Sun protection is a mystery, and not as easily solved as we once thought. The story starts with the classic slick of ZnO down a lifeguard’s nose, which was worn as a badge of summer honor and did a reasonably good job of physically preventing sunburn. The industry would eventually uncover that inorganic sunscreens mainly reflect in the UVA and absorb in the UVB range. The scene also changed when the visibly white sunscreen became esthetically undesired, and product developers found themselves shrinking TiO2 and ZnO particles to micro and nano sizes to make them imperceptible.
Enter: organic sunscreens, e.g., octocrylene, avobenzone and octinoxate, whose mechanisms were different and unlocked new secrets to effectively protect users. Taking their variety of efficacies across different wavelengths, along with those of inorganic filters, led to puzzle-piecing filters together for greater efficacy. Eventually, though, stability issues with organics came to light, prompting the need for photostabilizers and raising questions around their potentially sensitizing effects. Inorganics, too, were investigated for stability and safety issues. Indeed, the entire electromagnetic spectrum was taken into question, insofar as: which wavelengths cause what effects in the human body? which peripheral wavelengths, i.e., infrared and high energy visible light, are of concern? and even what alternative light sources, e.g., blue light emitting personal devices, should be assessed?
Positive biological effects from sun exposure also were revealed and in relation, the possible negative effects of screening out too much. Vitamin D production, for one, became a major focus and concern. More recently, connections between UV and the skin microbiome are under examination.1 As both can modulate the immune response, could one be at odds with the other?
This brings us to the focus of our current issue. As the sunscreen mystery has unfolded, identifying a consistent and accurate approach to measuring sun protection has become, at best, a moving target. The ISO in vivo test method, described by Pissavini, is viewed as the current gold standard. But as we have seen, change is inevitable as new evidence arises. So, despite reviews and updates to the gold standard, alternative approaches may be worth exploring; several are explored by Osterwalder, et al. Also offered this month are Expert Opinions on current and future sunscreens, and myths and more about sunscreens from renowned sunscreen researcher Brian Diffey, Ph.D. We hope the concepts examined here bring you one step closer to closing the sunscreen case; at least for now.
Rachel L. Grabenhofer, Managing Editor