58 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table II Experiment II: Irritation of Two Retinoids, Two Concentrations Each, and Their Vehicles on Normal Forearm Skin (N = 5) After Application Once Daily 5/7 d for 28 d Irritation None Slight Weak Moderate Strong Isotretinoin 1.5% Isotretinoin 0.5% Acetone Motretinid 0.5% Motretinid 0.25% Gel base 2 3 4 1 5 1 2 2 1 1 3 3 2 pendent increase of up to 217% (0.5% gel), 155% (0.25% gel), and 93% following the gel base (first week of treatment) (Figure 5). The mean surface area was reduced dose-dependent, ranging between 4% and 16%. The highest decrease was caused by 1.5 % isotretinoin (Figure 6). DISCUSSION The exfoliative cytology of the human stratum corneum is one way to describe the effects of topically applied compounds or systemically given drugs. Over the past years +250 +20 O +150 +100- +5O CORNEOCYTE COUNTS -50- I TREATMENT I 6 • :• • • WEEKS •) • O--OI SOTRETINOIN 1.5• v--vl SOTRETIN OIN O.5Y. ¸--¸ACETONE Figure 4. Experiment II: Changes in corneocyte counts following treatment with isotretinoin 1.5% and 0.5 % and acetone.

•c +250 +20 0 +150- +100 +50- CORNEOCYTE COUNTS 59 -50- [ TREATMENT ] , '_-- 6 • • • •i WEEKS ß --ß MOTRETINID • MOTRETINID 0.257ø /•--/• GEL BASE Figure 5. Experiment II: Changes in corneocyte counts following treatment with motretinid 0.5% and 0.25% and the gel base. -lO AREA of CORNEOCYTES C)- •C) t--t I SOTRETINOIN 1.5Y. L TREATMENT V--V I SOTRETINOIN O.5•. I OmOA CETON E Figure 6. Experiment II: Changes in corneocyte areas following treatment with isotretinoin 1.5% and O. 5 % and acetone.