and ferrociphenol (Fc-diOH) that show a specific antiproliferative effect on melanoma cells. After a short incubation period, Fc-OH-Tam is highly cytotoxic on melanoma cells but less toxic on melanocytes. Fc-diOH is slightly toxic at a high concentration but no discrepancy is observed between malignant and normal cells. After a long incubation time the latter is highly toxic for malignant cells but not for normal cells while the former was very highly toxic for primary malignant cells and significantly less toxic for normal cells. We also found that oxidative stress is not implicated in the mechanism of cytotoxicity, since both derivatives neither induce reactive oxygen species (ROS) level in melanocytes nor in melanoma cells. Finally, investigation on hair follicle growth revealed that the two organometallic derivatives induced an irreversible ejection of the hair shaft, thus predicting a potential hair loss side effect if used as a chemotherapeutic treatment.

TRP-2 expression protects HEK cells from dopamine- and hydroquinone-induced toxicity.

We previously reported that melanogenic enzyme TRP-2 (or DCT for DOPAchrome tautomerase) expression in WM35 melanoma cells resulted in increased intracellular GSH levels, reduction in DNA damage induced by free radicals, and decreased cell sensitivity to oxidative stress. These effects seemed to depend on a particular cellular context, because none of them were found to occur in HEK epithelial cells. We postulated that the TRP-2 beneficial effect observed in WM35 cells in the oxidative stress situation may relate to quinone metabolization and, more precisely, to the ability of TRP-2 to clear off related toxic metabolites, resulting in a global redox status modification. Here, a comparative protein expression profiling of catecholamine biosynthesis enzymes and detoxification enzymes was conducted in WM35 melanoma cells and in HEK epithelial cells, in comparison with normal human melanocytes. Results showed that WM35 cells, but not HEK cells, expressed enzymes involved in catecholamine biosynthesis, suggesting that their quinone-related toxic metabolites were present in WM35 cells but not in HEK cells. To address the issue of a possible TRP-2 beneficial effect toward quinone toxicity, cell survival experiments were then conducted in HEK cells using dopamine and hydroquinone at toxic concentrations. We showed that TRP-2 expression significantly reduced HEK cell sensitivity to both compounds. This beneficial property of TRP-2 was likely to depend on the integrity of its DOPAchrome tautomerase catalytic site, because both TRP-2(R194Q) and TRP-2(H189G), which have lost their DOPAchrome tautomerase activity, failed to modify the HEK cell response to dopamine and hydroquinone. These results suggest that TRP-2 acts on quinone metabolites other than DOPAchrome, e.g., in the catecholamine pathway, and limits their deleterious effects.

Proteoglycan expression patterns in human hair follicle.

BACKGROUND: Proteoglycans (PGs) are known to play key roles in many cellular signalling pathways involved in hair follicle biology. Although some PG core proteins have previously been described in adult human hair follicles, their glycosaminoglycan (GAG) moieties have been less studied. OBJECTIVES: To add knowledge about PG core protein and GAG distributions in human anagen hair follicle and, for selected follicles, during catagen. METHODS: We used immunohistochemistry and immunohistofluorescence to revisit the expression pattern of GAG chains and core proteins in human hair follicle. The studied epitopes included CD44v3, syndecan-1, perlecan, versican, aggrecan, biglycan, heparan sulphate (HS), chondroitin sulphate (CS), dermatan sulphate (DS) and keratan sulphate (KS). RESULTS: The membrane PGs syndecan-1 and CD44v3 were respectively detected in the epithelial part of whole hair and in the outer root sheath basal layer. The dermal part of the hair follicle contained high amounts of extracellular PGs such as perlecan, versican, aggrecan, biglycan and their saccharidic moieties, namely HS, CS, DS and KS. We also observed a variable distribution of these components along the hair follicle. Especially, we noted a PG impoverishment at the very bottom of the anagen bulb. Moreover, while type D chondroitin expression remained unaffected, 4C3-CS and PG4-CS/DS epitopes respectively decreased in the dermal papilla and the connective tissue sheath, at the onset of catagen. CONCLUSIONS: GAG and PG expression along the human anagen hair follicle was characterized by (i) discontinuities mainly affecting the basement membrane and (ii) disappearance of some epitopes at catagen onset. These results are discussed in term of functionalities in nutrient diffusion, cell proliferation and differentiation, and hair protection.

6-O glucose linoleate supports in vitro human hair growth and lipid synthesis.

The hair follicle is a very active organ with a complex structure, which produces a hair fibre at a rate of 0.3 mm a day. Accordingly, the hair follicle is highly demanding in energy source, as the hair bulb matrix cells are endowed with one of the highest rates of proliferation in the human body. Moreover, recent data have shown the involvement of lipids in hair follicle function. As in vitro-grown hair follicle keeps producing a hair fibre that closely resembles the natural hair fibre, we decided to use this model to investigate the role of a new of glucose linoleate derivative (6-O-linoleyl-d-glucose: 6-O-GL) as a lipid precursor and energy provider. Our results demonstrated that 6-O-GL was (i) quite stable and surprisingly resistant to oxidative degradation, and (ii) readily taken up and metabolized by the hair follicle into various lipids, namely neutral lipids, ceramides and polar lipids. Moreover, it supported hair follicle growth and survival in a glucose- and linoleic-acid free medium. 6-O-GL thus appeared to be a bi-functional nutrient, ensuring both proper fibre quality and production by the hair follicle.

