THE PROTECTIVE EFFECT OF A BROAD-SPECTRUM SUNSCREEN AGAINST CHRONIC UVA RADIATION IN HAIRLESS MICE - A HISTOLOGIC AND ULTRASTRUCTURAL ASSESSMENT

Long-wavelength UVA (>340 nm) has been shown capable of inducing derma l damage with chronic exposure. This study assesses the effect of a br oad spectrum (SPF-15) sunscreen containing avobenzone (Parsol 1789) in comparison to an oxybenzone-containing sunscreen. Albino hairless mic e were irradiated thrice weekly (100 J/cm(2)/exposure) for a cumulativ e dose of 8000 J/cm(2) after 32 weeks. Sunscreens were applied (2 mu l /cm(2)) to two groups of mice. The third group was unprotected, and a fourth served as a normal unirradiated control. Unprotected, irradiate d mice developed epidermal acanthosis and dermal elastic fiber hyperpl asia with increased glycosaminoglycans. Mice protected with the avoben zone-containing sunscreen had marginal epidermal hyperplasia but no ot her histologic damage. By contrast, mice protected with the oxybenzone containing sunscreen, surprisingly, had damage that exceeded what was seen in unprotected mice. Electron microscopy confirmed the histologi c findings and revealed further ultrastructural differences between th e treatment groups. The unexpected exacerbation of photodamage with th e oxybenzone-containing sunscreen was very likely not due to the oxybe nzone but rather to irritation induced by some component in the vehicl e. All SPF-15 sunscreens, by definition, must protect against sunburn. The consequences of chronic exposure may be quite different and are c linically relevant.