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/cm(2) 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/cm(2) and 1 mg/cm(2) .

METHODS: Two SPF 45 sunscreens (one with a high level and one with a low level of UVA protection) were applied at 2 mg/cm(2) and 1 mg/cm(2) to four randomized 6 × 6 cm areas on the upper thorax of 15 female patients with a typical history of PLE. The areas were exposed daily to increasing UVA-UVB 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/cm(2) (P = 0.004). At 1 mg/cm(2) , 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/cm(2) .