Measuring ultraviolet A protection in sunscreen products

Abstract

To the Editor: The results concerning ultraviolet A light (UVA) protection in United States (US) sunscreen products compared with the UVA guidelines for sunscreens in the European Union (EU) published in the Journal by Wang et al1Wang S.Q. Xu H. Stanfield J.W. Osterwalder U. Herzog B. Comparison of ultraviolet A light protection standards in the United States and European Union through in vitro measurements of commercially available sunscreens.J Am Acad Dermatol. 2017; 77: 42-47Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar deserve comment. This study used two in vitro UVA protection tests, the US Food and Drug Administration (FDA) measurement of critical wavelength276 Federal Register27591 (2012) (codified at 21 CFR §201.327).Google Scholar (CW) and the International Organization for Standardization (ISO) method for UVA effectiveness testing,3International Organization for Standardization website. ISO 24443:2012. Determination of sunscreen UVA photoprotection in vitro. Available at: https://www.iso.org/standard/46522.html. Accessed May 22, 2017.Google Scholar which measures CW and also provides a calculated in vitro UVA protection factor (PF). Nineteen of 20 sunscreens met the US requirement of CW ≥370 nm, but only 11 of 20 were found to meet the EU desired ratio of UVA PF to sun protection factor (SPF) of 1:3.4The Commission of the European Communities. Commission Recommendation of 22 September 2006 on the efficacy of sunscreen products and the claims related thereto. Official Journal of the European Union, L265/39, 26.9.2006.Google Scholar The authors concluded that the majority of sunscreens tested with these in vitro methods offered adequate UVA protection according to US FDA requirements for broad spectrum status, but almost half did not pass the 1:3 UVAPF:SPF ratio recommended in the EU. Interestingly, all but 1 product that “failed” to meet the EU UVA PF ratio recommendation at SPF ≤60 contained zinc oxide with or without titanium dioxide. “Particulates” do not perform well in the optical in vitro UVA PF test, a key consideration in assessing the results obtained. This is a reason why the human clinical (in vivo) ISO UVA PF test is often recommended and preferred for formulations containing particulate, inorganic sunscreen ingredients. ISO has published both an in vivo UVA method5International Organization for Standardization website. ISO 24442:2011. In vivo determination of sunscreen UVA protection. Available at: https://www.iso.org/standard/46521.html. Accessed May 22, 2017.Google Scholar (conducted on skin, similar to SPF tests) and an in vitro optical method3International Organization for Standardization website. ISO 24443:2012. Determination of sunscreen UVA photoprotection in vitro. Available at: https://www.iso.org/standard/46522.html. Accessed May 22, 2017.Google Scholar using a quartz plate substrate; the results were spectrally measured via spectrophotometer. The in vitro test clearly has the benefits of being faster and cheaper. In theory, both methods should give the same result, but in fact the in vitro UVA test does not measure the UVA PF correctly for several product types (powders, sticks, or formulas containing particulate ingredients, such as zinc oxide). This is a recognized issue with the in vitro UVA PF method. The in vitro UVA test generally works well for lotion-type formulations containing only “organic” (ie, “chemical”) sunscreen actives, offering good correlation between in vitro and in vivo results for those formulas. Most US companies that market products globally formulate to meet or exceed global requirements for both SPF and UVA protection. To ensure that products and formulas meet EU or other regional requirements for the 1:3 ratio for UVA:SPF, the appropriate UVA test to confirm an accurate UVA PF should be conducted. For products containing certain particulates—zinc oxide or titanium dioxide—both the in vivo and in vitro UVA tests should be conducted. In my experience, the ISO in vitro UVA test often produced lower UVA protection values versus in vivo UVA tests for these formula types. In my opinion, that is a shortcoming in the Wang et al study.1Wang S.Q. Xu H. Stanfield J.W. Osterwalder U. Herzog B. Comparison of ultraviolet A light protection standards in the United States and European Union through in vitro measurements of commercially available sunscreens.J Am Acad Dermatol. 2017; 77: 42-47Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar The failure to meet the 1:3 UVA:SPF requirement for zinc oxide–containing formulas should be questioned, because the in vitro UVA test can give erroneous results for that type of formula. Comparison of ultraviolet A light protection standards in the United States and European Union through in vitro measurements of commercially available sunscreensJournal of the American Academy of DermatologyVol. 77Issue 1PreviewThe importance of adequate ultraviolet A light (UVA) protection has become apparent in recent years. The United States and Europe have different standards for assessing UVA protection in sunscreen products. Full-Text PDF