Compositional Variations between Adult and Infant Skin Microbiome: An Update.

Human skin and its commensal microbiome form the first layer of protection to the outside world. A dynamic microbial ecosystem of bacteria, fungi and viruses, with the potential to respond to external insult, the skin microbiome has been shown to evolve over the life course with an alteration in taxonomic composition responding to altered microenvironmental conditions on human skin. This work sought to investigate the taxonomic, diversity and functional differences between infant and adult leg skin microbiomes. A 16S rRNA gene-based metataxonomic analysis revealed significant differences between the infant and adult skin groups, highlighting differential microbiome profiles at both the genus and species level. Diversity analysis reveals differences in the overall community structure and associated differential predicted functional profiles between the infant and adult skin microbiome suggest differing metabolic processes are present between the groups. These data add to the available information on the dynamic nature of skin microbiome during the life course and highlight the predicted differential microbial metabolic process that exists on infant and adult skin, which may have an impact on the future design and use of cosmetic products that are produced to work in consort with the skin microbiome.

Role of pH in skin cleansing.

BACKGROUND: The importance of maintaining the acid-mantle of human stratum corneum to maintain its healthy barrier and skin's biological functions such as desquamation and lipid biosynthesis is well recognized in the literature. An outcome of this has been an increase in the number of skincare products formulated at or near the skin pH with an implication that a product formulated at skin pH will be good for skin. Such an assumption often does not take into account the specific interactions of ingredients in the product with the stratum corneum under skin pH conditions. OBJECTIVE: The objective of this research was to determine whether a skin cleansing product by virtue of its pH being same as "skin pH" is milder to skin. METHODS: A well established Forearm Controlled Application Test (FCAT) protocol was used in clinical studies to compare "skin pH" cleansing systems with neutral pH cleansing systems. Specifically, certain commercially available "skin pH" cleansing bars were compared with a neutral pH syndet bar in two separate FCAT studies. Since these bars differed in their surfactant composition, in a separate FCAT study, two identical prototype bar formulations differed only in their pH were compared. Additionally, two body wash liquid prototypes, identical in composition but differing only in their pH were also compared in another FCAT study. RESULTS: The results obtained showed that skin-cleansing systems formulated solely or predominantly with anionic surfactants under skin pH conditions can result in increased skin dryness and irritation compared to those under neutral pH conditions. The results are explained in terms of the increased electrostatic interaction of anionic surfactants with stratum corneum under low pH conditions compared to neutral pH conditions. CONCLUSION: Skin-cleansing systems formulated solely or predominantly with anionic surfactants under skin pH conditions can result in increased skin dryness and irritation compared to those under neutral pH conditions. Any skin cleansing product by virtue of its pH being same as that of "skin pH" does not guarantee that it will be good for skin. The mildness of a cleanser will be determined by the interactions of its surfactants and other ingredients with stratum corneum under its formulated pH conditions.

CONTEXTE: l'importance de la protection du manteau acide de la couche cornée humaine en vue de maintenir une barrière saine et les fonctions biologiques de la peau, telles que la desquamation et la biosynthèse lipidique, est bien reconnue dans la littérature médicale. Cela a eu pour résultat l'augmentation du nombre de produits cosmétiques formulés à un pH proche ou identique au pH de la peau, impliquant ainsi qu'un produit formulé au pH de la peau sera bon pour la peau. Cette hypothèse ne tient souvent pas compte des interactions spécifiques des ingrédients du produit avec la couche cornée dans des conditions de pH de la peau. OBJECTIF: l'objectif de cette recherche était de déterminer si un nettoyant pour la peau formulé à un pH identique au « pH de la peau ¼ est, pour cette raison, plus doux pour la peau. MÉTHODES: un protocole bien établi de test d'application contrôlée sur l'avant-bras (Forearm Controlled Application Test, FCAT) a été utilisé dans des études cliniques pour comparer les nettoyants à « pH de la peau ¼ et les nettoyants à pH neutre. Plus précisément, certains savons à « pH de la peau ¼ disponibles dans le commerce ont été comparés à un savon surgras à pH neutre dans deux études distinctes faisant appel au FCAT. La composition en termes d'agents de surface de ces savons étant différente, une étude distincte faisant appel au FCAT a comparé deux prototypes de savons de composition identique mais de pH différent. De plus, deux prototypes de savon liquide pour le corps, de composition identique mais de pH différent, ont également été comparés dans une autre étude faisant appel au FCAT. RÉSULTATS: les résultats obtenus ont montré que les nettoyants pour la peau formulés uniquement ou principalement avec des agents de surface anioniques dans des conditions de pH de la peau peuvent entraîner une augmentation de la sécheresse et de l'irritation cutanées, par rapport à ceux formulés dans des conditions de pH neutre. Les résultats s'expliquent par l'interaction électrostatique accrue des agents de surface anioniques avec la couche cornée dans des conditions de pH faible par rapport aux conditions de pH neutre. CONCLUSION: les nettoyants pour la peau formulés uniquement ou principalement avec des agents de surface anioniques dans des conditions de pH de la peau peuvent entraîner une augmentation de la sécheresse et de l'irritation cutanées, par rapport à ceux formulés dans des conditions de pH neutre. La formulation d'un nettoyant pour la peau à un pH identique au « pH de la peau ¼ ne garantit pas qu'il sera bon pour la peau. La douceur d'un nettoyant sera déterminée par les interactions de ses agents de surface et de ses autres ingrédients avec la couche cornée dans ses conditions de formulation en termes de pH.

