Quinine is used as a cosmetic ingredient that stimulates scalp blood circulation and helps prevent hair loss. In Korea, it is permitted for use in shampoos at concentrations of up to 0.5% as quinine salts, and in hair lotions at up to 0.2% as quinine salts. Its use in other types of cosmetic products is prohibited. There were no reports exist regarding the dermal absorption of quinine in cosmetic products, and an in vitro dermal absorption study was conducted in compliance with the guideline according to the Ministry of Food and Drug Safety (MFDS) of Korea. Prior to conducting the dermal absorption study, analytical methods were established using high performance liquid chromatography (HPLC) with multiple reaction monitoring (MRM) for the quantification of quinine in various matrices, including swabs, stratum corneum (SC), skin (dermis and epidermis), and 6% PEG of receptor fluid (RF). The quinine analytical method used in this study demonstrated excellent linearity (r² = 0.998-0.999), accuracy (87.6-107.82%), and precision (2.73-11%) in compliance with the validation guidelines. To evaluate the skin absorption of quinine in sahmpoo products, a Franz diffusion cell was utilized. Quinine (0.4% and 0.15%) was applied to mini-pig skin at a dose of 10 μl/cm². Following a 30-minute application period, an interim wash-out step was performed to simulate shampoo conditions for the gel formulation. After 24 hours of application, the skin was wiped with a swab, and the stratum corneum (SC) was collected using tape stripping. Subsequently, the mini-pig skin was sectioned into eight pieces, and receptor fluid (RF) samples were collected at 0, 1, 2, 4, 8, 12, and 24 hours. As a result, the total dermal absorption rate of quinine was determined to be 0.40 ± 0.09 μg/cm² (0.99 ± 0.23%) and 0.05 ± 0.03 μg/cm² (0.28 ± 0.19%) for the 0.4% and 0.15% gel formulations, respectively. These results can be utilized for the exposure assessment of quinine when used as a cosmetic ingredient.