B5 Serum 4-week Clinical Study

The goal of this clinical study is to evaluate the soothing, moisturizing and skin barrier repair effects of two test products by measuring changes in multiple indicators before and after product use, including clinical assessment, non-invasive instrumental measurement, image analysis, lactic acid stinging test and participant self-assessment. It will also explore the residual effect after 2 weeks of discontinuation (only for Serum 2.0). The main questions it aims to answer are: * Do the two test products provide soothing, moisturizing and skin barrier repair benefits after 4 weeks of continuous use? * Can Serum 2.0 sustain its efficacy at 1 week and 2 weeks after stopping application? This is a single-center clinical efficacy study with a 2-week washout period. Approximately 124 healthy Chinese female participants aged 20-40 years will be enrolled and randomly allocated into 2 groups, with around 62 participants in each group. At least 40 participants per group will complete the clinical testing part, and 60 participants per group will complete the questionnaire part. Researchers will compare skin parameters at multiple time points: baseline (T0), immediately after use (Timm), 1 day after use (T1d), 1 week after use (T1w), 4 weeks after use (T4w), 1 week after discontinuation (T5w, Group A only), and 2 weeks after discontinuation (T6w, Group A only). Participants will: * Apply the allocated test product on the full face continuously for 4 weeks * Attend scheduled on-site visits to receive clinical assessment, instrumental measurement, image analysis, lactic acid stinging test and fill in questionnaires * Conduct skin status self-assessment at each visit