How to measure UVA protection afforded by sunscreen products

The availability of new and highly potent UVA filters represents a major advance in the development of sunscreen products able to efficiently protect against a number of adverse effects induced by UVA radiation, including erythema, premature skin aging, photosensitivity disorders and some forms of skin cancer. Sunscreens are evaluated with sunburn as the end point using the sun-protection factor method. The action spectrum for sunburn is heavily weighed in the UVB range with a small contribution from the UVA (320–400 nm). It is recognized that the UVA protection effectiveness of sunscreens cannot be assessed with the sun-protection factor method. It has also been recognized that a need exists to develop a robust method to evaluate the effectiveness of UVA sunscreens. This review discusses the current in vivo and in vitro UVA test methods and the science behind them.