Eucalyptol, also known as 1,8-cineole, is a naturally occurring organic compound classified as a monoterpenoid. It is characterized by a bicyclic structure with a single ether group. As the name suggests, eucalyptol is most commonly associated with eucalyptus plants, particularly the Eucalyptus globulus species. It is known for its fresh, camphoraceous aroma and is used in various applications, including aromatherapy and traditional medicine.

Besides exhibiting antioxidant, analgesic and anti-inflammatory effects, eucalyptol is also a bronchodilator and is often used as an ingredient in over-the-counter cough and cold remedies due to its bronchodilating properties, which can help relieve respiratory symptoms of the sinuses. Furthermore, eucalyptol can pass the blood-brain barrier and hence can be used as a carrier to deliver drugs to the brain via a microemulsion system.