Preservatives are added to products for two reasons: first, to prevent microbial spoilage and therefore to prolong the shelf life of the product; second, to protect the consumer from a potential infection. Although chemical preservatives prevent microbial growth, their safety is questioned by a growing segment of consumers. Therefore, there is a considerable interest in the development of preservative-free or self-preserving cosmetics. In these formulations traditional/chemical preservatives have been replaced by other cosmetic ingredients with antimicrobial properties that are not legislated as preservatives according to the Annex VI of the Commission Directive 76/768/EEC and the amending directives (2003/15/EC, 2007/17/EC and 2007/22/EC). 'Hurdle Technology', a technology that has been used for the control of product safety in the food industry since 1970s, has also been applied for the production of self-preserving cosmetics. 'Hurdle Technology' is a term used to describe the intelligent combination of different preservation factors or hurdles to deteriorate the growth of microorganisms. Adherence to current good manufacturing practice, appropriate packaging, careful choice of the form of the emulsion, low water activity and low or high pH values are significant variables for the control of microbial growth in cosmetic formulations. This paper describes the application of the basic principles of 'Hurdle Technology' in the production of self-preserving cosmetics. Multifunctional antimicrobial ingredients and plant-derived essential oils and extracts that are used as alternative or natural preservatives and are not listed in Annex VI of the Cosmetic Directive are also reported.

The development of normal patterns along the primary and secondary vertebrate axes depends on the regularity of early Hox gene expression. During initial stages, these expression events form a sequential pattern of partially overlapping domains along the anteroposterior axis in coincidence with the 3' to 5' order of the genes in the Hox cluster (spatial collinearity). In addition, the genes are activated one after the other in the 3' to 5'order (temporal collinearity). These features are poorly understood within the framework of Molecular Genetics. A model was proposed according to which physical forces act on Hox clusters as a result of signaling from morphogen gradients. The model can explain the collinearity of Hox gene expression along the primary and secondary body axes. The increase in the concentration of morphogen is accordingly followed by an increase of the force acting on the cluster. The genes are sequentially translocated, in the 3' to 5' order, toward the interchromosome domain where they are exposed to transcription factors for activation. The above geometrodynamic approach reproduces most collinearity data. Recent experiments verify the above prediction of sequential 3' to 5' Hox gene translocations in the interchromosome domain. Furthermore, it seems that these translocations, combined with cluster decondensations, are caused by attractive forces acting on the 3' end of the cluster and pulling the genes out of the chromosome territory. Additional experiments are proposed in order to specify the origin of the forces.

In vitro data suggest that different in vivo performances are expected for two dihydroxyacetone (DHA)-containing formulations with similar concentrations of DHA and excipients but different commercially available rheology modifiers: one with a cationic polymer-based rheology modifier (blend) [dimethylacrylamide/ethyltrimonium chloride methacrylate copolymer (and) propylene glycol dicaprylate/dicaprate (and) PPG-1 trideceth-6 (and) C10-11 isoparaffin]; and the other with a polyacrylamide-based rheology modifier (blend) [polyacrylamide (and) C13-14 isoparaffin (and) laureth-7]. Both rheology modifiers (blends) contained comparable levels of polymers and were used at 3% w/w (as supplied). Differences in color development were illustrated in vitro with respect to the yellow/red and lightness/chroma parameters, which were confirmed in the followup in vivo studies. The test article with the cationic polymer-based rheology modifier produced a more natural sunless tan, comparable to a desirable sun-induced tan, for all panelists, one that was more uniform and lasted longer compared with the sunless tan generated by the test article with the polyacrylamide-based rheology modifier. A method for HPLC analysis of DHA in sunless tanning formulations was established and utilized to confirm concentrations of DHA in test articles.pp. 85-105 Basic optics of effect materials by S. A. Jones: BASF Corporation,

In both invertebrates and vertebrates, a set of homeobox genes is involved in the primary pattern formation along the anterior-posterior axis of the developing organism. In particular, the genes of the Hox/HOM complex are located in a physical order in the 3' to 5' direction of the gene clusters. Furthermore, the vertebrate genes of the Hoxa and Hoxd clusters are expressed following the empirical rules of temporal and spatial collinearities: the genes are expressed one after the other according to their positional order and their domains of expression start anteriorly and move gradually towards more posterior locations along the developmental axis. The mechanism that controls this remarkable expression behaviour remains elusive. A proposed morphogen gradient model could justify the serial gene expression in space and time during vertebrate limb development. It is therefore likely that a morphogen concentration ordering might cause the sequential gene expression. I put forward this hypothesis and explore some possibilities that concentration-dependent physical forces might push the Hoxa,d clusters to an environment where the transcriptional activity of the genes is possible. The suggested mechanisms offer satisfactory concentration resolution for differential gene expression. Some experiments are proposed to test the presence of such forces. The verification of this hypothesis would provide a solution to the interpretation problem of the positional information theory in development. Furthermore, it would broaden our knowledge of how gene transcription can be triggered.

The features of spatial and temporal Hox gene collinearity along the anteroposterior and secondary axes of vertebrate development have been extensively studied. However, the understanding of these features remains problematic. Some genetic engineering experiments were performed and the consequent modifications of the Hoxd gene expressions in the vertebrate limb and trunk were presented. A two-phases model was proposed to describe the above results but still many data cannot be explained. In the present work a different mechanism is put forward in order to deal with the above experiments. This alternative mechanism (coined biophysical model), is based on the hypothesis that physical forces decondense and 'loop out' the chromatin fiber causing the observed Hox gene collinearity phenomena at the early stages of axonal development. The two models are compared in detail. The biophysical model adequately explains the data even in cases where the results are characterized as unexpected. Furthermore, the biophysical model predicts that the Hox gene expressions are entangled in space and time and this coupling is compatible with the data of the early developmental stages. Additional experiments are proposed for a direct test of this model.