Evaluation of Infrared Photoprotective Potential of Cosmetic Ingredients Using Directional-Hemispherical Reflectance in an Ex Vivo Model.

Background: Infrared (IR) radiation constitutes the dominant component of the energy reaching the Earth's surface and plays a significant role in the photochemical and thermal processes occurring in the skin. The aim of this study was to evaluate the photoprotective potential of selected cosmetic ingredients-ferulic acid, citrus pectin, and dextran-against IR radiation using the directional hemispheric reflectance (DHR) method in an ex vivo model. Methods: Formulations based on an amphiphilic carrier (Lekobaza) containing various concentrations of the tested substances were developed, and their optical and thermal properties were evaluated. Results: The results showed that the application of all formulations led to a statistically significant reduction in reflectance in the near- and mid-infrared range, indicating an increase in the absorption of radiation energy within the formulation layer. The strongest absorption effect was observed for ferulic acid, which-in addition to its antioxidant properties-exhibits the ability to absorb IR energy and dissipate it as heat. Pectin and dextran formed a water-binding hydrocolloid matrix on the surface, acting as a selective "water filter" for long-wavelength radiation (IR-B and IR-C). At the same time, all the tested systems increased the surface's thermal emissivity, which promotes more efficient dissipation of absorbed energy through radiative cooling and may support the skin's natural thermoregulation. Conclusions: The obtained data indicate that protection against IR radiation should not be defined solely as the physical reflection of radiation, but as a complex process of managing the skin's energy balance, encompassing surface absorption, heat dissipation, and the neutralization of biological effects. The results support the development of hybrid photoprotective systems combining antioxidant and thermoregulatory mechanisms to prevent thermal aging-related changes.