Using recently designed, commercially available, non-invasive instruments, we measured the thickness and elasticity of the skin of the face and ventral forearm in 170 women, and evaluated the effects of age and exposure to sunlight. Skin thickness decreased with age in ventral forearm skin, which has limited exposure to sunlight, but increased significantly in the skin of the forehead, corners of the eyes, and cheeks, which are markedly exposed to sunlight. Skin elasticity (Ur/Uf) decreased with age on both the face and forearm. The ratio of viscosity element to elasticity element (Uv/Ue) increased with age at all sites. However, delayed distension (Uv), immediate retraction (Ur), final distension (Uf), and immediate distention (Ue), as individual elements, decreased on the face and increased on the forearm with age. This tendency was more marked after correction for skin thickness. These results suggested the specificity of skin thickness and elasticity in the facial skin. Analysis using a four-element model showed no changes in the elasticity coefficient of Maxwell element on the forearm, but an increase on the face. This indicates quantitative or qualitative changes in elastic fibres in facial skin. Thus, sunlight appears to have a considerable effect on the thickness and physical properties of facial skin.
In order to further clarify the role of intercellular lipids in the water-retention properties of the stratum corneum, forearm skin of six healthy male volunteers was treated with 5% sodium dodecyl sulfate (SDS) for 1, 10, and 30 min. All treatment periods induced chapping and scaling of the stratum corneum without any inflammatory reaction, accompanied by a significant decrease in its water-retention function. Electron-microscopic analysis of SDS-treated stratum corneum revealed selective depletion of the lipids from the intercellular spaces, accompanied by marked disruption of multiple lamellae structures. Lipid analysis also showed a considerable and selective loss of intercellular lipids such as cholesterol, cholesterol ester, free fatty acid, and sphingolipids. To evaluate the recovery potential for intercellular lipids, lipids which were separated as sebaceous-rich lipids (SLs) and stratum corneum lipids (SCLs) were applied daily on SDS-treated forearm skin. Two daily applications of the SCLs which were emulsified at 10% concentration in W/O (water in oil) cream caused a significant increase in conductance, accompanied by a definite improvement in the level of scaling over no application or W/O emulsion base only, whereas SLs in the W/O emulsion base led to no significant recovery in either conductance value or scaling. When two daily topical applications of four chromatographically separated lipid fractions (cholesterol ester, free fatty acid, cholesterol, and sphingolipid) from the SCL were carried out at 1% concentration in the same system, the cholesterol ester and sphingolipid fractions were found to induce a significant increase in the conductance value over no application.(ABSTRACT TRUNCATED AT 250 WORDS)
This new analytical system provides a rapid and convenient non-invasive method to evaluate skin surface morphology in three dimensions, especially with respect to wrinkle formation. The results obtained using this system provide a deeper insight into the mechanistic relationship between wrinkles and skin elasticity.
To elucidate differential effects of ultraviolet (UV) exposure on three-dimensional networks of elastic fibers during maturation of rat skin, Sprague-Dawley rat hind limbs were irradiated with suberythemal doses of UV light (UVB, 130 mJ/cm2, or UVA, 27 J/cm2) in three different time courses of exposure: 3-9 weeks old, 9-15 weeks old, and 3-15 weeks old. Three-dimensional arrangement with special reference to linearity of elastic fibers was quantified by image analysis using a scanning electron microscope after a combination of intravascular resin injection and selective digestion technique using formic acid. Among the three irradiation groups, the group irradiated with UVB or UVA between 3 and 15 weeks old (UVB, three times per week; UVA, five times per week) elicited the most marked decrease in the linearity of elastic fibers. Despite the same irradiation period, there was a significant difference in the decreased linearity between the two irradiation groups of 3-9 and 9-15 weeks old, with the former irradiation group exhibiting greater loss of linearity than the latter irradiation group. The magnitude of the decreased linearity was greater in the UVB-exposed groups than in the UVA-exposed group. These findings indicate that the three-dimensional linearity of elastic fibers is more susceptible to disruption by UV exposures during the growth period than that after the growth period.
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