Influence of the quantity of sunscreen applied on the ability to protect against ultraviolet-induced polymorphous light eruption

Background/Purpose Despite the fact that most people apply less sunscreen than the 2?mg/cm2 required to measure sun protection factor (SPF), there is a lack of clinical data on the protection afforded from lower applied quantities. The aim of this study was to compare the ability of sunscreens to protect against UV-induced polymorphous light eruption (PLE) when applied at 2?mg/cm2 and 1?mg/cm2. Methods Two SPF 45 sunscreens (one with a high level and one with a low level of UVA protection) were applied at 2?mg/cm2 and 1?mg/cm2 to four randomized 6?X?6?cm areas on the upper thorax of 15 female patients with a typical history of PLE. The areas were exposed daily to increasing UVAUVB radiation until a PLE reaction was detected or a maximum of five consecutive days. Results The proportion of patients who developed a PLE reaction with the high UVA-protection sunscreen was significantly lower (0%) than with the low UVA-protection sunscreen (73%) when both sunscreens were applied at 2?mg/cm2 (P?=?0.004). At 1?mg/cm2, 33% and 80% of patients presented a PLE reaction with the high and low UVA-protection sunscreen, respectively (P?=?0.064). Conclusion A high SPF and high UVA-protection broad spectrum sunscreen was able to protect the majority of patients from the development of UV-induced PLE reaction even at 1?mg/cm2.