Skin indentation firmness and tissue dielectric constant assessed in face, neck, and arm skin of young healthy women.

PURPOSE: Our goal was to test the hypothesis that skin firmness correlates with skin hydration. METHODS: Dermal water was assessed by tissue dielectric constant (TDC) at 0.5 mm (TDC0.5 ) and 2.5 mm (TDC2.5 ) depths on four face sites and two arm sites of 35 women (25.0 ± 1.6 years). Firmness was determined by force (mN) to indent skin to 0.3 mm (F0.3 ) and 1.3 mm (F1.3 ). RESULTS: F0.3 was similar among face sites (avg = 16.2 ± 7.2 mN) but F1.3 varied (avg = 32.5 ± 4.1 mN). TDC2.5 was similar among face sites (avg = 37.7 ± 4.2) but TDC0.5 varied (avg = 36.2 ± 4.8). F1.3 of arm sites was similar (avg = 60.2 ± 18.6 mN) and both greater than F1.3 of neck (28.3 ± 7.1 mN) and face. Regression analysis showed a near-zero correlation between forces and TDC at all sites. CONCLUSION: The near-zero correlation may be due to low skin interstitial hydraulic resistance to mobile water movement in healthy young skin. If true, then conditions in which dermal hydraulic conductance is reduced as in lymphedematous, diabetic, or aged skin are more likely show the hypothesized relationship. Our findings provide normalized reference values and suggest that such persons are an important population to study to test for a possible skin water-indentation force relationship and its utilization for early diagnosis.

Stratum corneum compliance enhances tactile sensitivity through increasing skin deformation: A study protocol for a randomized controlled trial.

BACKGROUND: Tactile sensation plays a crucial role in object manipulation, communication, and even emotional well-being. It has been reported that the deformability of skin (also described as skin compliance) that shows a large mechanical response to stimuli is associated with high tactile sensitivity. However, although the compliance of the stratum corneum, the outermost layer of skin, can change daily due to skin care and environmental factors, few studies have quantified the effect of the stratum corneum on tactile sensation. AIMS: We investigated the changes in tactile sensitivity resulting from skin hydration and identified corresponding alterations in the compliance of the stratum corneum. METHODS: A randomized controlled trial was conducted. Participants were randomly assigned to an intervention group (n = 20) that had a moisturizing cream applied to their cheeks or a control group (n = 19) that had Milli-Q water applied to their cheeks. Tactile discrimination performance was assessed using psychophysical techniques before and after application. The water content, mechanical response characteristics, and penetration of PEG/PPG-17/4 dimethyl ether from the cream in the stratum corneum were evaluated to identify hydration effects. Skin deformations occurring during tactile sensation were measured concurrently using a suction device employed for tactile stimulation. RESULTS: Tactile sensitivity was increased in participants who had cream applied to the skin surface, while no significant change was observed in participants who received Milli-Q water. The improved discrimination of tactile stimulus intensity was directly related to the magnitude of skin displacement. The higher water content of the stratum corneum due to cream application decreased the dynamic modulus of elasticity of the stratum corneum and increased the skin's extensibility in response to tactile stimuli. CONCLUSIONS: Hydrating the stratum corneum significantly enhances tactile sensitivity and is accompanied by an increase in skin extensibility, a factor in tactile intensity perception. The compliance of the thin stratum corneum layer plays a crucial role in tactile experiences that involve skin stretching.