18 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS RESULTS Table I summarizes data for permeability to water (TE•0qL) and to benzoic acid (percu- taneous absorption), and corneocyte size according to anatomic site, age, and sex. In male subjects from ages 20 to 30 cutaneous permeability to both water and benzoic acid was: forearm (ventral elbow) forearm (ventral-mid) arm (upper-outer) • abdomen • forearm (ventral-wrist) • postauricular • forehead. In the sites studied (upper-outer arm, forehead) no differences between sexes were ob- served. In relation to age, no changes in skin permeability appeared to occur before age 55. In subjects from 65 to 80 years of age (upper-outer arm), there was no change in transepi- dermal water loss. However, percutaneous absorption of benzoic acid decreased by a factor of 4 (p • 0.001). As regards corneocyte surface area, in male subjects of ages 20-30, the rank order is: forearm (ventral-elbow) -- forearm (ventral-mid) -- arm (upper-outer) = abdomen forearm (ventral-wrist) postauricular • forehead. Table I Influence of Anatomic Site, Age, and Sex on Transepidermal Water Loss (TEWL), Percutaneous Absorption of Benzoic Acid, and Corneocyte Surface Area Group no. Total penetration Transepidermal of benzoic water loss acid within Corneocyte Volunteers Age (TEWL) 4 days surface area per group Anatomic site (years) Sex (gm/m2/h) (nmol/cm 2) (p•m •) 1 2 3 4 5 6 7 8 9 10 11 8 Arm 20-30 M 4.24 a 9.15 980 (upper-outer) (0.35) b ( 1.01) (34) 8 Arm 45-55 M 5.07 10.02 994 (upper-outer) (0.23) (1.02) (56) 7 Arm 65-80 M 4.73 2.53 1141 (upper-outer) (0.45) (0.82) (63) 7 Arm 20-30 F 5.12 11.20 990 (upper-outer) (0.35) (1.20) (31) 7 Abdomen 20- 30 M 4.40 12.50 996 (0.51) (1.64) (42) 8 Postauricular 20-30 M 8.35 22.49 812 (0.41) (5.14) (23) 7 Forehead 20- 30 M 10.34 26.80 555 (0.70) (3.19) (11) 8 Forehead 20-30 F 9.39 28.99 554 (0.73) (1.81) (12) 7 Forearm 20-30 M 2.50 3.48 1004 (ventral-elbow) (0.30) (0.33) (41) 8 Forearm 20- 30 M 4.00 5.5 1 1007 (ventral-mid) (0.32) (1.70) (31) 7 Forearm 20-30 M 7.19 12.18 884 (ventral-wrist) (0.39) (1.62) (30) a Mean value. b S.D.

CORNEOCYTE SIZE AND PERMEABILITY 19 Sex (upper-outer arm, forehead) appears to have no influence on corneocyte sizeß Nor were any differences in the latter observed between the 20-30 and 45-55 age groups. In the 65-80 age group, corneocyte size increases significantly (p 0.001). Figure 2 depicts how these different parameters vary depending on anatomic site, but irrespec- tive of age and sex. The results show that although the size of corneocytes taken from sites 4, 5, 2, 1, 10, and 9 was relatively constant (980 to 1007 [•m2), there were large changes in cutaneous permeability. Between sites 9 and 4, for example, in absolute values, there was an increase of 2.6 gm ß m-2. h- • in TEWL and 7.7 nmol ß cm-2 in benzoic acid absorption. However, it appears that permeability for both water and benzoic acid becomes progressively larger with decreasing corneocyte size (sites 11, 6, 7, and 8). For example, differences of 4.3 gm ß m -2 ß h -• in TEWL and 17.8 nmol ß cm-2 in benzoic acid absorption were observed between sites 4 and 8, which had re- spective corneocyte surface areas of 990 and 555 [•m 2. An increase in permeability by a factor of about 2 appears to correspond to a decrease in corneocyte size by a factor of about 2. The relationship between corneocyte size and percutaneous absorption of benzoic acid or TEWL is depicted in Figure 3 (a,b). This figure shows that when corneocyte surface lO o •- 30 •, [ 20 ß •. '• lO E E 0 1000 75O 500 Transep •,•Penetration of ea i i i i , ! i i i i i 8 76114 5 2 I 1093 anatomic site n ø Figure 2. Evolution of transepidermal water loss, penetration of benzoic acid, and corneocyte surface area according to anatomic site, age, and sex in man. 1. Arm (upper-outer, male, 20-30 yr). 2. Arm (upper- outer, male, 45-55 yr). 3. Arm (upper-outer, male, 65-80 yr). 4. Arm (upper-outer, female, 20-30 yr). 5. Abdomen (male, 20-30 yr). 6. Postauricular (male, 20-30 yr). 7. Forehead (male, 20-30 yr). 8. Forehead (female, 20-30 yr). 9. Forearm (ventral-elbow, male, 20-30 yr). 10. Forearm (ventral-mid, male, 20-30 yr). ! 1. Forearm (ventral-wrist, male, 20-30 yr).