The common food spice oregano grows wild in the mountains of Mediterranean countries. In ancient Greece, oregano or its essential oil was used for the treatment of wounds, snakebites, spider bites, and respiratory problems. Respiratory uses dominated the medicinal history of oregano in medieval Europe, but in the nineteenth century, physicians in the Eclectic School (a medical movement that emphasized herbal treatment) used oregano for promoting menstruation.
In the 1990s, the concept of the yeast hypersensitivity syndrome (often called “systemic candidiasis,” or merely “candida”) became popular in alternative medicine circles. This theory states, in brief, that many people develop excessive levels of the yeast Candida albicans and subsequently experience allergic symptoms to the yeast in their body. The symptoms of this purported syndrome include common conditions such as fatigue and headache. A succession of anticandidal treatments have been offered as treatment. Oregano oil is one of the more recent of these products.
It is true that oregano oil is toxic to many different types of microorganisms, including fungi and parasites.1-15
However, the same is the case with hundreds of essential oils of herbs, not to mention vinegar, alcohol, and bleach. It is a long way from killing microorganisms in a test tube or on the surface of a block of cheese to medicinal effects in the body. Only double-blind, placebo-controlled studies in humans can prove a treatment effective, and none have been performed on oregano oil. Nonetheless oregano oil is widely marketed as a treatment for candida.
There is a related theory that many people suffer from undiagnosed intestinal parasites; oregano oil is marketed for treatment of this purported problem as well. Oregano oil is also advocated for dozens of other illnesses, ranging from asthma and HIV infection to rheumatoid arthritis, though without any reliable justification.
Websites selling oregano oil additionally point out that it has antioxidant properties. While true,16,17 this does not—by itself—indicate any health benefits. Most major studies of antioxidants have failed to identify the specific benefits that were once seen as likely to result from supplementation with these substances.
A typical dose of oregano oil is 100 mg three times daily of a product standardized to contain 55%–65% of the presumed active ingredient carvacrol.
There are no specific safety risks known to be associated with use of oregano oil products. However, in general, essential oils of herbs can be toxic when taken even in relatively small quantities. Allergic reactions are also possible.
Safety in young children, pregnant or nursing women, or people with severe liver or kidney disease has not been established.
1. Akgul A, Kivanc M. Inhibitory effects of selected Turkish spices and oregano components on some foodborne fungi. Int J Food Microbiol. 1988;6:263-268.
2. Burt SA, Reinders RD. Antibacterial activity of selected plant essential oils against Escherichia coli O157:H7. Lett Appl Microbiol. 2003;36:162-167.
3. Daferera DJ, Ziogas BN, Polissiou MG. GC-MS analysis of essential oils from some Greek aromatic plants and their fungitoxicity on Penicillium digitatum. J Agric Food Chem. 2000;48:2576-2581.
4. Dorman HJ, Deans SG. Antimicrobial agents from plants: antibacterial activity of plant volatile oils. J Appl Microbiol. 2000;88:308-316.
5. Elgayyar M, Draughon FA, Golden DA, Mount JR. Antimicrobial activity of essential oils from plants against selected pathogenic and saprophytic microorganisms. J Food Prot. 2001;64:1019-1024.
6. Fabio A, Corona A, Forte E, Quaglio P. Inhibitory activity of spices and essential oils on psychrotrophic bacteria. New Microbiol. 2003;26:115-120.
7. Force M, Sparks WS, Ronzio RA. Inhibition of enteric parasites by emulsified oil of oregano in vivo. Phytother Res. 2000;14:213-214.
8. Friedman M, Henika PR, Mandrell RE. Bactericidal activities of plant essential oils and some of their isolated constituents against Campylobacter jejuni, Escherichia coli, Listeria monocytogenes, and Salmonella enterica. J Food Prot. 2002;65:1545-1560.
9. Hammer KA, Carson CF, Riley TV. Antimicrobial activity of essential oils and other plant extracts. J Appl Microbiol. 1999;86:985-990.
10. Juglal S, Govinden R, Odhav B. Spice oils for the control of co-occurring mycotoxin-producing fungi. J Food Prot. 2002;65:683-687.
11. Lahlou M. Potential of Origanum compactum as a cercaricide in Morocco. Ann Trop Med Parasitol. 2002;96:587-593.
12. Lambert RJ, Skandamis PN, Coote PJ, Nychas GJ. A study of the minimum inhibitory concentration and mode of action of oregano essential oil, thymol and carvacrol. J Appl Microbiol. 2001;91:453-462.
13. Mejlholm O, Dalgaard P. Antimicrobial effect of essential oils on the seafood spoilage micro-organism Photobacterium phosphoreum in liquid media and fish products. Lett Appl Microbiol. 2002;34:27-31.
14. Nielsen PV, Rios R. Inhibition of fungal growth on bread by volatile components from spices and herbs, and the possible application in active packaging, with special emphasis on mustard essential oil. Int J Food Microbiol. 2000;60:219-29.
15. Sokovic M, Tzakou O, Pitarokili D, Couladis M. Antifungal activities of selected aromatic plants growing wild in Greece. Nahrung. 2002;46:317-20.
16. Martinez-Tome M, Jimenez AM, Ruggieri S, Frega N, Strabbioli R, Murcia MA. Antioxidant properties of Mediterranean spices compared with common food additives. J Food Prot. 2001;64:1412-1419.
17. Beddows CG, Jagait C, Kelly MJ. Preservation of alpha-tocopherol in sunflower oil by herbs and spices. Int J Food Sci Nutr. 2000;51:327-339.
Last reviewed December 2015 by EBSCO CAM Review Board Last Updated: 12/15/2015