Effects of skin moisturization on various aspects of touch showing differences with age and skin site

Abstract

The human body is encompassed by a thin layer of tissue, the skin, which is heterogenous and highly specialized to protect the body and encode interactions with the external world. There is a fundamental scientific drive to understand its function, coupled with the need to preserve skin as we age, which impacts on our physiological and psychological well-being. In the present study, we aimed to define differences in touch perception between age groups and with skin cream application. We investigated touch on the finger, the forearm and cheek in younger (20-28 years, n = 22) and older (65-75 years, n = 22) females. We measured skin hydration, touch detection, finger spatial discrimination, forearm tactile pleasantness together with electrodermal activity, and perceptual ratings about cream use, skin dryness, and cosmetic habits. Glabrous finger skin became drier and touch performance was impaired with age, but these aspects were preserved in hairy skin. Skin moisturization immediately increased hydration levels, but did not significantly change touch perception. We also found that touch appreciation increased with age. We conclude that reduced finger capacity may impact self-evaluation of the skin and that long-term skin care strategies should focus on hydrating the hand to preserve touch capacities.

Figure 1

Self-perceived skin types and habitual moisturizer use for the younger and older groups. For the younger (n = 22) and older (n = 22) groups, their (a) self-reported face skin type is shown at the top left and body skin type on the bottom left. (b) Frequency of self-reported moisturizer use for facial day creams (top right), facial night creams (middle right), and body creams (bottom right) for the same participants. The frequencies of each measure are shown. Mann–Whitney tests where significant, are denoted on the title of each sub-figure as *p < 0.05, **p < 0.01.

Figure 2

Skin water content between skin sites, over age groups, and with cream application. The percentage of skin water content is shown for each of the three skin sites tested (from left to right: finger, arm, cheek), where for each site, the water content before and after cream application is shown, for individuals in the younger group (n = 22, filled lighter gray circles, with a continuous line showing the means before-after cream application) and older group (n = 21, filled darker gray triangles, with a dotted line showing the means before-after cream application). The data show the mean values averaged over both cream tests and upper and lower 95% confidence intervals of the mean are shown at each mean point. Before cream application, water content was highest at the finger for both groups, but the young participants had significantly more water in the finger skin, as compared to the older participants at the finger. Cream application significantly increased skin water content over each skin site and for each group, apart from the young group on the finger and the older group on the arm.

Figure 3

Tactile detection sensitivity over age groups at different skin sites. The monofilament tactile force detection (in mN) was measured in 43 participants (young group = 22, shown as filled lighter gray circles, with a continuous line showing the means between skin sites; older group = 21, shown as filled darker gray triangles, with a dotted line showing the means between skin sites) on glabrous finger skin and on hairy arm and cheek skin. The data show the mean values averaged over before and after cream application and for both creams and upper and lower 95% confidence intervals of the mean are shown at each mean point. There were significant main effects of age group and skin site, and an interaction between these, where there was only a significant difference between force detection threshold between the younger and older group at the finger.

Figure 4

Finger tactile discrimination capacity in the younger and older groups before and after cream application. Participants discriminated between striated plates that had different spatial periods. A significant main effect of age group was found, where the younger group (n = 22, left side of graph) had better discrimination than the older group (n = 20, right side of graph), but no difference was found before (lighter gray circles) or after (darker gray circles) cream application. The black lines show the means for each age group, for before and after cream application and upper and lower 95% confidence intervals of the mean are shown.

Figure 5

Pleasantness ratings over different velocities for the younger and older groups and electrodermal activity over the stroking conditions. Participants’ arms were stroked at different velocities before and after cream application. (a) Pleasantness ratings (range − 10 unpleasant to + 10 pleasant) for the younger (n = 22, filled gray circles, with the means connected as a continuous line) and older (n = 19, filled black triangles, with the means connected as a dotted line) groups over each stroking velocity (presented as a categorical log10 scale), showing a significant effect of age group and velocity. The lines showing the means also show the upper and lower 95% confidence intervals of the mean. During the stroking, electrodermal activity (EDA) was measured and significant differences were found for (b) stroking velocity, (c) age group, and (d) before and after cream application. As the data were highly skewed, medians are shown with 95% confidence intervals of the median, and each sub-figure y-axis is presented on a log2 scale, for better visualization of the data.

Figure 6

Perceptual ratings of cream characteristics during use. Median ratings (with 95% confidence intervals of the median) of individual participant datapoints are shown for each age group (younger n = 22, older n = 21 participants) for six perceptual measures of cream use. For (a) to (f), ratings are shown for differences between the age groups on: (a) how much the participants liked using the cream, (b) the smoothness of the cream, (c) the freshness of the cream, (d) the greasiness of the cream, (e) the heaviness of the cream, (f) the stickiness of the cream. For (g) to (i), ratings are shown for differences between ratings over skin sites on: (g) the greasiness of the cream, (h) the heaviness of the cream, (i) the stickiness of the cream. Asterisks for significant differences on Kruskal–Wallis tests are denoted as **p < 0.01, **p < 0.001, where for (g) face ratings were significantly lower than for the arm, (h) arm ratings were significantly lower than on the cheek and face, (i) arm ratings were significantly higher than on the cheek and face. Note that confidence intervals that do not appear above and/or below mean that the interval is at the median.

Figure 7

Significant correlations between selected measures of skin water content, tactile detection, and self-reported face skin classification. (a) Correlation of skin water content at the forearm and cheek (Pearson p < 0.001). (b) Relationship between finger water content and tactile detection threshold (Pearson p < 0.001). (c) Correlation between self-reported face skin dryness classification with finger water content (Spearman p = 0.005. Each dot represents a participant (n = 43), with the solid line showing the correlation and the dotted lines the upper and lower 95% confidence intervals.