HPLC-DAD Determination of Hydroquinone, Salicylic Acid, and Niacinamide in Skin-Whitening Products: Method Validation and Safety Evaluation

Skin-whitening products (SWPs) are widely used, yet many contain prohibited or misdeclared depigmenting agents posing safety concerns. This study developed and validated a sensitive and reliable HPLC-DAD method for the simultaneous determination of hydroquinone (HQ), salicylic acid (SAL), and niacinamide (NIC) in commercial and homemade SWPs. Validation followed ICH Q2(R1), demonstrating good specificity, linearity (R2 > 0.9999), method precision (%RSD < 2%), and LOD/LOQ values of 0.2 and