Antigen used Quantifi cation of responses via suppression of induction IPF calculation via suppression of induction studies Reference Kit containing seven antigens (tetanus toxoid, diphtheria toxoid, Streptococcus, tuberculin, Candida albicans , Trichophyton mentagrophytesand , Proteus mirabilis) Summed the mean diameter of each positive reaction to each recall antigen to obtain a total score for each volunteer. Reaction borders were defi ned by redness and induration Could not calculate IPF, but determined whether the IPF was equal to or not to the SPF by comparing each pre- and post-SSR DTH score with a paired t Then, comparisons between sunscreen and non-sunscreen groups were compared by analysis of variance and Tukey’s tests (82) Nickel Quantifi ed the CHS response to nickel by determining an erythema index (EI) by refl ectance spectroscopy. After subtraction of the background (absence of nickel patch), the EI of the exposed sites (with or without sunscreen) was compared with the EI of the appropriate unirradiated nickel-patched sites. The results are expressed as ΔEI = EI (unirradiated control) − EI (test site) Compared the EI induced by the nickel CHS response (minus the skin background color) at non-SSR exposed sites with the EI at test sites. Statistical signifi cance was assessed by the paired t to determine the amount of SSR to achieve immunosuppression. The SSR doses that reduced the mean EI of the unirradiated skin by 20% were calculated, for both protected and unprotected sites, and were defi ned as minimal immunosuppressive doses (MISD) IPF = MISD of protected skin/MISD of unprotected skin. A calculation used pooled rather than individual volunteer data (83) Table III Continued UV PROTECTION AND EVALUATION OF EFFICACY OF SUNSCREENS 335

JOURNAL OF COSMETIC SCIENCE 336 specifi c interval after irradiation, and the minimal persistent pigment darkening dose (MPD) is determined as the lowest UV dose that produces substantial tanning with clearly defi ned borders. The UVA-PF is calculated as the ratio of the MPD of sunscreen protected to unprotected skin, as described by Chardon et al. (84). SUNSCREEN ABSORBANCE DETERMINATION An in vitro method proposed by Diffey et al., 1994, is based on the shape of the absorption spectrum of a sunscreen product, which is obtained using spectrophotometry The spec- tral absorbance profi les of different sunscreens is obtained using a UV-1000 SPF analyzer with sunscreen applied at 2 mg/cm2 on to a quartz plate substrate profi led with the to- pography of skin samples (85). Two different methods of rating UVA protection can be calculated from the absorbance spectra. The Diffey critical wavelength is that wavelength below and including which 90% of the total UV is absorbed by a sunscreen from 290 nm to 400 nm (85). Higher critical wavelengths, therefore, indicate better UVA protection. The critical wavelength determination does not promote the fake belief of UVB and UVA as split entities, but rather as part of the uninterrupted electromagnetic range. The Boots UVA ratio is the ratio of the total absorption by a sunscreen in the UVA region compared with that in the UVB region. A signifi cant positive correlation was observed between IPF and the Diffey critical wave- length. Similarly, there was also a signifi cant positive correlation between IPF and the Boots UVA ratio. Both these parameters measure the breadth of a sunscreen’s protection and thus show that the spectral broadness of a sunscreen is an important factor for im- munoprotective capability (79). A complete description of a product’s photoprotective distinctiveness fallout when the critical wavelength is used in concurrence with SPF. However, this in vitro spectropho- tometry measurement lacks the signifi cance to a scientifi c/biological endpoint easily grasped by the public. IPF possibly has a better correlation with the UVA protectiveness of sunscreen than with the SPF. Furthermore, a more elementary method for measuring sunscreen’s immunoprotective capacity is required. PHOTOSTABILITY OF SUNSCREENS The photostability of active ingredients of a sunscreen product is also of foremost appre- hension. As discussed before, sunscreen ingredients absorb or refl ect and scatter radiation throughout the episode they are anticipated to offer a shield for, and consequently they ought to be stable photochemically. However, several chemical fi lters show signs of some photoreactivity (negligible or noteworthy) and lead to formation of photoproduct(s) that might still act as a fi lter (e.g., photoisomerization reaction) or presence of such products may lead to diverse protection spectra for different sunscreens and consequently infl uence their safeguard. Photostability depends on the main fi lter, presence of other fi lters, and on solvent or vehicle of the sunscreen product. In order to achieve an effective formulation, it is important to fi nd photostable excipients.