UV PROTECTION AND EVALUATION OF EFFICACY OF SUNSCREENS 331 resolved as many antioxidants degrade upon UV exposure, for example, ascorbic acid (63,64) and vitamin E (65). Delivery of topical AOs has the potential to supply additional benefi ts to oral therapy, still, there are certain challenges associated. EVALUATION OF EFFICACY OF SUNSCREENS The degree and time taken for sunburn is generally affected by skin type. According to Food and Drug Administration (FDA), skin can be classifi ed on a scale of 1 to 6. Lower number skin types (1 and 2) represent fair skin that burns rapidly and more severely, whereas higher number skin types (5 and 6), represent darker skin that does not burn easily. On the other hand, UV index is also very important as it predicts the level of UV radiation in the atmosphere. It runs from 1 to 11 and its higher value expresses a larger degree of UV irradiation and hence requires extra caution and protection (66,67). SPF is calculated according to specifi cations approved by the European Commission or by USFDA. The solar simulating radiation (SSR) spectra is signifi cant in SPF determination. The amount of UV radiation reaching a given location on earth varies according to season as well as according to geographic location e.g. intensity of UV radiation is highest at equator and high altitude and decreases with increase in latitude. Furthermore, the outcome of this ex- treme spectrum coupled with the high UVB dependence for erythema is that SPF is mainly a measure of UVB protection with no quantitative information on UVA. Research data in bulk are available to confi rm the use of sunscreens for sun protection along with immunosuppression but on the same point it specifi es that the intensity of immune protection offered by sunscreen cannot essentially be called from its SPF. The possible jus- tifi cation regarding this is the difference in action spectra for erythema and immunosup- pression with UVA. Hence, it is being recommended that more direct human studies should be done to corroborate this. In summation, all these effects are UVR dose dependent (68). SUN PROTECTION FACTOR The standard method of assessing sunscreen protection is based on erythema and is ex- pressed as SPF. According to the FDA labeling requirement for sunscreens, mentioning of SPF is mandatory. The SPF reveals the relative amount of sunburn protection that a sunscreen can provide to the user (tested on skin types 1, 2, and 3) when used in the ap- proved manner. SPF is the sole criterion of the protection afforded by sunscreens on which manufacturers agree to characterize sunscreen labeling. SPF is a ratio calculated from a very simple formula, that is SPF = MED with sunscreen/MED without sunscreen where, MED (minimal erythema dose) is the amount of UV radiation that will produce minimal erythema on skin within few hours following exposure. SPF 15 is the lowest grade being incorporated in sunscreens. It is observed that the claimed sun protection is often not achieved as sunscreens are applied at lower densities than that rec- ommended by regulatory bodies (2 mg/cm2). Furthermore, users normally misinterpret the extent of sun protection provided by different grades of SPFs. For example, users feel that SPF

JOURNAL OF COSMETIC SCIENCE 332 30 would provide double sun protection than that provided by SPF 15. However, it is worth mentioning that SPF 15 transmits 6.66% of UVB radiation, whereas SPF 30 transmits 3.33% protection. Although the SPF ratings found on sunscreen packages apply mainly to UVB rays, many sunscreen manufacturers include ingredients that protect the skin from some UVA rays as well. These “broad-spectrum” sunscreens are highly recommended. IMMUNOSUPPRESSION FACTOR The immunosuppressive effect of UVB radiation has been acknowledged for a long time and it is thought to affect the progress of skin cancers however, a few discrepancies are due to the different UV sources. There are different patterns of sun exposure coupled with basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). Different mechanisms of immunosuppression have already been explained via Figure 6. The statistics pertaining to skin cancer risk drop by regular sunscreen use are inconsistent, for example, one random- ized assessment of sunscreen worth demonstrated statistically signifi cant protection for the development of SCC but no protection for BCC (69), whereas another randomized study verifi ed a poorer trend for manifold occurrences of BCC among sunscreen users (70) but no noteworthy decline in BCC or SCC prevalence (71). Immunosuppression also contributes to the formation of nonmelanoma (keratinocyte) skin cancers. This amplifi ed threat has been coupled to the intensity of immunosuppres- sion and UV exposure. Risk of cutaneous malignancy increases with the increased interval and dose of immunosuppressive agents the reverse effect is seen with decreased dosage, or after the removal of immunosuppressive factors. SPF is based on erythema, which is a poor indicator of immunosuppression (72). This brings up the subject whether the immune protection factor (IPF) of a sunscreen is equivalent to its SPF? According to few studies, sunscreen may provide insuffi cient immunoprotection in the prevention of skin cancer. Hence, the capacity of sunscreens to shield laboratory animals and humans against the immunosuppressive effects of UV radiation has been the area under discussion and great disagreement (73–75). The dose providing 50% immunosuppression (D50%) was calculated to be about fi ve MEDs (76). Wolf and Kripke (1998) brought out that application of different sunscreens with SPFs ranging from 3.5 to 5.7 afforded full immunoprotection up to 8 MED, whereas only one did so at 12 MED. They also concluded erroneously that sunscreens protected beyond their SPF. However, this conclusion generated much criticism, including major criticism being that IPFs were not determined in the investigation (76). Peguet-Navarro et al. (2000) ranked IPFs according to the sunscreen SPF. Research in- cluded determination of dose of UVB providing 50% inhibition of the mixed epidermal cell/lymphocyte reactions (D50%), in the presence or in the absence of the different sun- screens graphically. The IPFs for the sunscreens were determined as the ratio of D50% in the presence of sunscreen/D50% in the presence of the respective vehicle. In the same manner, the IPFs for the vehicles were estimated as the D50% in the mien of the vehicle/ D50% in the absence of any discussion. It is a really hard task to relate the SPF value of sunscreen to its IPF. Both values refer to a different biological occurrence and depend signifi cantly on their particular action spectra (77).