Thimerosal is widely used as a preservative in various medical and pharmaceutical products to prevent bacterial and fungal contamination. It is commonly found in vaccines, where it helps maintain sterility, especially in multi-dose vials, by inhibiting the growth of microorganisms. Additionally, it is used in some antiseptics, eye drops, nasal sprays, and contact lens solutions to ensure product safety and longevity. Historically, it has been used in certain cosmetics, though this is now limited. Its effectiveness at low concentrations makes it a practical choice for preserving the integrity of these solutions. However, its use has been reduced or eliminated in certain vaccines and other products due to concerns about potential health risks, particularly in pediatric formulations.