ALADIN (Acne Lesion And Density INdex): a novel tool for automatic acne severity assessment

Background Acne affects approximately 80% of adolescents worldwide, regardless of age, sex or ethnicity. Effective treatment depends on timely and accurate severity assessment. However, the lack of methodological standardization results in high inter- and intraobserver variability. A standardized and explainable grading tool is needed to support consistent acne severity evaluation. Objectives To develop an artificial intelligence-driven tool that quantifies inflammatory lesion count and density from facial images to calculate scores aligned with the Investigator Global Assessment (IGA) scale. Methods ALADIN (Acne Lesion And Density INdex) is designed as a simple mathematical model able to deliver reproducible and interpretable acne severity scores. We validated ALADIN retrospectively using two datasets: (i) a public dataset with predominantly severe cases of acne and (ii) a private dataset of mild-to-moderate cases. Validation results evaluated ALADIN against IGA and Global Acne Grading System (GAGS) scores, annotated by expert dermatologists. Results Lesion detection with ALADIN was evaluated using precision, recall, mean average precision and mean absolute error (MAE). Acne grading performance was assessed via Pearson/Spearman correlations, MAE and Cohen’s kappa. ALADIN’s performance aligned well with the interobserver correlation of dermatologists, achieving Pearson correlations of 0.58 vs. 0.56 and 0.65 vs. 0.65 (private and public datasets, respectively) for IGA scores, and 0.32 vs. 0.44 and 0.43 vs. 0.44 for GAGS scores. Conclusions ALADIN demonstrates consistent performance and excellent interpretability. Compared with manual scoring systems, it provides a streamlined, data-driven alternative capable of minimizing observer bias. When integrated into a medical device software, it can further aid in standardizing acne severity assessment and enhance patient monitoring. However, in this study, analyses were predominately carried out with White and Asian patients. Future work will validate and ensure robustness with darker skin tones.