o-Phthalaldehyde, often abbreviated as OPA, is usually a pale yellow crystalline solid at room temperature and standard pressure. It is a highly effective disinfectant and high-level sterilant widely used in healthcare settings, especially for the disinfection of sensitive medical equipment that cannot withstand high temperatures. Compared with traditional glutaraldehyde, it acts faster, has better stability, and produces less irritating odor, making it a common alternative in endoscope reprocessing. It exerts its antimicrobial effect by destroying bacterial proteins and nucleic acids, showing strong activity against various bacteria, fungi, and viruses.