Adv Exp Med Biol. 2014;810:429-63.
Sunscreens have become since more than 40 years the most popular means of protection against UV radiation (UVR) in Western countries. Organic and inorganic filters with different absorption spectrum exist. They filter or scatter UVR. Protection from UVB is quantified as a minimal erythema dose-based sun protection factor. UVA protection testing is less standardized: Persistent pigment darkening and critical wavelength are currently used methods. Marketing and labeling of sunscreens underlay national regulation, which explains major differences between the European and the US sunscreen market. Sunscreens are most performing in sunburn prevention. Broad-spectrum UVB and UVA protection and regular application in sufficient amounts are essential for prevention of skin cancers, UV-induced immunosuppression, and skin aging. A significant benefit from regular sunscreen use has not yet been demonstrated for primary prevention of basal cell carcinoma and melanoma. Concerning the prevention of actinic keratoses, squamous cell carcinomas, and skin aging, the effect of sunscreens is significant, but it remains incomplete.
Some organic UV filters (PABA derivatives, cinnamates, benzophenones, and octocrylene) have been described to cause photoallergy. Percutaneous absorption and endocrine disrupting activity of small-sized organic and nano-sized inorganic UV filters have been reported. On lesional skin and in pediatric settings, these products should be used with caution. Cutaneous vitamin D synthesis depending on skin-carcinogenic UVB radiation, the potential risk of vitamin D deficiency by sunscreen use has become a major subject of public health debate. Sunscreens indeed impair vitamin D synthesis if they are used in the recommended amount of 2 mg/cm2, but not in lesser thickness below 1.5 mg/cm2 that corresponds better to what users apply in real life conditions. Large molecular last generation UVB-UVA broad-spectrum sunscreens have a better benefit-risk ratio than former organic filters: They offer better protection in the UVA band, they are non toxic and non allergenic. A better outcome of sunscreen efficacy especially in primary skin cancer prevention may be achieved with these molecules.
Sun protection factors: worldwide confusion.
Br J Dermatol. 2009 Nov;161 Suppl 3:13-24. doi: 10.1111/j.1365-2133.2009.09506.x.
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 who 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.