Oil of oregano is a natural substance extracted from the leaves of the oregano plant. It has antioxidant, anti-cancer, antibacterial, antifungal, and antiviral properties. It contains carvacrol and thymol, two compounds that can kill many types of microbes, including Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. It may also help prevent and treat Candida yeast infections.