Selenium disulfide: a key ingredient to rebalance the scalp microbiome and sebum quality in the management of dandruff.

BACKGROUND: Dandruff is a chronic and relapsing scalp condition characterized by flaky scalp. Environmental and host factors (exposome) may alter the sebaceous gland activity, sebum composition, epidermal barrier function, and scalp microbiome balance, resulting in dandruff. Selenium disulfide (SeS2) improves the clinical signs of dandruff. OBJECTIVES: To investigate the mode of action of SeS2 shampoo during treatment and relapse phases. MATERIALS & METHODS: Two single-center studies assessed dandruff severity, subjective efficacy perception, microbial balance, microbiota diversity and sebum lipids. RESULTS: SeS2 significantly (p≤0.01) reduced scaling and led to a significant decrease of Malassezia and Staphylococcus spp. counts in both lesional and non-lesional areas, compared to the vehicle at D28 returning to baseline levels at D56. Cutibacterium spp. levels were not different between the SeS2 and the vehicle treatment groups but had significantly increased with SeS2 (p<0.001) in the lesional zone at D56. The ratio Malassezia spp./Cutibacterium spp. decreased significantly in lesional zones compared to baseline levels, at both D28 and D35 (p<0.001). The total squalene content significantly increased (p<0.05), whereas peroxided squalene had significantly decreased by almost 50% at D31. The ratio triglycerides/free fatty acids significantly (p<0.0001) increased, almost 5-fold, between D0 and D31. SeS2 shampoo was very well tolerated. CONCLUSION: SeS2 is beneficial in scalp dandruff, even after treatment interruption. It is well tolerated, rebalances the equilibrium between the main bacterial and fungal populations, and improves sebum quality.

In vivo multiphoton imaging for non-invasive time course assessment of retinoids effects on human skin.

BACKGROUND: In vivo multiphoton imaging and automatic 3D image processing tools provide quantitative information on human skin constituents. These multiphoton-based tools allowed evidencing retinoids epidermal effects in the occlusive patch test protocol developed for antiaging products screening. This study aimed at investigating their relevance for non-invasive, time course assessment of retinoids cutaneous effects under real-life conditions for one year. MATERIALS AND METHODS: Thirty women, 55-65 y, applied either retinol (RO 0.3%) or retinoic acid (RA 0.025%) on one forearm dorsal side versus a control product on the other forearm once a day for 1 year. In vivo multiphoton imaging was performed every three months, and biopsies were taken after 1 year. Epidermal thickness and dermal-epidermal junction undulation were estimated in 3D with multiphoton and in 2D with histology, whereas global melanin density and its z-epidermal distribution were estimated using 3D multiphoton image processing tools. RESULTS: Main results after one year were as follows: a) epidermal thickening with RO (+30%); b) slight increase in dermal-epidermal junction undulation with RO; c) slight decrease in 3D melanin density with RA; d) limitation of the melanin ascent observed with seasonality and time within supra-basal layers with both retinoids, using multiphoton 3D-melanin z-epidermal profile. CONCLUSIONS: With a novel 3D descriptor of melanin z-epidermal distribution, in vivo multiphoton imaging allows demonstrating that daily usage of retinoids counteracts aging by acting not only on epidermal morphology, but also on melanin that is shown to accumulate in the supra-basal layers with time.

Vitamin C Prevents Ultraviolet-induced Pigmentation in Healthy Volunteers: Bayesian Meta-analysis Results from 31 Randomized Controlled versus Vehicle Clinical Studies.

