Background: Today, the sun protection factor (SPF) value of sunscreen products is determined in vivo with a standardized protocol (EN ISO 24444:2010), and the measured SPF biological end point is the visible skin erythema. However, many of the sunscreen products currently available on the market have antiphlogistic ingredients, which may potentially result in an overestimated SPF of the sunscreen. Aims: To investigate the potential influence of the antiphlogistic ingredients panthenol and bisabolol in sunscreens on the determined SPF value in vivo. Methods: Formulations with different concentrations of the antiphlogistic ingredients bisabolol or panthenol were tested. As a reference, a base formulation (vehicle) without antiphlogistic ingredients was used. First, the SPF of the sunscreen formulas with and without antiphlogistic ingredients was analyzed in vitro. To investigate whether the antiphlogistic ingredient may suppress the inflammatory response to ultraviolet (UV) irradiation, the SPF was determined in vivo. Finally, selected formulations were also analyzed in an erythema model for testing formulations on UV-induced inflammation. Results: It could be confirmed that no differences between the formula with and that without the active antiphlogistic ingredients bisabolol or panthenol exist when measured in vitro. However, there was also no statistically significant difference in the erythemal response between the vehicle (without an antiphlogistic active ingredient) and the test formulations with different concentrations of the antiphlogistic active ingredients in the in vivo determination of the SPF. Evidence of anti-inflammatory activity of the sunscreen antiphlogistics bisabolol and panthenol was also not apparent in the UV model over a time course of 48 h. Conlusion: The antiphlogistic ingredients panthenol and bisabolol incorporated in the tested sunscreen formula do not interfere with erythema reddening and thus do not affect the SPF value in vivo.

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