Internet herb stores claim that swallowing oregano oil can cure your cold or flu. But the devil's in the details. Oregano oil is an antimicrobial, and can even kill off that tough cruise ship plague, norovirus—but there's no evidence it can do so inside your body, scientists say. It works to inactivate pathogens before they get inside.
Researchers experimented on the mouse form of norovirus—genetically similar to the hard-to-grow human strain. They treated virus colonies with solutions of either four percent oregano oil, or half a percent carvacrol—the active ingredient.
Turns out oregano oil cut virus numbers by 10-fold. Carvacrol: 10,000-fold. In comparison, bleach achieves a million-fold reduction. The results appear in the Journal of Applied Microbiology. [D. H. Gilling et al., Antiviral efficacy and mechanisms of action of oregano essential oil and its primary component carvacrol against murine norovirus]
So, oregano oil's nowhere near as effective as bleach. But it's nontoxic, and has no noxious fumes. Unless you hate the smell of oregano. So study author Kelly Bright of the University of Arizona says it could be useful in food-safety settings: “You could maybe reduce the amount of bleach you're using by throwing in some carvacrol or essential oil.” Just don't expect it to cure you, once you've got the bug.
[The above text is a transcript of this podcast.]