Deposition of plant lipids after single application of a lip care product determined by confocal raman spectroscopy, corneometry and transepidermal water-loss

Novel aspects of Raman spectroscopy in skin research

The analytical technology of Raman spectroscopy has an almost 100‐year history. During this period, many modifications and developments happened in the method like discovery of laser, improvements in optical elements and sensitivity of spectrometer and also more advanced light detection systems. Many types of the innovative techniques appeared (e.g. Transmittance Raman spectroscopy, Coherent Raman Scattering microscopy, Surface‐Enhanced Raman scattering and Confocal Raman spectroscopy/microscopy). This review article gives a short description about these different Raman techniques and their possible applications. Then, a short statistical part is coming about the appearance of Raman spectroscopy in the scientific literature from the beginnings to these days. The third part of the paper shows the main application options of the technique (especially confocal Raman spectroscopy) in skin research, including skin composition analysis, drug penetration monitoring and analysis, diagnostic utilizations in dermatology and cosmeto‐scientific applications. At the end, the possible role of artificial intelligence in Raman data analysis and the regulatory aspect of these techniques in dermatology are briefly summarized. For the future of Raman Spectroscopy, increasing clinical relevance and in vivo applications can be predicted with spreading of non‐destructive methods and appearance with the most advanced instruments with rapid analysis time.

Stratum corneum occlusion induces water transformation towards lower bonding state: a molecular level in vivo study by confocal Raman microspectroscopy

OBJECTIVE

It is conventionally understood that occlusive effects are the retention of excessive water in the stratum corneum (SC), the increase of SC thickness (swelling) and a decrease of the transepidermal water loss. However, the influence of occlusion on water binding properties in the SC is unknown.

METHODS

The action of plant-derived jojoba and almond oils, as well as mineral-derived paraffin oil and petrolatum topically applied on human skin, is investigated in vivo using confocal Raman microspectroscopy. To understand the oils' influence on the SC on the molecular level, the depth-dependent hydrogen bonding states of water in the SC and their relationship to the conformation of keratin, concentration of natural moisturizing factor (NMF) molecules and lipid organization were investigated.

RESULTS

A significant SC swelling was observed only in petrolatum-treated skin. The water concentration was increased in oil-treated skin in the intermediate SC region (40-70% SC depth). Meanwhile, the amount of free, weakly and tightly bound water increased, and strongly bound water decreased in the uppermost SC region (0-30% SC depth). The NMF concentration of oil-treated skin was significantly lower at 50-70% SC depth. The lateral organization of lipids in oil-treated skin was lower at 0-30% SC depth. The secondary structure of keratin was changed towards an increase of β-sheet content in mineral-derived oil-treated skin and changed towards an increase of α-helix content in plant-derived oil-treated skin.

CONCLUSION

The occlusive properties can be summarized as the increase of free water and the transformation of water from a more strongly to a more weakly hydrogen bonding state in the uppermost SC, although some oils cause insignificant changes of the SC thickness. The accompanied changes in the keratin conformation at the intermediate swelling region of the SC also emphasize the role of keratin in the SC's water-transporting system, that is the water in the SC transports intercellularly and intracellularly in the intermediate swelling region and only intercellularly in the uppermost non-swelling region. Bearing this in mind, almond, jojoba and paraffin oils, which are not occlusive from the conventional viewpoint, have an occlusion effect similar to petrolatum on the SC.