Sunscreens - Which and what for?

It is well established that sun exposure is the main cause for the development of skin cancer. Chronic continuous UV radiation is believed to induce malignant melanoma, whereas intermittent high-dose UV exposure contributes to the occurrence of actinic keratosis as precursor lesions of squamous cell carcinoma as well as basal cell carcinoma. Not only photocarcinogenesis but also the mechanisms of photoaging have recently become apparent. In this respect the use of sunscreens seemed to prove to be more and more important and popular within the last decades. However, there is still inconsistency about the usefulness of sunscreens. Several studies show that inadequate use and incomplete UV spectrum efficacy may compromise protection more than previously expected. The sunscreen market is crowded by numerous products. Inorganic sunscreens such as zinc oxide and titanium oxide have a wide spectral range of activity compared to most of the organic sunscreen products. It is not uncommon for organic sunscreens to cause photocontact allergy, but their cosmetic acceptability is still superior to the one given by inorganic sunscreens. Recently, modern galenic approaches such as micronization and encapsulation allow the development of high-quality inorganic sunscreens. The potential systemic toxicity of organic sunscreens has lately primarily been discussed controversially in public, and several studies show contradictory results. Although a matter of debate, at present the sun protection factor (SPF) is the most reliable information for the consumer as a measure of sunscreen filter efficacy. In this context additional tests have been introduced for the evaluation of not only the protective effect against erythema but also protection against UV-induced immunological and mutational effects. Recently, combinations of UV filters with agents active in DNA repair have been introduced in order to improve photoprotection. This article reviews the efficacy of sunscreens in the prevention of epithelial and nonepithelial skin cancer, the effect on immunosuppression and the value of the SPF as well as new developments on the sunscreen market. Copyright (C) 2005 S. Karger AG, Basel

Synthesis of mono-dispersed spherical silica particles containing covalently bonded chromophores

Organic–inorganic ultraviolet (UV) active hybrid materials have been prepared by a sol-gel process from benzophenone derivatives and tetraethylorthosilicate. The silica particles are spherical in shape and have a narrow size distribution which remains unchanged up to organic chromophore concentrations of 0.2 mmol g)1. At higher concentrations the spheres become less regular and fuse. A dependence of the material absorption properties on the particle size (at the same organic chromophore concentration) and on the concentration of surface grafted chromophores was noted. The most effective UV filter materials were found in a combination of silica incorporated chromophores and surface grafted chromophores at an overall low chromophore concentration. A comparison of the photostability of chromophores at standardized UV irradiation revealed an increase in stability for silica incorporated and surface immobilized benzophenone compared to benzophenone in a homogeneous solution