1,3-Dimethylhydantoin is primarily used as an intermediate in the synthesis of biocides and disinfectants, such as chlorinated or brominated hydantoins, for water treatment systems including cooling towers and industrial water circuits. These derivatives effectively control the growth of bacteria, algae, and fungi by releasing active halogens (like chlorine or bromine) slowly when dissolved in water. The inherent stability of the hydantoin structure makes these biocides suitable for harsh industrial environments with high temperatures and varying pH conditions. It is also utilized in the production of preservatives for personal care products, such as lotions, creams, and soaps, leveraging the antimicrobial properties of the resulting compounds. Additionally, it serves as a key intermediate in the synthesis of pharmaceuticals and agrochemicals.