66 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 1.0 ..• o.$ E 0 :• o6 E O4 0.2 o .(6} 0.0 (3)(3). (7) ß ß (5) :(7} .(7) :{7) x :(71 x :(s) i(s) I I I I I i I 0.2 0.4 0 6 0.$ 1.0 RELATIVE HUMIDITY ( H20) Figure 1. Effect m c humidity on SC hydration: (o) cantharidin or trypsin samples (x) callus sample. Since most of data points were superimposed on each other, number experimental points at each RIt is indicated by number in parentheses Table I Effect of Harvest Method on SC Hydration Hydrated b Sample a Dry Weight (rag) (mg H./mg SC) Cantharidin (23) 0.48 q- 0.07 0.77 _ 0.14 Trypsin (9) 0.50 _--*- 0.07 0.84 _--*- 0.17 Sunburn exfoliated (11) 0.38 q- 0.17 • 1.08 q- 0.08 c "liarvest method (number of samples). •'Eight mm punch hydrated for 48 hours at 97 per cent RH, 30 ø C, mean q- "Statistically different from cantharidin and trypsin harvested samples at the 99 per cent level of significance (a • 0.01).

WATER AND THE HORNY LAYER Sample b Table II Effect of Heat on SC Hydration Hydration (mg H20/mg SC) • Control After 10 min. at 60øC 67 Trypsin -- 10 0.57 0.62 -- 11 O.63 0.57 Cantharidin -- 10 0.68 0.71 -- 11 0.88 0.75 Sunburn exfoliate - 10 1.03 1.14 - 11 1.12 1.16 •'Hydration from dry weight to hydrated weight at 97 per cent BH and 30øC for 48 hours. "Samples harvested by the techniques indicated numbers 10 and 11 designate 2 different 8 mm punches from the same specimen. Table III Effect of Aqueous Exposure with Different Harvest Methods Dry Weight following Aqueous Exposure (hour) ' Harvest Method Control: 0 1 hour 3 hours 10 hours 24 hours Trypsin 0.522 0.518 0.537 0.507 0.497 Cantharidin 0.469 0.457 0.480 0.457 0.463 Sunburn exfoliate 0.362 0.349 0.312 0.259 0.337 Hydration following Aqueous Exposure (hour) b Trypsin 0.91 0.92 0.85 0.72 0.51 Cantharidin 0.90 0.86 0.89 0.76 0.85 Sunburn exfoliate 1.22 1.07 0.97 0.63 0.67 •Dry weight (in milligrams) of 1 of 5, 8 mm punches from the same specimen, following water exposure by immersion in distilled water for the time indicated. •'Hydration at 97 per cent RH, 30øC for 48 hours (rag H20/mg SC). Alternately, hydration of the SC has been treated as a pseudo-first order process, since H,20 is present in excess (8,9). The vater veight gain is ex- pressed dW/dt = K• u (Wm•.,- W) (2) Rearranging eq. 2 gives dW = r• • dt (3) (Wmax -- •V)