The task of the first sunscreens was to prevent the development of sun- burn and, following the spirit of the 1950/60s, not impair tanning of the skin. The need to quantify the protective performance soon arose.

Originally, with the help of natural, and now artificial, sunlight, a method was developed to determine a sun protection factor (SPF). It is formally defined as the ratio between the minimum erythema-effective UV dose on sunscreen-protected skin and minimum erythema-effective UV dose on unprotected skin and is today included in ISO standard 24444:2019.

Since the delineation of the first method for characterizing sunscreen performance in the 1950s, various guidelines of regulatory nature have been developed in  the different regions of the globe.

With harmonizing measures, attempts are being made to overcome the methodological differences that have developed. However, regardless of this, a number of challenges concerning the characterization of sunscreen performance remain that affect the methodology of all these guidelines equally.

On the one hand, these are method-internal issues, such as

1. light quality: natural vs. artificial sunlight
2. irradiation: dose vs. intensity
3. product application (laboratory vs. everyday life.

On the other hand, there are method-external issues, including:

1. inter-laboratory variability
2. discriminatory ability
3. erythema-induced burden on the test subjects.

The authors discuss current experiences and findings with the standardized methods and possible further developments.

Read more…

By IFSCC