Specialists in the development of sun protection products have found them at the foot of their Christmas tree! Two new methods for calculating SPF (sun protection factor) have been approved by ISO.
Published in mid-December, after several years of development, these two alternative methods to the ISO 24444 standard are intended to get faster and more reliable results, while being more ethical and less expensive to implement.
Zero-human method
ISO 23675, known as the “double plate” standard, is the very first 100% in vitro SPF determination method published by ISO. In short, it does not require any human volunteers.
This method is applicable to sunscreen products in form of an emulsion or alcoholic one-phase formulation, excluding in form of a loose or compressed powder or stick. It can only be used for the determination of a static sun protection factor and is therefore strictly not applicable for the determination of water-resistance properties of a sun protection product.
Experts from the ISO group, which included a representative from Cosmetics Europe, believe this method represents a major step forward in terms of precision and speed. As a 100% in vitro method, its use should be preferred, according to the Commission Recommendation of 22 September 2006 relating to sun protection products [1] (currently under review).
An extended hybrid method
The second standard, ISO 23698, lays down in detail how to measure sunscreen efficacy via a hybrid method combining in vitro and in vivo tests.
Also known as Hybrid Diffuse Reflectance Spectrology (HDRS) method, it enables to determine the absolute spectral absorbance characteristics of a sunscreen product on skin to estimate sunburn and UVA protection.
It has the advantage of allowing the characterization of both the sun protection factor (SPF), the UVA protection factor (UVA-PF) and critical wavelength (CW) protection of sunscreen products without requiring biological responses.
It is applicable to all formulations that contain any component able to absorb, reflect or scatter ultraviolet (UV) rays and which are intended to be placed in contact with human skin. It is applicable for emulsions and single-phase products, however it has not been evaluated for use with powder forms sunscreen products.
