Purpose Retinol is widely used for topical application for antiaging. However, the efficacy and effect rate of different concentrations of retinol have been rarely analyzed. Therefore, in this study, the efficacy and rate of effect of retinol concentrations from 1500 IU to 6600 IU, on various skin parameters, have been compared. Patients and methods Seventy-two Korean women aged 40 to 59 years participated in this study. Retinol was used by them for 24 weeks; the effects were measured at 0, 2,

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... , 8, 12, and 24 weeks. The measurement parameters for aging were crow's feet, forehead wrinkles, nasolabial fold, dermal density, and elasticity and that for skin color were skin brightness, yellowness, redness, and standard deviation of skin brightness. The texture of the skin was measured by measuring the skin roughness and pores, and the skin barrier function was evaluated through hydration, sebum, and desquamation. Results Low concentration retinol (1500–2500 IU) had a significantly higher effect in skin color, brightness, and elasticity and faster improvement rate in skin brightness and elasticity compared to that for high concentration (3300–6600 IU). High concentration of retinol had a significantly higher effect in wrinkles, dermal density and pores and faster improvement rate for wrinkles, skin texture, pores, and desquamation compared to that for low concentration. Conclusion This study evaluated the changes caused by different concentration of retinol over a long period of time. The results of this study have great implications as the optimal concentration of retinol can be prescribed for an accurate period for the desired results without side effects.