Integrated Phytochemical Characterization, Formulation Engineering, and Stability Assessment of a Spray-Based Dermocosmetic Delivery System Incorporating Plectranthus amboinicus Leaf Extract

The increasing demand for natural and sustainable cosmetic ingredients has stimulated interest in medicinal plants as sources of multifunctional bioactive compounds. This study aimed to develop and evaluate a low-viscosity spray-based cosmetic formulation containing Plectranthus amboinicus leaf extract through phytochemical characterization, antioxidant evaluation, formulation engineering, and physicochemical stability assessment. The novelty of this work lies in evaluating the feasibility of incorporating P. amboinicus extract into a spray-based delivery system while maintaining acceptable physicochemical formulation stability. Ethanol extracts were characterized for extraction yield, total phenolic content (TPC), and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity. Four formulations containing 0%, 1%, 3%, and 5% (w/v) extract were evaluated for appearance, pH, homogeneity, and short-term stability. The extract exhibited measurable antioxidant activity and detectable phenolic content. All formulations remained homogeneous, showed no phase separation, and maintained physiological skin pH (5.5–6.0) throughout storage. Only the 5% formulation showed a slight reduction in transparency without compromising physical stability. These findings demonstrate the feasibility of incorporating P. amboinicus extract into a spray-based cosmetic formulation while maintaining acceptable short-term physicochemical stability. The study provides preliminary formulation evidence rather than biological efficacy, and further phytochemical, rheological, spray-performance, biological, and long-term stability studies are warranted. Accordingly, the present findings demonstrate formulation feasibility only and should not be interpreted as confirmation of clinical skin benefits, dermocosmetic efficacy, or spray-device performance.