Acne lesion counting has been used widely in the evaluation of new acne treatments as a change in facial acne lesions counts over time in an individual patient could reflect a true change. However, lesion counts are more valid in greater patient populations as planned in this study. Therefore, the lesion counts are defined as secondary efficacy criteria except during the maintenance phase for the population treated with azelaic acid. As described before, microcomedones are considered as precursor lesion. Moreover, their counts are constantly reduced during acne treatment and precede the clinical relapse. Therefore, microcomedones counts will be used in this trial as a marker of maintenance of therapeutic effect achieved during initial treatment phase.