Optimizing the spectral absorption profile of sunscreens

Objective To investigate whether sunscreens provide optimal protection by exhibiting a uniform spectral absorption profile throughout the ultraviolet spectrum or by having a spectral profile in which absorption in the UVB waveband is greater than in the UVA region. Methods A sunscreen with a flat spectral absorption profile was compared with one of the same SPF in which the SPF to UVA protection was in the ratio of 3 : 1 in terms of protecting against erythema and chronic effects with different action spectra, as well as the total UV burden to the skin. Results A sunscreen with spectral profile in which absorption in the UVB waveband is greater than in the UVA region confers no benefit in terms of erythema (and endpoints with similar action spectra) than a sunscreen with the same SPF that exhibits uniform absorption at all wavelengths throughout the UV spectrum. More importantly, the ‘3 : 1 profile’ offers inferior protection when endpoints with other action spectra are considered, as well as resulting in a total UV burden to the skin that is about 5 times higher than sunscreen products showing a flat spectral absorption profile. Conclusion It may be tempting to believe that it is beneficial to increase the absorption of sunscreens in the UVB region relative to the UVA to reflect the fact that skin damage is associated more with UVB than UVA exposure. However, this belief is a fallacy and consumers are best served with sunscreens in which the spectral protection profile is uniform at all wavelengths throughout the UV spectrum.