In 2002, the National Rosacea Society assembled an expert committee to develop the first standard classification of rosacea. This original classification was intended to be updated as scientific knowledge and clinical experience increased. Over the last 15 years, significant new insights into rosacea's pathogenesis and pathophysiology have emerged, and the disorder is now widely addressed in clinical practice. Growing knowledge of rosacea's pathophysiology has established that a consistent multivariate disease process underlies the various clinical manifestations of this disorder, and the clinical significance of each of these elements is increasing as more is understood. This review proposes an updated standard classification of rosacea that is based on phenotypes linked to our increased understanding of disease pathophysiology. This updated classification is intended to provide clearer parameters to conduct investigations, guide diagnosis, and improve treatment.

SummaryAcne is estimated to affect 9Á4% of the global population, making it the eighth most prevalent disease worldwide. Epidemiological studies have demonstrated that acne is most common in postpubescent teens, with boys most frequently affected, particularly with more severe forms of the disease. This paper aims to provide an update on the epidemiology of acne worldwide. Recent general and institutional studies from around the world have shown that the prevalence of acne is broadly consistent globally (with the exception of specific populations, which are discussed). However, this review highlights that there is a wide range of disparate outcome measures being applied in epidemiology studies, and we emphasize the need to develop a widely accepted, credible, standard assessment scale to address this in the future. In addition we discuss special populations, such as those devoid of acne, as well as the impact of potential determinants of acne on disease epidemiology.Acne vulgaris, or acne, is a common condition with a wide range of potential harms and associated costs. The former include symptomatic discomfort, scarring, emotional and psychosocial distress, occupational consequences and potential psychiatric disturbances including depression and suicide. Identification of individuals at risk of these sequelae can contribute to reducing the morbidity associated with acne.The Global Burden of Disease Project estimates the prevalence of acne at 9Á4%, ranking it as the eighth most prevalent disease worldwide. 1,2This initiative established prevalence and disability data from primary research manuscripts and databases, and conducted subsequent data analysis with a Bayesian meta-regression methodology, providing a means to harmonize discordant data and to account for a lack of data in geographical, temporal or other demographic items.2 While this project uses primary research findings to inform global metrics, there has not been a recent attempt to collate and present the world literature on acne prevalence collected over the past decade and a half. The last such review of acne prevalence in both general and schoolaged populations comprised literature up to 1995.

Scientific advances are continually improving the knowledge of acne and contributing to the refinement of treatment options; it is important for clinicians to regularly update their practice patterns to reflect current standards. The Global Alliance to Improve Outcomes in Acne is an international group of dermatologists with an interest in acne research and education that has been meeting regularly since 2001. As a group, we have continuously evaluated the literature on acne. This supplement focuses on providing relevant clinical guidance to health care practitioners managing patients with acne, with an emphasis on areas where the evidence base may be sparse or need interpretation for daily practice.