530 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table IV Cumulative Effects (Immersion) Sunscreen Average Erythema a +- S.E. Range H 2.8 +- 0.16 2-3 D 2.3 +- 0.42 1-3 J 2.2 --- 0.30 1-3 Zinc Oxide Ointment 1.8 + 0.16 1-2 F 1.3 +- 0.36 0-3 L 1.0 + 0.37 0-3 M 0.8 +- 0.30 0-2 I 0.8 + 0.23 0-2 aErythema 24 hr after three MED's. CUMULATIVE EFFECT Marked differences were observed among the test materials (Table IV). Those contain- ing PABA and its esters showed high residual protection. Others, H in particular, demonstrated virtually no buildup. SCOTCH-TAPE STRIPPING Although removal of the uppermost superficial layers of the stratum corneum by strip- ping is a variable technique, there were striking differences. Protection from J, H and F was practically abolished (Table V). By contrast, I and L were highly effective. DOSE-RESPONSE STUDIES Protection was clearly dose-dependent (Figure). The $.P.F.'s increased with larger amounts of sunscreen, though not in any fixed way. With H increasing the dose from 2.5 to 5.0/•l/cm 2 practically doubled the S.P.F. At higher dosages (5.0 to 10.0/•l/cmZ), the increases in the S.P.F. for A and I were much less impressive than for H and zinc oxide ointment. PROTECTION AGAINST UV-A The test agents differed markedly. A PABA sunscreen (I) provided virtually no protec- tion, while the benzophenone-containing agents were moderately effective, as were the physical blockers (Table VI). E, which contains 5 % titanium dioxide, was more ef- fective than zinc oxide ointment. Table V Cumulative Effects (Scotch-tape stripping) Sunscreen Mean Erythema Score + S.E. Range F 2.63 + 0.18 2-3 J 2.62 +- 0.18 2-3 H 2.50 + 0.19 2-3 I 0.63 -+ 0.26 0-2 L 0.50 --- 0.27 0-2

EFFICACY OF SUNSCREENS 531 x 15 10 A Zinc Oxide Ointment o 2.5 5.0 Dose (•zl/c 2 ) Figure 1. The influence of topical dose of sunscreen on the S.P.F. 10.0 Table VI Protection Against UV-A Induced Phototoxicity to Fluoranthrene a (n = I0) Sunscreen Mean P.F. + S.E. Range I 1.2 _+ 0.12 1.0-1.5 RVP 1.7 -+ 0.17 1.0-2.0 H 2.0 + 0.22 1.5-3.0 J 3.0 -+ 0.62 1.7-5.0 Zinc Oxide Ointment 3.1 -+ 0.55 2.0-5.0 E 4.4 -+ 0.73 3.0-7.0 G 4.6 -+ 0.83 2.5-8.0 din order of increasing efficacy. P.F. values below 3.0 are indicative of poor protection.