Supplementary Material for: The Singapore/Malaysia Cross-sectional Genetics Epidemiology Study: An Updated and Detailed Analysis of Acne Vulgaris Severity, Scarring, and Phenotypes and Their Associated Risk Factors Among Young Chinese Adults

Introduction: Despite the high prevalence of acne vulgaris and its impact on affected individuals, few studies have provided a detailed characterization of acne phenotypes and their associated risk factors. This study aims to comprehensively evaluate the prevalence, severity, scarring, and phenotypes of acne, along with their associated risk factors, in a cohort of young Chinese adults, as part of the Singapore and Malaysia Cross-Sectional Genetic Epidemiology Study (SMCGES). Methods: Participants were randomly and consecutively recruited from universities in Singapore and Malaysia. Data on sociodemographic, familial medical histories of atopic diseases and acne, and lifestyle habits were collected using a validated investigator-administered questionnaire from 6225 young Chinese adults (mean age = 22.8 ± 5.7 years). A subset of participants underwent clinical assessment for acne severity (n = 2345), scarring grade (n = 2345), and phenotypes (n = 1191) by dermatologically trained personnel. Results: The prevalence of acne was 56.0%. Among acne cases (n = 3504), 38.5% had moderate-severe acne, 52.8% had scarring, 95.7% presented with blackhead and/or whitehead, and 55.8% had inflammatory phenotypes (e.g., papules, pustules, cysts and nodules). A parental history of acne emerged as the strongest risk factor associated with all acne phenotypes. Pet ownership (Adjusted odds ratio [AOR]: 1.403, 95% Confidence level [CI]: 1.131-1.744, p < 0.05) and occasional alcohol consumption (AOR: 1.328, 95% CI: 1.090-1.617, p < 0.05) were associated with a higher odd for blackhead and/or whitehead. Protective factors included higher parental education levels for acne scarring (AOR: 0.650, 95% CI: 0.459-0.904; p < 0.05), male gender (AOR: 0.365, 95% CI: 0.298-0.446; p < 0.05) and birthplace (AOR: 0.674, 95% CI: 0.555-0.819; p < 0.05) for non-inflammatory phenotypes. Conclusions: This study, conducted in a well-defined cohort of young Chinese adults from the SMCGES, reinforces familial history as a key risk factor for acne onset, severity, scarring, and phenotype manifestation. The identification of modifiable and environmental factors associated with acne phenotypes offers valuable insights for targeted interventions to improve acne management and control.