A notable evolution within the cosmetic sector is the increasing reliance on botanical agents with empirical evidence of efficacy, commonly known as cosmeceuticals. Among these, Citrus limon (lemon) has emerged as a prominent ingredient in advanced skincare preparations like face serums, reflecting its extensive history in traditional wellness practices. This review offers a detailed examination of lemon's application in contemporary dermatology. We explore its complex phytochemical makeup, which includes L-ascorbic acid (Vitamin C), citric acid, a range of flavonoids such as hesperidin and eriocitrin, and volatile essential oils. The paper systematically investigates the biological mechanisms that justify its use in cosmetics, including its powerful antioxidant, collagen-promoting, skin-lightening, antimicrobial, and anti-inflammatory capabilities. We also confront the significant formulation hurdles, such as the chemical instability of its primary active compounds and safety issues like phytophotodermatitis. The discussion covers sophisticated formulation methodologies and delivery platforms designed to augment both stability and cutaneous bioavailability. Finally, the review delineates the critical physicochemical and biological criteria necessary for the robust evaluation of a finished lemon-infused serum. In summary, Citrus limon possesses a potent, multi-action profile ideal for skincare, yet its successful deployment in a safe and effective serum is wholly contingent upon advanced formulation science.