Fine wrinkle formation: etiology and prevention.

Wrinkles are thought to be caused primarily by a decrease in skin elasticity. While wrinkles due to changes in the dermis have been shown to be associated with alterations in elastic and collagen fibers in dermal tissue,(1-4) the mechanism of wrinkle formation due to changes in the epidermis is still unclear. Speculations about the role of physiological changes, such as dryness and barrier function(5) in the stratum corneum formed in the final phase of epidermal keratinization(6) have not been definitively confirmed. In this study, we quantified fine wrinkles, which reflect changes in the surface layer, and analyzed their association with stratum corneum function.

State and Awareness of Wrinkles

The cheeks and eye corners were selected as sites where wrinkles were evaluated. The degree of wrinkling was scored according to wrinkle depth and length, from 1 (smooth texture in a given direction) to 9 (clearly identifiable wrinkles) (Figure 1). Fine wrinkles (that seem to be closely associated with stratum corneum) were evaluated, and the scores for fine wrinkles were determined by the female subjects. While subjects generally recognized scores of 4 to 5 as fine wrinkles regardless of their age, there are marked individual differences. In females whose mean score was 4.5 to 4.6, the mean score identified as fine wrinkles was slightly lower (4.5) by those who thought they did have fine wrinkles than by those who did not (4.7). Analyzing the perception of subjects who rated themselves as having fine wrinkles, the mean score attributed to fine wrinkles was again lower (4.3) by those concerned about fine wrinkles, than by those who were not concerned (4.75) (Figure 2).

Quantification by Image Analysis

For quantitative analysis of fine wrinkles, replicas of facial sites were obtained (Figure 3a). A technique was developed to process images obtained by illuminating the replicas at an angle of 30 degrees to differentiate fine from marked wrinkles. Replicas of eye corners were obtained from each of the nine wrinkle score groups, and their shadow patterns analyzed by the following technique:

1. Marked wrinkles: After binarization alone, only marked wrinkles appeared (Figure 3b).

2. Fine wrinkles 1: After the slope of the luminance of the image was maximized by edge processing (i. e., linear differential filtering), binarization of the image revealed fine wrinkles, including fine skin texture (Figure 3e).

3. Fine wrinkles 2: Smoothing filtering (i.e., averaging the luminance in 3x3 picture element areas)…