Background: Acne, the most common skin disease characterized by comedones, papules, pustules, nodules, and/or cysts, has a prevalence of 90% during adolescence. The pathogenesis of acne vulgaris requires further study based on the pathological and pathophysiological changes in acne. Recent findings and evidence: Adolescence is the period when teenagers have very high nutritional demands. The occurrence of acne during adolescence suggests that the patient is nutritionally deficient or has increased nutritional requirements. Malnutrition of vitamins（niacin） is the most important cause of abnormal metabolism and inflammation. A pellagra diagnosis should focus on the presence of the "3 D’s"（diarrhea, dermatitis and dementia）. The clinical features of acne include "3 D’s": dermatitis（acne, seborrheic dermatitis）, dyspepsia, and depression. Patients with acne are frequently associated with abnormal serum lipid profiles and elevated sebum secretion. Foam cells are an important pathological change in acne lesions. Niacin is the only vitamin that promotes the efflux of cholesterol and other lipids from cells and prevents foam cell formation. Foam cells in acne lesions suggest that patients with acne are deficient in niacin. Recently,several studies have reported the efficacy and safety of nicotinamide and niacin for acne treatment. Summary: Based on an analysis of the clinical feature of acne patients, pathological changes in acne lesions and the therapeutic effects of niacin on acne,we propose that acne can be diagnosed as a specific clinical type of pellagra, and niacin is the first choice for the treatment of acne vulgaris.