FUCUS EXTRACT AND SKIN THICKNESS 3 Figure 1. Typical ultrasonographic image obtained on human cheek skin. P = membrane of the ultrasound probe. G = coupling ultrasonic gel. E = epidermis. D = dermis. S = subcutaneous tissue. the echolucent subcutaneous fatty tissue. On ultrasonographic images, the thickness from the skin surface to the plane showing discontinuity of echogenicity (representing the border between the dermis and the subcutaneous tissue) was measured at ten sites, and the mean value was calculated. MEASUREMENT OF MECHANICAL PROPERTIES OF THE SKIN Mechanical properties of the skin were measured with a commercially available instru- ment (Cutometer SEM575, Courage & Khazaka, Cologne, Germany) as described pre- viously (9). Briefly, the time/strain mode was used with an 8-sec application of 200 hPa followed by a 2-sec relaxation period using a probe 2 mm in diameter (10). The parameters determined were immediate distention (Ue) measured at 0.15 sec, final distention (Uf) measured at 7.85 sec, delayed distention (Uv), and immediate retraction (Ur) (11). These parameters are a function of skin thickness, and thus cannot be simply compared between subjects. Each individual measurement of skin thickness was used to calculate the mechanical parameter values for the thickness of skin for a given individual. These normalized parameters were marked with an asterisk (Ue*, Uf*, Uv*, Ur*). STATISTICAL ANALYSIS All data were compared by the paired Student's t-test. RESULTS DIURNAL CHANGES OF HUMAN SKIN THICKNESS AND MECHANICAL PROPERTIES The skin thickness of the cheek showed slight but significant changes during the day (Table I). The Ue* and Uf* values of the skin, which are indices of the distensibility of the skin and reflect its elastic properties, did not differ significantly during the day (data not shown). The Uv* value, which reflects intradermal movements of a viscous type, and the Ur* value, which is the elastic recovery, also did not change during the day (data not shown).

4 JOURNAL OF COSMETIC SCIENCE Table I Diurnal Changes of Thickness of Human Cheek Skin Skin thickness (mm) a Morning 1.298 +/- 0.119 Evening 1.258 +/- 0.147' a Data expressed as mean +/- SD. * Significantly different between morning and evening, p 0.05. EFFECT OF THE EXTRACT OF FOCUS VESICULOSUS ON THE THICKNESS OF HUMAN CHEEK SKIN All ten volunteers completed the study without irritation or erythema. Before applica- tion, no significant differences were observed in skin thickness between the placebo- treated and the Fucm extract-treated groups measured in the morning and in the evening (Table II). However, topical application of the F•us extract gel for five weeks caused a significant decrease in skin thickness measured in the morning and in the evening compared with that of the corresponding placebo-treated controls. For example, in the Fucus extract-treated group, nine volunteers showed a decrease in skin thickness. The difference between the F•c• extract-treated group and the placebo-treated group reached about 0.1 mm, which corresponded to 7-8% of the skin thickness. The appli- cation of the placebo did not elicit any change in skin thickness measured in the morning and in the evening. Concerning a dose-dependency effect of Fucus extracts, gels including 1%, 2%, 3%, or 5% of extract showed similar results on skin thickness and elastic properties (data not shown). EFFECT OF THE EXTRACT OF FUCUS VESICULOSUS ON THE MECHANICAL PROPERTIES OF HUMAN CHEEK SKIN Before application, no significant differences were observed in Uf* and Ue* values between the placebo- and Fucm-treated groups measured in the morning and in the evening. Topical application of the F•us extract or the placebo for five weeks elicited a significant difference in the Uf* values measured in the morning and in the evening (Table III). Measured in the evening, the Uf* value increased after the application of the Fucus extract, but did not change after the placebo treatment. The Ue* values did not change significantly, although they showed a tendency to increase after five weeks of treatment (Table IV). Neither the Ur* nor the Uv* values, which are indices of the elastic recovery or viscosity parameters, showed significant differences between the Fuck extract-treated and the placebo-treated groups (data not shown). DISCUSSION In this study, we investigated the effects of topical application of a Fucus vesiculosus extract on the thickness and mechanical properties of human skin. Gniadecha et al. (12,13) reported that diurnal changes are observed in skin echogenicity in various regions of the body by using B-mode ultrasonography, which suggests that diurnal changes in skin thickness occur. At first, we examined diurnal changes in skin thickness