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Sunscreens are designed to protect skin against the UV portion of the solar spectrum, which includes the UVB (290-320 nm) and UVA (320-400 nm) regions. UVB irradiation is almost entirely absorbed by the epidermis and causes erythema or sunburn, while UVA penetrates to dermal layers, produces tanning, and is predominantly responsible for photoaging.
Sun protection provided by a sunscreen is measured according to the approved U.S. Food and Drug Administration (FDA) in vivo method that utilizes erythema as a biological endpoint. Therefore, the sun protection factor (SPF) of a sunscreen is an index of protection against UVB irradiation only and does not indicate the level of UVA protection.
At the same time, the effective protection against UVA associated with cumulative skin damage is a very important element of sunscreen and antiaging products, which needs to be clearly communicated to the consumer.
A "broad spectrum" protection claim, according to the sunscreen tentative final monograph, is currently allowed for sunscreens products: (1) containing sunscreen actives with absorption spectra extending to at least 360 nm or above; and (2) that demonstrate meaningful UVA protection using appropriate testing procedures to be developed.
It should be noted that, in contrast to the SPF, there is no standard method to measure photoprotection of a sunscreen product against UVA and such a method is still under consideration by the FDA. Presently, in the United States there are only three FDA-approved sunscreen actives that absorb in UVA region: avobenzone, titanium dioxide and zinc oxide. This fact limits the formulator’s ability to develop sunscreens that effectively protect against UVA and UVB.