This study aimed to evaluate the effect of adding extracts obtained from by-products on the physicochemical and functional properties of cleansing gels. Micellar extraction (2% decyl glucoside solution in water) was performed on secondary raw materials: banana peel (BP), pomegranate peel (PP), tomato pomace (TP), and grape pomace (GP). The extracts were analyzed for soluble substances and active compounds (polyphenols, carotenoids, and vitamin C). Cleansing gels containing plant extracts were also prepared and evaluated for their color and physicochemical and functional properties. The extracts contained natural polyphenols (10.99–16.54 mg·100 mL−1), carotenoids (1.391–2.402 mg·mL−1), and vitamin C (0.651–1.529 mg·100 mL−1). The extract-enriched gels showed altered color (lower brightness, greater redness and yellowness), enhanced foaming properties, and modified viscosity (402.9–416.8 mPA for BP and GP; lower for PP and TP). The pH of the gels ranged from 5.391 to 5.917, which is within the physiological range of human skin. Dissolution times were reduced by up to 60% compared to the control, with PP extract producing the shortest time of 15.7 min. These results indicate that plant by-product extracts can improve both the functional performance and skin compatibility of cleaning gels.