A novel in vivo test method for evaluating the infrared radiation protection provided by sunscreen products

Abstract

Background Infrared radiation (IR) exposure generates reactive oxygen species and induces matrix metalloproteinase‐1 expression in human skin. Moreover, while not as acute as ultraviolet radiation, repeated infrared irradiation can result in the photoaging of skin. Broad‐spectrum sunscreens can protect skin from IR, but no human in vivo test methods for the evaluation of sunscreens' IR protection effect have been developed. We aimed to develop such a method. Materials and Methods We included 155 Korean subjects in our three‐part clinical study. The IR reflectance of subjects' skin was measured using a benchtop model of an IR light source and a reflectance measuring probe. We measured the IR reflectance in relation to skin color and hydration level to set up our experimental conditions. We then calculated the infrared protection factors (IPFs) of cosmetic emulsions as the IR reflectance ratio between cosmetic sunscreen‐applied skin and non‐sunscreen‐applied skin and assessed the relationship between IPFs and the amount of sunscreen ingredients. Finally, this method was validated using several commercial sunscreen cosmetics. Results Skin color and hydration level did not influence the IR reflectance of subjects' skin. The IPFs of cosmetic sunscreens showed a positive correlation with the amount of inorganic sunscreen ingredients. Conclusion In this study, we developed a simple, fast, and ethically acceptable human in vivo test method for evaluating the IPFs of cosmetic sunscreens.

In vivo determination of the Infrared‐A protection factor on human skin

“…Originally, we performed a set of clinical evaluation method using a commercially available IR spectrometer that is used for mineral exploration in the field of geology. 38 Based on our previous research, measurement of the skin reflectance in the IR-A region was found to be not affected by the skin color or moisture content. However, the intensity of the light source employed for that study was approximately seven times higher than that of the IR-A in actual sunlight due to the fact it was not possible to control the intensity of our fabricated Ir device; this result in discomfort for the test subjects.…”

“…In our previous study, we developed an in vivo determination method for the IR-A protection factor on human skin. 38 However, the intensity of IR-A in the used device was too high to mimic actual IR-A irradiating human skin on the Earth's surface. In addition, the intensity of IR-A irradiating the Earth's surface changes with the season and location, and so it is necessary to obtain information regarding the IR-A intensity, such as an annual average or maximum.…”

“…The procedure followed for the IPF measurements was as that described in our previous study. 38 More specifically, the process is follows:…”

“…Previously, we introduced a clinical method for the evaluation of IR-A protection on the skin. 38 However, information relating to the IR-A light source systems, such as the basis for setting up the light intensity and the spectrum, was insufficient. In addition, no statistical verification process was employed to compare the average value and the 95% confidence interval, and insufficient information was available regarding the sample formulations.…”

Recent Trends of Sunscreen Cosmetic: An Update Review

“…In fact, the IR protection effectiveness of sunscreen has been investigated through the in vivo method. Kim et al (2019) evaluated the resistance to IR rays provided by sunscreen in 155 Korean volunteers, and recorded the IR reflectance of volunteer's skin using a benchtop model of an IR light source and a reflectance measuring probe [87]. The results showed that the infrared protection factor (IPF) in protected skin was greater than that of unprotected skin.…”