Phytochemistry, Efficacy and Safety Evaluation of Polyherbal Insect Repellent Formulations

Insect-borne diseases continue to impose a substantial global health burden, particularly in tropical and subtropical regions where vector exposure is persistent. Although synthetic repellents such as N,N-diethyl-meta-toluamide (DEET) and pyrethroids remain effective, concerns regarding dermal irritation, neurotoxicity, environmental persistence, and emerging insect resistance have accelerated interest in plant-based alternatives. Polyherbal insect repellent formulations, which combine multiple plant extracts or essential oils, represent a promising strategy for achieving broad-spectrum protection with improved safety and sustainability. This review critically examines the phytochemical foundations, mechanisms of action, efficacy, formulation advances, and safety considerations associated with polyherbal repellent systems. Key bioactive constituents include volatile terpenoids (e.g., citronellal, linalool, eucalyptol), phenolics, flavonoids, alkaloids, and limonoids, which collectively exert olfactory disruption, neurophysiological interference, anti-feeding, and anti-oviposition effects. Laboratory and in vitro studies commonly demonstrate protection levels ranging from 70% to 95%, with efficacy strongly influenced by phytochemical composition and delivery system. Recent innovations such as nano-emulsions, gels, sprays, and transdermal platforms have markedly enhanced stability, controlled release, and duration of repellency. Safety evaluations generally indicate low dermal toxicity, minimal sensitization, rapid biodegradability, and reduced ecological impact compared to conventional synthetic agents. Nevertheless, significant challenges persist, including variability in phytochemical profiles, lack of standardized extraction and quality control protocols, limited long-term clinical data, and regulatory ambiguity. Addressing these limitations through rigorous phytochemical characterization, harmonized testing methodologies, and controlled human studies is essential for the translation of polyherbal repellents into reliable public health tools. Overall, polyherbal formulations offer a scientifically credible, eco-friendly alternative for integrated vector management.