Exposure to ultraviolet (UV) radiation is associated with a variety of harmful effects ranging from photoaging to skin cancer. UVB (290 to 320 nm) directly damages the cellular DNA leading to the formation of the 6-4 cyclobutane pyrimidine dimmers, and UVA (320 to 400 nm) indirectly damages the DNA via the production of oxygen radical species. In this review, we focused on the technological and scientific aspects of photoprotection using sunglasses and clothing while attempting to dispel some of the misconceptions. In addition to the basic knowledge relating to sunscreens, we reviewed the current guidelines for testing and labeling UVA protection around the world, controversies associated with nanoparticles, and future sunscreens actives waiting for the Food and Drug Administration approval. Lastly, we reviewed alternative agents, such as antioxidants, that can be used to supplement and augment photoprotection provided by sunscreens.

Summary The use of sunscreen is embedded in a hierarchy of sun protection strategies consisting primarily of sun avoidance by seeking shade and covering up with clothing. Sunscreens are, however, important means of protection; thus, understanding how they work and knowing their limitations are crucial. This review explains the role of ultraviolet (UV) filters, emollients, emulsifier systems and other components in a sunscreen, as well as trends in formulations in Europe, North America, Latin America, and Asia Pacific. Furthermore, it explains how sunscreen performance in terms of sun protection factor, UVA protection, and other metrics can be simulated. The role of sensory characteristics in assessing and improving compliance is also discussed. In the final chapter, Facts and Fiction, five of the most common myths about sun exposure and sun protection by sunscreen are debunked.

The Sun Protection Factor (SPF) is a very popular instrument in the marketing of sunscreens. Unfortunately it is often not understood how sunscreens work and where the limitations of the SPF are. A lot of aspects of the SPF are confusing, e.g. the race for higher and higher numbers, the effect on SPF when less sunscreen is applied and if sunscreen should be used at all because they may block the Vitamin D synthesis. All this has a negative impact on compliance by the consumer or patient which is the most important influence factor in sun protection. This paper explains how sunscreens work, how the SPF is determined and where the limitations of the current methods exist. The dynamic view of 'UV radiation applied' and the 'UV dose transmitted' through the sunscreen onto the skin as well as onto a substrate in vitro help in the understanding and are also promising approaches in the in vitro assessment. A variation of the in vitro assessment of a sunscreen is the in silico calculation based on the absorption spectrum of the UV filters and an assumption about the irregular sunscreen film on the skin. The sunscreen simulator program can be used to determine how the SPF is affected by applying smaller amounts of sunscreen. Besides the SPF, UVA protection is also discussed. The degree of UVA protection determines the quality of the overall UV protection, whereas the SPF is an indication of the quantity of protection. Furthermore other protection factors such as IPF, iSPF, RSF and p53, and the inhibition of the Vitamin D3 synthesis by sunscreens are also discussed. In conclusion it is shown that the accuracy and robustness of the SPF and other Protection Factors will improve significantly with the availability of true broad-spectrum sunscreens rather than conventional UVB-biased sunscreens, because uniform protection profiles lead to protection independent of the action spectrum of the endpoint and the UV-radiation source.

The magnitude and quality of UV protection provided by topical sun products have improved considerably over the past three decades. As our knowledge and understanding of sun protection requirements increases, product and testing technologies advance and new sunscreen molecules and technologies become available. The biannual London Sun Protection Conference has monitored this development over the last two decades. The 2009 edition of the conference (June 3 and 4) was entitled "Perfection of Protection". This paper, based on our talk given at the conference, tries to answer the question about the "ideal sunscreen" and explores four key requirements of good UV protection regarding where we stand on a ranking scale between poor and perfect, and what still needs to be done. Technology is leading with a rating of 80%, Assessment/measurement follows at 70%, Norms/standards around 50% and Compliance ranks only around 30% between poor and perfect. UV filters are the heart of the product technology. Besides UVB-filters, plenty of UV filters for UVA II and UVA I protection are now available in most parts of the world, except the USA. Although the Sun Protection Factor is well established and various methods have been developed for assessment of UVA protection, the performance measurement of sunscreens is still far from perfect. On the other hand, the high bar for achieving the highest UVA protection in the various classification systems released recently in Europe (2006) and the USA (2007) already helped to increase the protection considerably. The greatest problem however, remains poor compliance. Providing cosmetically pleasing formulations that people like to wear and communicating what sunscreens are and how they work are key elements in improving UV protection.

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