Inter-observer agreement on acne severity based on facial photographs

Background The three-grade acne classification (mild, moderate, severe) is widely used to define the licensed indications of acne treatments, and for therapeutic decision-making in clinical practice, but its reproducibility has never been assessed. Methods Ten photographs of facial acne were scored independently by eight experts using the three-grade acne classification. We conducted a descriptive analysis of the results, based on graphical representation of the scores for each photograph. Results Inter-observer agreement on acne severity based on the three-grade acne classification was very poor. Conclusion The classical three-grade acne classification is poorly reproducible. A new rating tool accompanied by a clinical description of each severity level would be extremely useful.