[en] BACKGROUND: The classical management of acne calls for prolonged oral and/or topical treatments; however, some patients request a rapid effect to make the papules disappear within a few hours or days. OBJECTIVE: To test the effect of a single overnight application of a paste containing 0.25% miconazole nitrate on acne papules, and comparison with the effect of the same but unmedicated paste. METHOD: Narrow-band reflectance spectroscopy was used to assess the changes in E index (erythema) after overnight application of the pastes. In the first study, a total of 117 acne papules were assessed in 15 adolescents. Measurements of the E index were performed at 24-h intervals for 4 days on acne papules and the surrounding normal-looking skin. The last two assessments were performed the mornings preceding and following, respectively, a single application of the medicated paste. The second part of the study consisted of a double-blind, split-face study on 25 adolescents with acne. They applied each of the two formulations on a randomized part of the forehead. A total of 161 acne papules received the medicated paste and 160 received the same but unmedicated paste. Measurements were performed the mornings before and after the overnight treatment. RESULTS: In the first part of the study, no significant daily difference was observed between the three series of pretreatment E indices, on both acne papules and normal skin. The treatment did not affect the E index of normal skin. By contrast, it decreased significantly the E index of the acne papules. The second part of the study also showed that the medicated paste significantly decreased the E index of acne papules. This effect was significantly (P < 0.05) superior to that of the unmedicated paste. CONCLUSION: A single overnight application of miconazole nitrate paste appears to reduce the erythematous aspect of acne papules.