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.

532 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table VII Solar Simulator Vs. Westinghouse FS-20 Sunlamps Fluorescent FS-20 Sunscreen Sunlamp Tubes Solar Simulator (5/xl per cm 2) S.P.F. - S.E. S.P.F. - S.E. J 13.4 - 1.07 8.8 - 0.68 A 7.2 - 0.37 3.5 - 0.22 I 62.0 + 2.54 8.0 + 0•42 COMPARISON OF UV-LIGHT SOURCES In comparison to the solar simulator, the fluorescent sunlamps gave strikingly higher S.P.F. values for all the formulations (Table VII). The difference was most pronounced with I, where there was about an eightfold increase. DISCUSSION Recently, the Over-The-Counter (OTC) panel on topical analgesics has provided guidelines for the laboratory appraisal of sunscreens (4). These require the use of the solar simulator to determine the immediate S.P.F. of a specified UV-absorber at a dose of 2 mg]cm 2. This is intended to provide the consumer with an estimate of potency so that a choice can be made according to individual needs (skin type, geographic location, etc.) Valuable as this is, we regard the immediate S.P.F. as furnishing too limited in- formation. Millions of persons have occupations or life styles which require the regular use of sunscreens under very diverse circumstances and different environmental stresses. Our data show that proprietory formulations vary markedly in their ability to withstand sweating, water wash-off and abrasion. Moreover, since we recommend daily use for persons at risk, it is important to assess other features of safety such as extent of percutaneous absorption as well as buildup in the horny layer reservoir. Often a sunscreen performs well in one test and poorly in another. Each formulation has a "per- sonality" a complex of features which may make it either exceptional or ordinary for particular uses and users. A comprehensive evaluation cannot be made without assess- ing these various properties. To develop appropriate methodology, we had to consider a number of factors of varying importance. Since these have not been adequately dis- cussed in the literature, we shall briefly review our own thoughts and experiences. Early on, the question arose whether S.P.F. values were related in any way to skin type. Fair-skinned, blue-eyed celts are far more susceptible to sunburn than darkly pig- mented Mediterraneans. Would the S.P.F. for a given formulation be different in the two groups? We found that the mean S.P.F.'s were not different (unpublished observa- tions). The S.P.F. is a ratio and is not influenced by the susceptibility of skin to sunburn. It is advantageous, however, to use fair-complexioned subjects since their MED's are lower redness is more easily perceived and time is saved. Another question is how do laboratory S.P.F.'s compare with those obtained with sun- light? The solar simulator mimics sunlight mainly in the sunburning UV-B range but not in other regions of the spectrum. UV intensity, for example, falls sharply above 360 nm. Sayre et al. found that the S.P.F. obtained with the solar simulator was higher than with sunlight (3.6 vs. 2.4) (5). Outdoor testing was done, however, at a tempera-