EXPERIMENTAL STUDIES ON PERCUTANEOUS ABSORPTION 243 1.8 1.5 2.55 EFFECT OF DIMETHYLFORMAMIDE ON TRANS-EPIDERMAL WATER LOSS. FLEXOR ASPECT OF MID-FOREARM NORMAL ANHIDROTIC SKIN THREE SUBJECTS 2 4 6 8 12 16 TIME AFTER EXPOSURE (HOURS) Figure 20 Effect of dimethylformamide on transepidermal water loss. cutaneous penetration [for instance, of steroids (3)] might be partly attributable to a direct effect on the corneous barrier and not simply to their properties as steroid solvents. The experiments were performed on the normal flexor forearm. After initial TEWL measurements had been made (on anhidrotic skin) the cream or aqueous solution (the latter on saturated lint) was applied under poly- thene occlusion and left in situ for 16 h. On removal of the occlusive dressing, the treated area was left uncovered for 2« h and then exposed to a stream of dry nitrogen for a further 30 min to ensure thorough desorption of the stratum corneum after the period of occlusion. TEWL was again measured. The results are summarised in Fig. $. Outward water diffusion was increased in all five subjects by THFA and doubled in three of these. The DMA cream which contained 25% DMA and 10% water (and which would

244 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 1.5 1.0 0.5 EFFECT OF DIMETHYLACETAMIDE ON TRANS-EPIDERMAL WATER FLEXOR ASPECT OF MID-FOREARM NORMAL ANHIDROTIC SKIN THREE SUBJECTS A 8 12 16 20 TIME AFTER EXPOSURE (HOUI•) Figure Effect of dimethylacetamide on transepidermal water loss. RFFECT OF DMSO, DMF AND DMA ON WATER LOSS EXPRESSED AS P•RCENTAOR INCREASES OVER PRE-TREATMENT READINGS. DMF Figure 8 12 16 20 TIME AFTER EXPOSURE HOURS Effect on DMSO, DMF and DMA on water loss expressed as percentage increases over pre-treatment readings.