ASSESSING SKIN BARRIER INTEGRITY 183 • 5 • 4 I I I I I 0 1 2 3 4 5 Time (Weeks) Figure 6. Effect of storage temperature on the permeation of water through micro-Yucatan pig skin (skin dermatomed and dried before storage). ß 4øC, O -15øC. Each error bar represents the standard error of the mean. higher after one week and then dropped down for the remainder of the study. This time point could be a result of an experimental error. Rosenquist et al. (4) observed that the viability of pig skin remained unchanged for 30 days when stored at 4øC. Although viability is not directly related to permeability, their results show a pattern consistent with the findings of our study. Skin stored before dermatoming at 4øC for more than two weeks changed appearance and odor. Such a change was not noticed in skin stored at -15øC. This change in physical appearance was reflected in the barrier properties of the skin. This is the only storage condition where the -15øC station, though not completely satisfactory, pre- served the skin better than the 4øC station. It was observed that the permeability of pig skin to water and SA did not change when it was measured from the back and left and right hams of the pig. In contrast, abdominal rat skin was more permeable to water and benzoic acid than back skin (7). Storing the dermatomed skin at - 15 øC changed the barrier properties of the skin. This was probably due to freezing of the water in the SC. This explanation was confirmed by

184 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 0.030 0.025 '•' 0.020 o E .e. o o.o15 E x • O.OLO 0.005 0.000 I I I 1 I 0 1 2 3 4 5 Time (Weeks) Figure 7. Effect of storage temperature on the permeation of salicylic acid through micro-Yucatan pig skin (skin dermatomed and dried before storage). ß 4øC, ¸ -15øC. * Statistically significant value from the initial result. Each error bar represents the standard error of the mean. Table II Variability in Water and SA Flux Among Different Areas of the Body of the Pig Water Salicylic acid Standard error Standard error Flux of the mean Flux (x 102) of the mean (x 102) Skin area (mg/cm2/hour) (mg/cm2/hour) (mg/cm2/hour) (mg/cm2/hour) Ventral 2.45 0.584 1.08 0.135 Dorsal 2.55 0.865 1.07 0.186 Back 2.44 0.419 1.18 0.062 Left ham 2.36 0.185 1.18 0.247 Right ham 2.80 0.464 1.01 0.050 the fact that the barrier of the dried skin stored at -15 øC was less damaged than for the skin stored at - 15 øC without drying, as noted from the flux values. The results obtained confirm the findings by Hawkins and Reinfenrath (5), who showed that freezing pig skin at -80øC increased its permeability to N,N-diethyl-m-toluamide after one week.