Effect of donepezil on motor and cognitive function in Huntington disease.

Striatal cholinergic dysfunction may be important in Huntington disease (HD). We studied whether donepezil improves chorea, cognition, and quality of life (QoL) in HD. Thirty patients were randomly assigned to treatment with donepezil or placebo. At the doses studied, donepezil did not improve chorea, cognition, or QoL. Adverse events were similar between both groups. Based on this small sample study, donepezil was not an effective treatment for HD.

Protective effects of taurine on human hair follicle grown in vitro.

Taurine is a naturally occurring beta-amino acid produced by methionine and cysteine metabolism. It is involved in a variety of physiological functions, including immunomodulatory and antifibrotic. Taking advantage of the ability of human hair follicle grown in vitro to recapitulate most of the characteristic features of normal hair follicle in vivo, we studied (i) taurine uptake by isolated human hair follicles; (ii) its effects on hair growth and survival rate; and (iii) its protective potential against transforming growth factor (TGF)-beta1, an inhibitor of in vitro hair growth and a master switch of fibrotic program. We showed that taurine was taken up by the connective tissue sheath, proximal outer root sheath and hair bulb, promoted hair survival in vitro and prevented TGF-beta1-induced deleterious effects on hair follicle.

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.

Human hair greying is linked to a specific depletion of hair follicle melanocytes affecting both the bulb and the outer root sheath.

BACKGROUND: Although hair greying is a very common phenomenon characterized by loss of pigment in the hair shaft, the events that cause and control natural hair whitening with age in humans are still unclear. OBJECTIVES: To decipher the origin of natural hair whitening. METHODS: Human hair melanocytes were immunohistochemically characterized at different stages of whitening. RESULTS: Loss of hair shaft melanin was found to be associated with a decrease in both bulb melanin content and bulb melanocyte population. Although few melanocytes were present in the bulbs of grey hair, they still expressed tyrosinase and tyrosinase-related protein-1, synthesized and transferred melanins to cortical keratinocytes as seen by the presence of melanin granules. In white hair bulbs, no melanocytes could be detected either with pMel-17 or vimentin labelling. Pigmented hair follicles are known to contain inactive melanocytes in the outer root sheath (ORS), and grey and white hairs were also found to contain some of these quiescent melanocytes. However, their population was decreased compared with pigmented hair follicles, ranging from small to nil. This depletion of melanocytes in the different areas of white hairs was detected throughout the hair cycle, namely at telogen and early anagen stages. In contrast, the infundibulum and sebaceous gland of both pigmented and white hairs showed a similar distribution of melanocytes. Furthermore, other distinct cell populations located in the ORS, namely putative stem cells, Merkel cells and Langerhans cells were equivalently identified in pigmented and white hairs. CONCLUSIONS: Thus, hair greying appears to be a consequence of an overall and specific depletion of bulb and ORS melanocytes of human hair.

Hair keratin pattern in human hair follicles grown in vitro.

The keratin family includes epithelial (soft) keratins and hair (hard) keratins, and can be divided into acidic type I and basic to neutral type II subfamilies. Recently, nine type I and six type II hair keratin genes have been characterized through the screening of a human PAC library. The expression of these genes in the hair follicle was determined in vivo and a combined catalog of acidic and basic hair keratins was established. In this study, we investigated the expression and localization of most of the human hair keratin members of both types in human hair grown in vitro. We show that in vitro growth of hair follicles for 10 days in complete William's E culture medium did not alter the expression pattern of hair keratins. Similarly to the in vivo situation, each hair keratin was localized in precise and discrete compartments of the follicle, ranging from the matrix to the upper cortex and/or the hair cuticle. This study shows that the increase in length of in vitro grown follicles was accompanied by the proper hair shaft keratinization process. It also shows that hair follicle integrity was maintained in vitro, both in terms of gross morphology and molecular organization despite the complexity of the keratin expression pattern.

What is the 'true' function of skin?

