Challenges in Sun Protection.

Since time immemorial, people protected themselves from solar radiation. Limiting time in the sun by seeking shade or wearing clothing was a matter of course. In the early 20th century, tanned skin - a result of exposure to sunlight - was associated with good health. At the same time, however, one also had to protect oneself against the potential of excessive exposure to avoid sunburns. Around 1945, the first sunscreen products for protection against solar radiation became available. In the years to follow and up to the recent past, a vast number of different sunscreen filters were developed and incorporated into a wide variety of product formats. Frameworks regulating filter substances and preparations and methods to characterize sunscreen products' performance parameters were developed. Over the past 50-70 years, the perception regarding the tasks of sunscreen products changed several times. It was initially promoted as a lifestyle product and had the task of preventing sun-related erythema (tan without burn). Later, the prevention of skin cancer was added. Only in recent times, sunscreen products have been increasingly advertised and perceived as beauty and lifestyle products again. Also, the use of sunscreen products for antiaging purposes is now commonplace. The different intended purposes (averting harm and prevention) and the widespread use of topical sunscreen products have promoted many investigations and generated a vast and ongoing need for consumer and patient information and education. In the following review, we analyze and discuss current topics from conflicting areas, such as sun protection products (e.g., ideal sun protection products, sun protection metrics), product safety (e.g., nanoparticulate sunscreen filters, regulatory issues), application in everyday life (e.g., wish to tan, vulnerable cohorts), as well as controversies and future challenges (e.g., risks and benefits of UV radiation).