Efficient control of the rheological and surface properties of surfactant solutions containing C8-C18 fatty acids as cosurfactants.

Systematic experimental study is performed about the effects of chain length (varied between C8 and C18) and concentration of fatty acids (FAc), used as cosurfactants to the mixture of the anionic surfactant SLES and the zwitterionic surfactant CAPB. The following properties are studied: bulk viscosity of the concentrated solutions (10 wt % surfactants), dynamic and equilibrium surface tensions, surface modulus, and foam rheological properties for the diluted foaming solutions (0.5 wt % surfactants). The obtained results show that C8-C10 FAc induce formation of wormlike micelles in the concentrated surfactant solutions, which leads to transformation of these solutions into viscoelastic fluids with very high apparent viscosity. The same FAc shorten the characteristic adsorption time of the diluted solutions by more than 10 times. In contrast, C14-C18 FAc have small effect on the viscosity of the concentrated solutions but increase the surface modulus above 350 mN/m, which leads to higher friction inside sheared foams and to much smaller bubbles in the formed foams. The intermediate chain C12 FAc combines some of the properties seen with C10 FAc and other properties seen with C14 FAc. These results clearly demonstrate how appropriate cosurfactants can be used for efficient control of the rheological properties of concentrated surfactant solutions and of some important foam attributes, such as bubble size and foam rheology.

Spectral bidirectional reflectance distribution function measurements on well-defined textured surfaces: direct observation of shadowing, masking, inter-reflection, and transparency effects.

We present results for the bidirectional reflectance distribution function (BRDF) for samples of uniform rectangular and triangular grooves constructed from polydimethylsilicone replicas. The measurements are performed with the detector in the plane of incidence, but with varying groove orientations with respect to that plane. The samples are opaque in some cases and semitransparent in others. By measuring the BRDF for colored samples over a wide spectral range, we explicitly probe the effect of sample albedo, which is important for inter-reflections. For the opaque samples, we compare the results with exact theoretical results either taken from the literature (for the triangular geometry) or worked out here (for the rectangular geometry). For both geometries, we also extend the theoretical results to finite length grooves. There is generally very good agreement between theory and the experiment. Shadowing, masking, and inter-reflection are clearly observed, as well as effects that may be due to polarization and asperity scattering. For semitransparent samples, we observe the effect of increasing transparency on the BRDF.

Microrheology of cross-linked polyacrylamide networks.

Experiments investigating the local viscoelastic properties of a chemically cross-linked polymer are performed on polyacrylamide solutions in the sol and the gel regimes using polystyrene beads of varying sizes and surface chemistry as probes. The thermal motions of the probes are measured to obtain the elastic and viscous moduli of the sample. Probe dynamics are measured using two different dynamic light scattering techniques, diffusing wave spectroscopy (DWS) and quasielastic light scattering (QELS) as well as video-based particle tracking. Diffusing wave spectroscopy probes the short-time dynamics of the scatterers while QELS measures the dynamics at larger times. Video-based particle tracking provides a way to investigate the local environment of the individual probe particles. A combination of all the techniques results in a larger range of frequencies that can be probed compared to conventional bulk measurements while providing local information at the level of individual probes. A modified algebraic form of the generalized Stokes-Einstein equation is used to calculate the frequency-dependent moduli. A comparison of microrheological measurements with bulk rheology exhibits striking similarity, confirming the applicability of microrheology for chemically cross-linked polymeric systems.

Microrheology of polyethylene oxide using diffusing wave spectroscopy and single scattering.

Experiments investigating the local viscoelastic properties of a simple uncross-linked flexible polymer are performed on polyethylene oxide solutions in the semidilute regime using polystyrene beads of varying sizes and surface chemistry as probes. We measure the thermal motions of the beads to obtain the elastic and viscous moduli of our sample. Two different dynamic light scattering techniques, diffusing wave spectroscopy and quasielastic light scattering (QELS), are used to determine the dynamics of the probe particles. Diffusing wave spectroscopy probes the short time dynamics of the scatterers while QELS or single scattering measures the dynamics at larger times. This results in a larger frequency overlap of the data obtained from the microrheological techniques with the data obtained from the conventional bulk measurements. The moduli are estimated using a modified algebraic form of the generalized Stokes-Einstein equation. Comparison of microrheology with bulk measurements shows excellent similarity confirming the applicability of this method for simple, uncross-linked polymeric systems.