Conventional textbook wisdom portrays the skin as an organ that literally enwraps whatever each of us stands for as a more or less functional, individual member of the mammalian species, and has it that the skin primarily establishes, controls and transmits contacts with the external world. In addition, the skin has long been recognized to protect the organism from deleterious environmental impacts (physical, chemical,microbiological), and is well-known as crucial for the maintenance of temperature, electrolyte and fluid balance. Now, ever more studies are being published that show the skin to also operate as a huge and highly active biofactory for the synthesis,processing and/or metabolism of an astounding range of e.g. structural proteins, glycans, lipids and signaling molecules. Increasingly, it becomes appreciated that the skin, furthermore, is an integral component of the immune, nervous and endocrine systems, with numerous lines of cross-talk between these systems established intracutaneously (e.g. Ann NY Acad Sci Vol 885, 1999; Endocrine Rev 21:457-487, 2000; Physiol Rev 80:980-1020, 2001; Exp Dermatol 10: 349-367, 2001). All these emerging cutaneous functions beyond the classical image of the skin as a barrier and sensory organ are immediately relevant for many of the quandaries that clinical dermatology, dermatopathology, and dermatopharmacology are still struggling with to-date, and offer the practising dermatologist attractive new targets for therapeutic intervention. Yet, many of these skin functions are not even mentioned in dermatology textbooks and await systematic therapeutic targeting. Following a suggestion by Enno Christophers, the current 'Controversies' feature brings together an unusually diverse council of biologists and clinicians, who share their thought-provoking views with the readers and allow us to peek into the future of research in cutaneous biology, not the least by reminding us of the -- often ignored -- evolutionary and embryonal origins of our favorite organ. Hopefully, this unique discussion feature will foster an understanding of the 'true' skin functions that is both more comprehensive and more profound than conventional teaching on this topic, and will stimulate more than 'skin-deep' reflections on the full range of skin functions.

Type-1 steroid 5 alpha-reductase is functionally active in the hair follicle as evidenced by new selective inhibitors of either type-1 or type-2 human steroid 5 alpha-reductase.

Steroid 5 alpha-reductase catalyzes the reduction of testosterone (T) into the very potent androgen dihydrotestosterone (DHT). The different tissue expression patterns of the two isoforms of 5 alpha-reductase, namely type-1 and type-2 5 alpha-reductase (5 alpha-R1 and 5 alpha-R2, respectively), have prompted studies directed towards the synthesis of selective 5 alpha-R1 or 5 alpha-R2 inhibitors. In this present work, we have performed a structure/activity study on the inhibitory potential of indole carboxylic acids against hair follicle 5 alpha-reductase activity. We have demonstrated that this class of molecules were potent inhibitors of either 5 alpha-R1 or 5 alpha-R2 or both depending on (i) substituents in positions 4, 5 or 6 and (ii) the presence of a free carboxylic group. We have also found that only 5 alpha-R1 or 5 alpha-R1/R2 inhibitors were able to inhibit 5 alpha-reductase activity in plucked hairs from female volunteers or in freshly isolated female hair follicles, selective 5 alpha-R2 inhibitors being inactive.

The follicular automaton model: effect of stochasticity and of synchronization of hair cycles.

Human scalp hair consists of a set of about 10(5)follicles which progress independently through developmental cycles. Each hair follicle successively goes through the anagen (A), catagen (C), telogen (T) and latency (L) phases that correspond, respectively, to growth, arrest and hair shedding before a new anagen phase is initiated. Long-term experimental observations in a group of ten male, alopecic and non-alopecic volunteers allowed determination of the characteristics of hair follicle cycles. On the basis of these observations, we previously proposed a follicular automaton model to simulate the dynamics of human hair cycles and the development of different patterns of alopecia [Halloy et al. (2000) Proc. Natl Acad. Sci. U.S.A.97, 8328-8333]. The automaton model is defined by a set of rules that govern the stochastic transitions of each follicle between the successive states A, T, L and the subsequent return to A. These transitions occur independently for each follicle, after time intervals given stochastically by a distribution characterized by a mean and a standard deviation. The follicular automaton model was shown to account both for the dynamical transitions observed in a single follicle, and for the behaviour of an ensemble of independently cycling follicles. Here, we extend these results and investigate additional properties of the model. We present a deterministic version of the follicular automaton. We show that numerical simulations of the stochastic version of the automaton yield steady-state level of follicles in the different phases which approach the levels predicted by the deterministic equations as the number of follicles progressively increases. Only the stochastic version can successfully reproduce the fluctuations of the fractions of follicles in each of the three phases, observed in small follicle populations. When the standard deviation is reduced or when the follicles become otherwise synchronized, e.g. by a periodic external signal inducing the transition of anagen follicles into telogen phase, large-amplitude oscillations occur in the fractions of follicles in the three phases. These oscillations are not observed in humans but are reminiscent of the phenomenon of moulting observed in a number of mammalian species.

Ceramide binding to African-American hair fibre correlates with resistance to hair breakage.

Repetitive hair-relaxing treatments often applied to African-American hair weaken the hair structure. Therefore hair breakage is a common feature of African-American hair and an important cause of hair loss. Recently, by analysing the lipids extracted from human hair, a fraction of free-ceramide was isolated in which sphinganine was predominant. This study shows that this sphinganine-derived ceramide (i.e. C18-dhCer) binds to African-American hair and protects it from weakening caused by chemicals. To show this binding, we used two methods: radioactivity detection with a microimager and secondary ion mass spectrometry. We evaluated the benefits of C18-dhCer on African-American hair fibre, relaxed by guanidine hydroxide, using a new method called the Break'in Brush Technique (BBT). This method determines the hair breakage resistance during a brushing. Using this technique, we have shown less breakage when applying a shampoo with ceramide. The present study opens new prospects for the development of products able to increase the protection, provide better care and meet the needs of African-American hair thanks to the effect of ceramide binding.