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The UVA-attenuating properties of the three UVA filters butyl methoxy dibenzoyl methane (BMDBM), methylene bis-benzotriazolyl tetramethylbutylphenol (MBBT), and microfine zinc oxide (ZnO), are compared. For this purpose persistent pigment darkening (PPD) as an in vivo method as well as different in vitro approaches like the UVA/UVB ratio, the critical wavelength, and the Australian standard have been used. For the case of the UVA/UVB ratio and the critical wavelength the behaviour was also assessed after irradiation with 10 minimal erythemal doses (MED). Sunscreen formulations were manufactured containing either one of these UVA filters or combinations of one UVA filter and a constant amount of UVB filter. The concentration of the respective UVA filter was varied. BMDBM was dissolved in the oil phase of the formulations. MBBT, which is produced as particulate organic UVA-filter dispersion with average particle size smaller than 200 nm, was added to the aqueous phase. The microfine ZnO was incorporated into the oil phase. If no additional UVB filters were present, UVA/UVB ratio and critical wavelength stayed almost constant, independent of UVA-filter content. With constant levels of additional UVB filters these parameters increased with UVA-filter concentration. In contrast to the behaviour of the UVA/UVB ratio, which appeared to be a sensitive measure for the UVA protection in relation to UVB protection in almost the whole ranges of UVA-filter concentrations, the critical wavelength approached saturation already at low UVA-filter levels. The UVA-protection factors (UVA-PF) obtained from the in vivo studies increased with the concentration of the UVA filter in the formulations. Formulations, which showed UVA-PFs > or = 4 in most cases met also the conditions of the Australian Standard. An irradiation dose of 2.5 kJ m(-2) (10 MED) induced significant decreases of UVA/UVB ratio or critical wavelength only with some BMDBM formulations, indicating a loss of UVA protection in those cases.

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Both academia and dermatological and cosmetic industries have acknowledged that healthy skin microbiota contribute to overall skin integrity and well-being. This implies that formulations developed for personal care (skin, scalp, hair etc) or (medical and cosmetic) treatment need to be compatible with microbiota conservation or possibly even improvement. The various chemical and biological components and mixtures thereof intended for direct application to the skin should not extensively affect the qualitative and quantitative composition of the skin microbiota. A compound should promote beneficial microbes and inhibit pathogens. Compounds but also final products could be considered at least theoretically “microbiome friendly” while in some cases changes to the microbiota may even be considered beneficial. An important hurdle lies in the practical and methodological approaches to be used for defining microbiota inertia of compounds and formulations. Clear guidelines for assessing microbiome friendliness are lacking. We propose three testing concepts that may help to define microbiome friendliness based on the assessment of minimal microbiota perturbation and possibly elimination of potential pathogens. Methods to prove microbiome friendliness should ultimately be based upon (metagenomic rather than amplicon-based) next generation sequencing of naive versus compound- or final product-exposed skin microbiota in vivo, but preferably also including in vitro and ex vivo pre-screening methodologies to build an understanding of their consequences. As in many domains of microbiome research, the development of experimental process controls and internal standards, which are essentially lacking to date, should be taken as a future prerequisite. There is also a requirement from regulatory agencies to define and harmonize acceptance criteria.