Thymol as a natural monoterpenoid antibacterial agent: a comprehensive review of applications and current advances

Thymol, a monoterpenoid phenolic compound, exhibits broad-spectrum antibacterial activity and is gaining increasing attention as a natural alternative to synthetic agents. Thymol appears to demonstrate high antibacterial efficacy against Gram-negative and Gram-positive bacteria, particularly resistant pathogens, through disruption of bacterial cell membranes, protein and enzyme inhibition, influencing DNA synthesis, and triggering oxidative stress mechanisms. Given these reported mechanisms and its broad-spectrum activity, thymol has been the subject of increasing research interest in recent years. The aim of this review is to comprehensively evaluate the antibacterial effects of thymol based on studies published between 2020 and 2025, identified through major databases including PubMed, Scopus, and Web of Science. Based on current literature, thymol appears to have strong potential as an antibacterial agent in diverse fields such as dermatological products, veterinary treatments, oral health formulations, food preservative systems, and agricultural biopesticide applications. In recent years, various encapsulation and controlled-release strategies have been developed to overcome the limiting characteristics of thymol, such as low water solubility, volatility, and chemical instability, which restrict its direct use in clinical and industrial applications. Studies using thymol in combination with various carrier systems, nanoparticles, and phenolic extracts have shown that the bioavailability of the compound is increased and, in some cases, synergistic antimicrobial effects can be achieved. However, the data indicates that studies have not progressed beyond the in vitro and in vivo levels. This finding reveals the need for more detailed clinical data to support the research on such valuable molecules, which are essential in today's world where resistant pathogens are dramatically developing. Current research shows that thymol is a promising natural agent with antibacterial properties and potential applications. Despite the promising in vitro and in vivo evidence, thymol lacks clinical validation data and standardized formulation protocols. The primary bottleneck appears to be its pharmacokinetic profile, low oral bioavailability (~ 16%) and a short plasma half life (~ 1.5 h), which must be addressed before meaningful human trials can be designed.