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New Way to Improve UV Protection: the Critical Wavelength Method!
The frequency of sun protection failure raised the curiosity of P&G Beauty photobiologists. In July 2003, these researchers purchased 188 mass-market sunscreen products to evaluate the product claims and determine if the ingredients listed on the ingredient labels could support these claims.26 The analysis revealed:
• 90 percent of sunscreens now claim SPF 15 or higher, and 82 percent make UVA or broad spectrum protection claims.
• 44 percent of those labeled "broad-spectrum" failed to provide the necessary breadth of protection required for the claim based on their lack of ingredients with FDA-approved UVA filters.
• Because sunscreen label claims are not alwaysc onsistent with ingredients found to be protective, UVA testing and labeling needs to be standardized. Based on these results, it is clear that many currently marketed sunscreen products primarily protect against UVB, with some coverage against UVA. Only those containing adequate levels of FDA-recognized long wavelength UVA sunscreens should legitimately claim to provide "broad-spectrum" coverage. Ingredients that protect against UVA, including avobenzone and zinc oxide, fend off the higher wavelengths of UVA up to 400 nanometers.
Sunscreens are evaluated in terms of their ability to block mainly UVB via the SPF test. Erythema is used as the biological endpoint. However, we know that subclinical damage caused by UVA is also occurring and not being evaluated by this method. Both UVB and UVA need to be screened to guard the cutaneous immune system and avoid both acute and chronic cellular injury.
Insert figures A and B here)Amplitude (height of the curve) measures the degree to which a product absorbs UV, i.e., in vivo SPF. Breadth (width of the curve) reflects how broadly effective a product is across the UV spectrum. The wavelength below which 90% of the area under the whole absorption spectrum from 290 to 400 nm falls is the critical wavelength. The key is to cover more wavelengths with a broader, higher curve that delivers more UVAc overage, such as in Figure A
Dermatologists and scientists agree that sunscreen marketers should supplement SPF information with data regarding UVA protection. This would give people a better idea about the total level of protection the products provide. Therefore, in addition to the FDA required SPF test, P&G Beauty researchers have been subjecting their own UV moisturizers to a more comprehensive test that requires the formulas to protect skin from the breadth of ultraviolet light. In working to close the UVA protection gap, P&G Beauty scientists have proposed that the FDA adopt the critical wavelength as a meaningful method to assess UVA efficacy and a simple label to communicate UVA protection. Critical wavelength, proposed as a standard measurement, would establish a more meaningful indication of broad-spectrum protection when combined with the SPF test. Establishing a standardof UVB/UVA filtration for sunscreens would improve and simplify skin protection.
In the current proposal to the FDA, for broad-spectrum/UVA claim, a product must have a critical wavelength of 370 nm. Figure A (left) shows how much coverage a "broad-spectrum" product should provide. Figure B (left) shows the coverage provided by a UVB sunscreen. An absorbency curve that covers more wavelengths is the best way to characterize a sunscreen's broadspectrum efficacy. Critical wavelength is a relevant and reproducible in-vitro index of the breadth of UV photoprotection, and when combined with in vivo SPF, provides a complete profile of sunscreen product efficacy.