1,5,5-Trimethylhydantoin is primarily used as a key intermediate in the synthesis of biocidal and antimicrobial compounds, such as chlorinated hydantoins (e.g., 1-bromo-3-chloro-5,5-dimethylhydantoin or BCDMH). These derivatives serve as effective biocides in industrial water systems, including cooling towers and paper mill processes, to control microbial growth by targeting bacteria, fungi, and algae, thereby preventing biofouling and system degradation. It is also utilized in the production of disinfectants and preservatives for household, institutional cleaning products, personal care items (e.g., lotions, creams, soaps), and industrial liquids, offering stability and prolonged antimicrobial activity in aqueous environments.