Title : Sun protection, progress, myths, and inconsistencies
Contemporary culture takes for granted the fact that it is mandatory to protect human skin from the deleterious influence of the Sun’s electromagnetic spectra. This notion is quite new. The total history of Sun protection is less than 100 years, and the notion of the need for broad-spectrum products, including an adequate balance of UVA and UVB filters has not been for more than 30 years. The number of UV filters available, notably in the UVA range, because of security concerns of the regulatory authorities in different regions of the world and lack of enough data, has not increased with the necessary speed to compensate for other molecules not being used anymore, on grounds of their scarce photostability and/or sensitizing properties and/or sea contamination potential. Especially in the USA because of FDA requisites. The issue has become more and more serious as the manufacturer´s marketing demands have pushed the protection level to SPFs as high as 70, or even more. When science, and common sense, indicate it is nonsense to push forward. To test the ability of the different formulations and filters used in each product to protect, the gold standard today is the SPF “in vivo”, as obtained from ISO 24444:2020, and de SPF-UVA “in vitro” as obtained from the ISO 24443:2021. Even if in practice, with the former, severe discrepancies are found when inter-lab comparisons are made. The ISO committee has made efforts to standardize the irradiation source, skin types, application technics, etc. But, from the origin, the irradiation source standard corresponds to Northern Europe’s latitude at a certain time of the year and the day. The same type of concerns can be mentioned by the choice of Fitzpatrick’s skin type choice, when generalized to every other geographical and ethnic site. When UVA radiation “in vitro” testing is considered, an extension of the sources used for “in vivo” tests has been done in the standard (filtered Xenon-arc lamps) to test photostability, that need cooling of test substrates (PMMA roughened plates) to avoid incorrect results. This fact needs to use expensive equipment, limiting the number of laboratories able to perform the tests. We have demonstrated (in a limited number of cases) that a simple LED source, emitting in the correct UVA range can substitute much more expensive equipment, obtaining results within the required 95% confidence level established in ISO 24443. These results hint that other technical details (for example, the skills of the operators, ease of spreading of the formula to achieve a uniform film, the temperature on the surface while testing, etc.) are more decisive in the results obtained. None of the results presented intends in any manner to replace the recommendation to protect the skin with good sunscreens. Just to understand the limits of both the formulas and the test methods available.
What will the audience learn from your presentation?
I expect that the audience will gain some insights into the limitations of our knowledge and the correct interpretation of the information presented on the labels and advertising by marketers.
Our experimental results should induce other scientists to further check our conclusions, and make them possible in lower-income countries, to test sunscreen samples following ISO 24443.
Last, but not least, stimulate a critical view on established concepts in this domain.