New approaches in standardized sun protection factor determination of sunscreens

Messsystem zur in-vivo-Bestimmung des Lichtschutzfaktors von Sonnenschutzmittel. (Copyright: Charité) / Measurement system for in vivo sun protection factor determination of sunscreens. (Copyright: Charité)

In June 2019, a meeting of ISO committee "Cosmetics" (ISO/TC 217) working group "Sun protection test methods" (WG 7) was held in Brussels. Prof. Dr. Jürgen Lademann, head of the »"Center of Experimental and Applied Cutaneous Physiology" of the Charité and topic leader for medicine in the consortium 'Advanced UV for Life' was invited to present the latest research results on the non-invasive determination of the sun protection factor (SPF) of sunscreens.

To date, SPF values have been determined in special laboratories using a standardized measurement method on probands (in vivo). Skin treated with sunscreen is irradiated with a defined dose of ultraviolet (UV) radiation until sunburn occurs. The sun protection factor is determined from the irradiation dose and time. In other words, what is actually protected from by sunscreens is induced.

The Food and Drug Administration of the United States (FDA) and the European Union are urging the development of a method without skin damage. The ISO Committee 217 is therefore working on an international guideline for an in vitro method using artificial skin models instead of test persons. "Due to the specific texture of skin, such in vitro measurements have a significant disadvantage", Prof. Lademann knows. "The temperature and especially the biofilm of skin are very important for the application of sunscreens and their protective function. This cannot be achieved with plastic plates."

Together with the worldwide leader in skin testing equipment »Courage + Khazaka electronic GmbH and the manufacturer of dermatological care products »Hans Karrer GmbH, Charité develops a measuring system for non-invasive sun protection factor determination. Using light emitting diodes, UV radiation of a specific wavelength is applied via fibers to the sunscreen treated skin of test persons. Reflected and in the tissue scattered light is detected and the sun protection factor is determined directly – without time-consuming erythema assessment. "This measuring principle allows to consider the specific texture and reaction of skin without harming the probands", summarizes Prof. Lademann.

Thus, the project team convinced the ISO and was asked to advance the development and to characterize the measurement method as a possible standard process. The next step is a combination of the project team's non-invasive sun protection factor determination on test persons and a spectral analysis of the sunscreen product itself. "This hybrid method has a great advantage," comments Prof. Lademann. "Sun protection factors of 80 and 100 could be measurable in this way." According to the European Union, these high sun protection factors do not need to be listed - the upper limit here is 50+. However, such a measurement would be very important for cosmetics manufacturers. Sunscreens and their active ingredients can be characterized and their effects better understood. In order to exploit this potential, the project team also works on miniaturizing the measurement setups. "The compact UV LEDs provide a good basis for this", Prof. Lademann says. "Finally, we aim at a reliable, user-friendly and cost-effective system that will be used for ISO standardized sun protection factor determination of sunscreens".