The ISO 24443-2021 In Vitro Determination of the Content of Ultraviolet A Radiation (UVA) Photodamage Protection Sunscreens specifies an in vitro method for determining the photodamage protection performance of sunscreen products against UVA radiation. The standard details methods for measuring the UVA Protection Factor (UVA-PF) of sunscreens and introduces new test parameters such as Critical Wavelength and Light spectrum Absorbance Ratio to assess the protection ability of products within the UVA range. The standard emphasizes the use of static in vivo SPF results to calibrate the UV Spectrum Absorbance Linear dispersion and specifies limits on the dose of UVA exposure. This standard aims to provide a more comprehensive way of evaluating sunscreen products and help consumers understand the UVA protection effect of products more accurately.