Acne vulgaris has anecdotally been attributed to diet by individuals affected by this skin condition. In a 2009 systematic literature review of 21 observational studies and 6 clinical trials, the association between acne and diet was evaluated. Observational studies, including 2 large controlled prospective trials, reported that cow's milk intake increased acne prevalence and severity. Furthermore, prospective studies, including randomized controlled trials, demonstrated a positive association between a high-glycemic-load diet, hormonal mediators, and acne risk. Based on these findings, there exists convincing data supporting the role of dairy products and high-glycemic-index foods in influencing hormonal and inflammatory factors, which can increase acne prevalence and severity. Studies have been inconclusive regarding the association between acne and other foods.