Background: Repeated nonextreme sun exposures induce skin pigmentation by increasing melanin production and by oxidizing preexisting melanin and melanin precursors. This leads to skin disorders and skin color heterogeneity such as hyperpigmented spots. Objective: We assessed 31 randomized, controlled clinical trials to determine the potential of vitamin C to limit ultraviolet (UV) daylight-induced pigmentation, considering dose response and different skin type populations (Caucasian and Chinese). Materials and Methods: Thirty-one intraindividual, randomized, controlled clinical trials involving Caucasian and Chinese subjects (15-35 healthy male or female volunteers per study, 741 total volunteers) 18 to 50 years of age with Phototype III and individual typology angle (ITA) value between 28 and 49 degrees were analyzed. The 31 studies assessed the potential of vitamin C (formulated with the copolymer Styrène-Anhydride Maléique [SMA]) to decrease pigmentation induced by UV daylight exposure. Results were combined using a Bayesian meta-analysis to provide probabilistic evidence of the effects of vitamin C by dose and population. Results: Vitamin C was effective in reducing pigmentation induced by UV daylight-simulated expositions (4 days at 0.75 Individual Minimal Erythemal Dose [MEDi]) in a dose-dependent manner. During the depigmentation phase, no additive value was provided by the vitamin C, suggesting that the lightening properties described in the literature for vitamin C correspond to an antipigmenting quality rather than a depigmenting effect. Conclusion: Vitamin C is a valuable and safe dermocosmetic antipigmenting compound with a strong effect at 10% possibly useful in preventing signs of photoaging.

Comparison of Healthy and Dandruff Scalp Microbiome Reveals the Role of Commensals in Scalp Health.

Several scalp microbiome studies from different populations have revealed the association of dandruff with bacterial and fungal dysbiosis. However, the functional role of scalp microbiota in scalp disorders and health remains scarcely explored. Here, we examined the bacterial and fungal diversity of the scalp microbiome and their potential functional role in the healthy and dandruff scalp of 140 Indian women. Propionibacterium acnes and Staphylococcus epidermidis emerged as the core bacterial species, where the former was associated with a healthy scalp and the latter with dandruff scalp. Along with the commonly occurring Malassezia species (M. restricta and M. globosa) on the scalp, a strikingly high association of dandruff with yet uncharacterized Malassezia species was observed in the core mycobiome. Functional analysis showed that the fungal microbiome was enriched in pathways majorly implicated in cell-host adhesion in the dandruff scalp, while the bacterial microbiome showed a conspicuous enrichment of pathways related to the synthesis and metabolism of amino acids, biotin, and other B-vitamins, which are reported as essential nutrients for hair growth. A systematic measurement of scalp clinical and physiological parameters was also carried out, which showed significant correlations with the microbiome and their associated functional pathways. The results point toward a new potential role of bacterial commensals in maintaining the scalp nutrient homoeostasis and highlights an important and yet unknown role of the scalp microbiome, similar to the gut microbiome. This study, therefore, provides new perspectives on the better understanding of the pathophysiology of dandruff.

Exploration of scalp surface lipids reveals squalene peroxide as a potential actor in dandruff condition.

Dandruff is a common but complex disorder with three major contributing factors: (1) individual predisposition, (2) scalp sebum and (3) Malassezia yeast colonization. To obtain further insights into the role of sebum in dandruff biogenesis, we analyzed scalp lipid species in a cohort of ten dandruff-free (control) and ten dandruff-afflicted volunteers by gas chromatography coupled to mass spectrometry. Lipid peroxidation levels and biochemical markers of oxidative stress were also assessed. Squalene, a major sebum component, was significantly more peroxidized in dandruff-affected scalps, resulting in significantly higher ratios of squalene monohydroperoxide (SQOOH)/squalene. This was observed when comparing dandruff-affected zones of dandruff subjects to both their non-affected zones and control subjects. In addition, other biomarkers such as malondialdehyde indicated that oxidative stress levels were raised on dandruff scalps. Surprisingly, differences regarding either free or bound fatty acids were fairly rare and minor. Certain novel findings, especially squalene peroxidation levels, were then confirmed in a validation cohort of 24 dandruff-affected subjects, by comparing dandruff-affected and non-dandruff zones from the same individuals. As SQOOH can induce both keratinocyte inflammatory responses and hyperproliferation in vitro, we hypothesized that increased SQOOH could be considered as a new etiological dandruff factor via its ability to impair scalp barrier function. Our results also indicated that Malassezia could be a major source of squalene peroxidation on the scalp.