Topical sunscreens applied to the skin act by absorbing and/or scattering incident UV radiation (UVR). The shape of the absorption spectrum is the fundamental attribute of a topical sunscreen. It is expressed as the extinction coefficient: the measure of the degree to which the sunscreen absorbs individual wavelengths across the terrestrial UVR spectrum (290-400 nm). Absorption is the product of the extinction coefficient, the concentration of the active ingredient, and the effective thickness of application on exposed parts of the body.
Sunscreens are regulated for specific formulations in most countries. In the EU, Japan, and South Africa they are regulated as cosmetics and in other countries (Australia, Canada and New Zealand) as drugs. Testing for toxic effects is mandatory in each country. Control in Europe is by a directive of the European Commission (2000). This mandates that labelling should include a full list of ingredients in decreasing order of concentration, and that this should be displayed on the containers of all cosmetics that include sunscreen formulations.4-7 Sunscreens are now readily available in most countries during all seasons. In Australia the availability of sunscreens has been maximised through sales tax exemptions and they are now available in workplaces, schools; their use by children is actively promoted.8-10
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