In vitro Sun Protection Factors (SPFs) of Sunscreen and Skin Irritability

Kim, Seong Jin; Lee, Dae Sung; Won, Young Ho; Kim, Jong Won; Han, Eui Sik; Lee, Sun Hee

Abstract

BACKGROUND
Use of suncreen is strongly recommended to prevent the harmful effect by ultraviolet (UV) ray, and new diverse synthetic chemicals have been screened and put forward as effective UV filters. However, the most important aspect of developing a novel UV filter is safety. OBJECTIVE: This study aimed to find out if there was any correlation between a high in vitro SPF (Sun Protection Factor) index and skin irritation by using standardized formulations containing organic or inorganic, active sunscreen ingredients. METHODS: HRIPT (Human repeated insult patch test) was conducted on with fifty subjects (male to female ratio as 3: 2, average age was 21.6+/-2.9 years), and in vitro SPFs of sunscreen formulations were measured. Patch tested UV filters (UVA, UVB, and physical blockers) were butyl methoxy dibenzoyl methane (BMDM 2%, 5%), benzophenone-3 (2%, 5%), homosalate (10%, 20%), octyl methoxy cinnamate (10%, 20%), octyl salicylate (5%, 10%), octocrylene (10%, 20%), zinc oxide (10%, 20%)and titanium dioxide (10%, 20%). Skin bioengineering measurements for capacitance, erythema, laser doppler blood flow were carried out before and after HRIPT to compare the subjective observation errors of the conventional scoring system of skin irritation (ICDRG standard). To explore any photoirritability, phototoxicity or photoallergy, individual UV filters were photopatch tested with higher concentrations (5%, 20%) than those of usual photopatch sunscreen test series RESULTS: The range of in vitro SPF revealed from 3.6 to 52.8. A doubtful, rather transient, weak erythema (+0.5) was noted in eight subjects, though the apparent skin irritation reaction can be estimated at over +1 by ICDRG guideline was not found during the HRIPT. The weak erythemas were observed at 20% homosalate, 10% octyl salicylate, 5% octyl salicylate, 20% octyl methoxycinnamate, 10% octyl methoxycinnamate, 10% octocrylene, 20% octocrylene, 5% BMDM, respectively in frequency, thus UVB filters of high concentration were related to weak irritation. Nosignificant differences in the measured skin bioengineering parameters were detected between before and after the HRIPT. Photopatch test failed to find any photoirritability and photoallergy. CONCLUSION: Skin irritability due to high in vitro SPFs appeared to be minimal or remained within the safety margin. However, a weak irritation was suspected from the organic UVB filters under the higher concentration range than its recommended range by regulatory guidelines. As for the newly developed, diverse formulations of multi-organic UV filters claiming high SPFs, dermatologists could consider the potential irritation reactions when it is preferentially used within a population.