In vivo determination of the sun protection factor (SPF)

The ISO 24444 standard covers the analysis method for the in vivo determination of sunscreen products, SPF, that is, sun protection factor. The analysis method is performed on products that contain any component that can absorb, reflect or scatter ultraviolet (UV) rays and are intended to come into contact with human skin.

ISO 24444 provides the essential requirements for evaluating sunscreen products for the protection of human skin against erythema caused by solar ultraviolet rays. It is a laboratory method using a xenon arc lamp solar simulator or equivalent with known output to determine the protection performance of sunscreens against erythema on human skin due to solar ultraviolet rays.

In the SPF test method, the area between the scapula line on the back and the waist is determined as the test area. In the test processes, a part of the skin of the volunteer subjects is exposed to ultraviolet light without any protection, while a different part is exposed to ultraviolet light with the sunscreen sample to be tested.

After 16 - 24 hours after the test application, it is evaluated visually in terms of the presence of erythema that may occur after UV radiation.