396 JOURNAL OF COSMETIC SCIENCE A 2.5 1.5 0.5 0 B 2.5 a 1.5 o•,• 0.5 0 c 0.5 o 1.5' 1.0 0ø, o y= -0.00099x+1.56 r= -0.105 20 40 60 80 100 Age(years) y= 0.00120x+1.49 r=- 0.105 2O 4O 6O 8O 100 Age(years) ß ' ß •" ß ß ß y= 0.00672x+1.30 r= 0.508 20 40 60 80 100 Age(years) y= -0.00118x+l.ll r=- -0.161 20 40 60 80 100 Age(years) Figure 4. Skin thickness at several sites as a function of age when measured in the afternoon (n = 90). A: forehead. B: corners of the eye. C: cheeks. D: forearms.

DIURNAL VARIATION AND SKIN THICKNESS 397 Concerning the effects of the time of measurement on age-related changes in skin thickness (diurnal variations), such changes were observed in the forehead, the corners of the eye, and the forearms in the morning but not in the afternoon. However, the cheeks showed an age-related increase in skin thickness in both the morning and the afternoon. Therefore, cheek skin might differ from other areas in structure and might be less affected by derreal fluid content than other facial sites. In addition, the effects of diurnal variations on age-related changes in skin thickness observed in this study may be due to an age-related increase in the degree of transfer of dermal fluid. Thus, diurnal variations are an important factor, especially when age-related changes in the skin thickness of the face are evaluated. The skin thickness of the face appears to be more markedly affected than other areas by dermal fluid, and the measurement obtained in the morning may reflect age-related changes more markedly. In the forearm, skin thickness showed an age-related decrease in the morning but no age-related change in the afternoon. In females with a mean age of 30 years who took part in this study, diurnal variations in skin thickness and the echogenicity of ultraso- nographic images were similar between the forearm and the face, showing a decrease in skin thickness and an increase in echogenicity in the afternoon (12). Skin elasticity in the forearm increased in the afternoon, but the increase was not so marked as that observed in the face (12). Other investigators have reported an increase in echogenicity in the forearm 12 hours after rising in the morning, both in young and in aged groups (14). It seems likely that in forearm skin derreal fluid might have slighter effects on age- related changes. In conclusion, when measuring skin thickness, an appropriate time for taking measurements should be selected with consideration of diurnal movements of dermal fluid. REFERENCES (1) H. Alexander and D. I. Miller, Determining skin thickness with pulsed ultrasound,J. Invest. Dermatol., 72, 17-19 (1979). (2) J. D. Rigal, C. Escoffier, B. Querleux, P. Agache, andJ. L. Leveque, Assessment of aging of the human skin by in vivo ultrasonic imaging. J. Invest. Dermatol., 93, 621-625 (1989). (3) S. Seidenari, A. Pagnori, A.D. Nardo, and A. Giannetti, Echographic evaluation with image analysis of normal skin: Variation according to age and sex, Skin Pharmacol., 7, 201-209 (1994). (4) B. D. Fornage andJ. L. Deshayes, Ultrasound of normal skin,J. Clin. Ultrasound, 14, 619-622 (1986). (5) L. O. Olsen and J. Setup, High-frequency ultrasound scan for non-invasive cross-sectional imaging of psoriasis, Acta Derm. VenereoL, 73, 185-187 (1993). (6) M. C. Branchet, S. Boisnic, C. Frances, and A.M. Robert, Skin thickness changes in normal aging skin, Gerontology, 36, 28-35 (1990). (7) C. Y. Tan, B. Starham, R. Marks, and P. A. Payne, Skin thickness measurement by pulsed ultrasound: Its reproducibility, validation and variability, Br. J. Dermatol., 106, 657-667 (1982). (8) S. Shuster, M. M. Black, and E. McVitie, The influence of age and sex on skin thickness, skin collagen and density, Br. J. Dermatol., 93, 639-643 (1975). (9) Y. Takema, Y. Yorimoto, M. Kawai, and G. Imokawa, Age-related changes in the elastic properties and thickness of human facial skin, Br. J. Dermatol., 131,641-648 (1994). (10) M. Gniadecka and G. B. E. Jemec, Quantitative evaluation of chronological aging and photoaging in vivo: Studies on skin echogenicity and thickness, Br. J. Dermatol., 139, 815-821 (1998). (11) G. Pellacani and S. Seidenari, Variation in facial skin thickness and echogenicity with site and age, Acta Derre. Venereol., 79, 366-369 (1999). (12) K. Tsukahara, Y. Takema, S. Moriwaki, T. Fujimura, and G. Imokawa, Derreal fluid translocation is an important determinant of the diurnal variation in human skin thickness, Br. J. Dermatol. (in press). (13) K. Tsukahara, Y. Takema, S. Moriwaki, T. Fujimura, T. Kitahara, and G. Imokawa, Age-related alterations of echogenicity in Japanese skin, Dermatology, 200, 303-307 (2000). (14) M. Gniadecka, J. Serup, and J. Sondergaard, Age-related diurnal changes of dermal oedema: Evaluation by high-frequency ultrasound, Br. J. DermatoL, 131, 849-855 (1994).