Effects of sunscreen on skin cancer and photoaging

Application of sunscreen to the skin is widely used as an adjunct strategy, along with wearing protective clothing and seeking shade, to protect against skin cancer and photoaging that result from excessive sun exposure. Many epidemiological studies of case–control and cohort study design have studied the effects of sunscreen use on skin cancer, and more recently photoaging, but their findings have been mostly uninformative. This review of results of randomized controlled trials shows that the evidence, though limited, supports beneficial effects of sunscreen application on the occurrence of skin cancers and skin photoaging.     

Quantity of sunscreen used by European students

BACKGROUND: The ability of sunscreen products to delay sun-induced skin erythema is indicated by the sun protection factor (SPF), which is measured using an internationally agreed sunscreen thickness of 2 mg cm(-2). OBJECTIVES: To determine the thickness of sunscreen used under practical conditions. METHODS: In two double-blind randomized trials performed in five different places in Europe in 1997 and 1998, 148 18--24-year-old students received either an SPF 10 or an SPF 30 sunscreen to be used during their summer holidays. RESULTS: Complete, detailed data on quantities of sunscreen used and skin areas on to which sunscreen was applied were available for 124 students. The median thickness of sunscreen applied was 0.39 mg cm(-2). We found no variation in sunscreen thickness according to sex, skin phototype, study place or SPF. CONCLUSIONS: Our results indicate that most consumers do not benefit from the SPF indicated on sunscreen bottles, and do not support the idea that thickness of sunscreen applied would be greater if these products were cheaper. We suggest that information on ability of a sunscreen product to prevent sunburn should be adapted in order to reflect actual usage patterns.     

A double‐blind,randomized assessment of the irritant potential of sunscreen chemical dilutions used in photopatch testing*

Background: The maximum concentration of organic sunscreen filters in current usage that does not lead to irritant reactions when performing photopatch testing is not known. Such irritant reactions can be misinterpreted as positive photoallergic contact dermatitis reactions. Objective: To determine the frequency of irritant reactions to 19 organic sunscreen filters in current use. Patients/Methods: Ninety‐four healthy volunteers were photopatch tested using the European consensus methodology to three different concentrations (2%, 5%, and 10%) of 19 organic sunscreen filters at the Photobiology Unit in Dundee, UK. Results: Of the 94 subjects recruited, 80 were analysed after withdrawals and exclusions. Of the 19 organic sunscreen filters studied, only 2 compounds led to irritant reactions in ≥5% subjects. Five per cent and 10% benzophenone‐4 led to irritant reactions in four and six subjects, respectively. Five per cent methylene bis‐benzotriazolyl tetramethylbutylphenol led to irritant reactions in six subjects, but unlike benzophenone‐4, this was not in a dose‐dependent fashion. Conclusions: When performing photopatch testing according to the European consensus methodology with these 19 organic sunscreen filters, a 10% concentration is suitable for all filters, except benzophenone‐4, which should be tested at a concentration of 2%.