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.