Artificial intelligence model substantially improves stratum corneum moisture content prediction from visible-light skin images and skin feature factors.

BACKGROUND: Appropriate skin treatment and care warrants an accurate prediction of skin moisture. However, current diagnostic tools are costly and time-consuming. Stratum corneum moisture content has been measured with moisture content meters or from a near-infrared image. OBJECTIVE: Here, we establish an artificial intelligence (AI) alternative for conventional skin moisture content measurements. METHODS: Skin feature factors positively or negatively correlated with the skin moisture content were created and selected by using the PolynomialFeatures(3) of scikit-learn. Then, an integrated AI model using, as inputs, a visible-light skin image and the skin feature factors were trained with 914 skin images, the corresponding skin feature factors, and the corresponding skin moisture contents. RESULTS: A regression-type AI model using only a visible-light skin-containing image was insufficiently implemented. To improve the accuracy of the prediction of skin moisture content, we searched for new features through feature engineering ("creation of new factors") correlated with the moisture content from various combinations of the existing skin features, and have found that factors created by combining the brown spot count, the pore count, and/or the visually assessed skin roughness give significant correlation coefficients. Then, an integrated AI deep-learning model using a visible-light skin image and these factors resulted in significantly improved skin moisture content prediction. CONCLUSION: Skin moisture content interacts with the brown spot count, the pore count, and/or the visually assessed skin roughness so that better inference of stratum corneum moisture content can be provided using a common visible-light skin photo image and skin feature factors.

Molecular Reorganization during the Formation of the Human Skin Barrier Studied In Situ.

In vertebrates, skin upholds homeostasis by preventing body water loss. The skin's permeability barrier is located intercellularly in the stratum corneum and consists of stacked lipid lamellae composed of ceramides, cholesterol, and free fatty acids. We have combined cryo-electron microscopy with molecular dynamics modeling and electron microscopy simulation in our analysis of the lamellae's formation, a maturation process beginning in stratum granulosum and ending in stratum corneum. Previously, we have revealed the lipid lamellae's initial- and end-stage molecular organizations. In this study, we reveal two cryo-electron microscopy patterns representing intermediate stages in the lamellae's maturation process: a single-band pattern with 2.0‒2.5 nm periodicity and a two-band pattern with 5.5‒6.0 nm periodicity, which may be derived from lamellar lipid structures with 4.0‒5.0 nm and 5.5‒6.0 nm periodicity, respectively. On the basis of the analysis of the data now available on the four maturation stages identified, we can present a tentative molecular model for the complete skin barrier formation process.

Stratum corneum drying drives vertical compression and lipid organization and improves barrier function in vitro.

The stratum corneum dehydrates after exogenous hydration due to skincare or bathing. In this study, sheets of stratum corneum were isolated from reconstructed human epidermis and the barrier function and structure of these sheets were assessed during drying with the aim of improving our understanding of skincare. Water diffusion through the sheets of stratum corneum decreased with drying, accompanied by decreased thickness and increased visible light transmission through the sheets. Electron paramagnetic resonance revealed that the order parameter values of stratum corneum lipids increased with drying. X-ray diffraction analysis revealed increases in the diffraction intensity of lamellar structures, with an 11-12 nm periodicity and spacing of 0.42 nm for lattice structures with drying. These results suggest that the drying process improves the barrier function of the stratum corneum by organizing the intercellular lipids in a vertically compressed arrangement.

The human skin barrier is organized as stacked bilayers of fully extended ceramides with cholesterol molecules associated with the ceramide sphingoid moiety.

The skin barrier is fundamental to terrestrial life and its evolution; it upholds homeostasis and protects against the environment. Skin barrier capacity is controlled by lipids that fill the extracellular space of the skin's surface layer--the stratum corneum. Here we report on the determination of the molecular organization of the skin's lipid matrix in situ, in its near-native state, using a methodological approach combining very high magnification cryo-electron microscopy (EM) of vitreous skin section defocus series, molecular modeling, and EM simulation. The lipids are organized in an arrangement not previously described in a biological system-stacked bilayers of fully extended ceramides (CERs) with cholesterol molecules associated with the CER sphingoid moiety. This arrangement rationalizes the skin's low permeability toward water and toward hydrophilic and lipophilic substances, as well as the skin barrier's robustness toward hydration and dehydration, environmental temperature and pressure changes, stretching, compression, bending, and shearing.

Increased carbonyl protein level in the stratum corneum of inflammatory skin disorders: A non-invasive approach.

The stratum corneum (SC) is the interface of body and environment, and is continuously exposed to oxidative stress, resulting in carbonyl modification of proteins. We have developed a simple and non-invasive method to assess carbonyl protein (CP) level in the SC, applied it to various kinds of skin, and revealed a link between the stratum corneum carbonylated protein (SCCP) level and water content in the SC. The purpose of the present study is to examine the SCCP level in inflammatory skin disorders associated with xerosis. Psoriasis vulgaris (PV) and atopic dermatitis (AD) are typical inflammatory skin disorders, of which the stratum corneum shows markedly low water content. SC samples were non-invasively collected from the lesional and non-lesional areas of PV and AD by adhesive tape stripping, and their carbonyl groups were determined by reaction with fluorescein-5-thiosemicarbazide. The average fluorescence intensity of the SC was calculated as SCCP level. Higher SCCP level was observed in the lesional area of PV as compared with non-lesional area or healthy control. Lesional area of AD also exhibited higher SCCP level than corresponding non-lesional area, of which SCCP level was slightly higher than the healthy control. These data suggest the involvement of oxidative modification of the SC protein, at least in part, in generation of xerotic skin in inflammatory skin disorders as well as dry skin in healthy subjects.