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Scientific research on oregano oil and its components

This section was created to highlight studies on some of the health properties sources say oregano oil and its components possess. We are citing clinical trials, experiments and research related to specific medicinal properties of oregano oil and its components.

In a study conducted at the College of Food Science and Nutritional Engineering at the China Agricultural University in September 2008, researchers investigated the antibacterial action of carvacrol and thymol against Escherichia coli (Xu, et al., 2008). They concluded that carvacrol and thymol were effective in inhibiting the growth of E.coli through permeabilizing and depolarizing the cytoplasmic membrane.

Scientists studied the effects of cinnamon, thyme and oregano essential oils against foodborne microorganisms such as gram-negative bacteria Escherichia coli, Yersinia enterocolitica, Pseudomonas aeruginosa, and Salmonella choleraesuis, gram-positive bacteria Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus, and Enterococcus faecalis, molds Penicillium islandicum and Aspergillus flavus and yeast Candida albicans and concluded that the minimum inhibitory concentrations against these pathogens of oregano oil were generally lower than the other oils (Lopez, et al., 2007). They also concluded that carvacrol and thymol, both in oregano oil, along with cinnamaldehyde had the strongest antimicrobial effects among all the compounds they studied.

Researchers tested the potency of 11 commercially-available essential oils against 189 gram-negative and 135 gram-positive strains of locally prevalent pathogenic bacteria isolated from severely infected children in vitro (Hersch-Martinez, et al., 2005). The study suggested that Origanum vulgare was one of the top 3 that exhibited the highest and broadest antibacterial effects against the tested pathogens with Cinnamomum verum and Thymus vulgaris being the others.

Researchers at the University of Cordoba in Spain conducted an in vitro assay to analyze the activity of 5 essential oils against poultry-origin strains of Escherichia coli, Salmonella enteritidis and Salmonella essen, as well as pig-origin strains of enterotoxigenic E. coli (ETEC), Salmonella chloraesuis and Salmonella typhimurium (Peñalver, et al., 2005). The study showed that Origanum vulgare had the highest antimicrobial activity against all Salmonella strains with a minimum inhibitory concentration of 1%. On the other hand, all the essential oils including Origanum vulgare had an MIC of 2% against the 2 E.coli strains.

There has been a study at the Department of Pharmacognosy & Chemistry of Natural Products at the School of Pharmacy in Greece of the effect of Greek herbal medicines, including oregano oil against gastric ailments and peptic ulcer and it was determined that along with other herbs, Origanum vulgare was active against 1 standard strain and 15 clinical isolates of Helicobacter pylori (Stamatis, et al., 2003).

Researchers studied the effect of various monoterpenes from essential oils, including alpha-terpineol and thymol also found in oregano oil on herpes simplex virus type 1 (HSV-1) in vitro and determined that it can inhibit the virus by more than 80% using direct inactivation of free virus particles (Astani, et al., 2009).

Anti-allergy and anti-inflammatory
Scientists studied the potency of rosmarinic acid in perilla extract (also a component of oregano oil) against allergic asthma at the Health and Bioscience Laboratories in Japan (Sanbongi, et al., 2004). They used house dust mite allergens to sensitize C3H/He mice. They first administered Dermatophagoides farina directly to the trachea and after pulmonary eosinophilic inflammation and increased lung expression of IL-4 and IL-5 manifested in the test subjects, treated them orally with 1.5 mg of rosmarinic acid per day. The researchers observed that rosmarinic acid decreased the eosinophils in the lungs and airway and inhibited the expression of IL-4 and IL-5 and eotaxin in their lungs suggesting that rosmarinic acid was effective against allergic asthma, possibly because it enhanced the increases in cytokines, chemokines and allergen-specific antibody.

In the same laboratory in Japan, scientists also studied how orally administered rosmarinic acid can inhibit seasonal allergic rhinoconjunctivitis (SAR) (Osakabe, et al., 2004). Rosmarinic acid or placebo was given to patients and recorded symptoms, as well as profiles of infiltrating cells and concentration of cytokines in nasal lavage fluid. They observed a significant decrease in the symptoms, as well as in the number of neutrophils and eosinophils in the nasal lavage fluid of those treated with rosmarinic acid. They also concluded that the said effects were due to the inhibition of inflammatory response and the scavenging of reactive oxygen species.

Scientists conducted a study on the inhibitory action of carvacrol against cyclooxygenase-2 (COX-2) in a controlled environment to determine the anti-inflammatory effects of the said compound (Landa, et al., 2009). The results of the experiments demonstrated non-selective inhibition of the COX-2 isoforms, which suggest possible anti-inflammatory potential of carvacrol.


600 mg Origanum vulgare or wild oregano emulsified oil was given to 14 adult patients who tested positive for enteric parasites particularly Blastocystis hominis, Entamoeba hartmanni and Endolimax nana daily for 6 weeks (Force, et al., 2000). 8 of the 14 adult patients showed complete disappearance of the 3 parasites (4 cases of E.hartmanni, 1 case of E.nana and 8 cases of B.hominis) and decline in 3 cases. Also, of the 11 patients with B.hominis, 7 experienced an improvement in the gastrointestinal symptoms.

Using the method chequerboard microdilution, scientists studied the antifungal activity of thymol, a component in oregano oil against fluconazole-sensitive and –resistant strains of Candida albicans and found it effective against 24 fluconazole-resistant and 12 fluconazole-susceptible clinical isolates of Candida albicans (Guo, et al., 2009). They also observed a high percentage of synergistic effect that thymol produced with fluconazole and amphotericin B separately, against fluconazole-resistant and –susceptible strains of Candida through spectrophotometry of the assay, assessed using fractional inhibitory concentration index (FICI) and DeltaE models.


Researchers studied how a single dose or 15 daily doses of Origanum vulgare would affect the blood glucose levels in both normal and streptozotocin (STZ) diabetic rats (Lemhadri, et al., 2004). The results on the normal rats demonstrated a slight decrease after both single dose and 15 daily doses. On the other hand, results on the STZ rats demonstrated a significant decrease in the blood glucose levels and even reached normal levels after 4 daily doses. They concluded that Origanum vulgare does exhibit anti-hyperglycemic activity in STZ rats.


In 2002, experiments were conducted at the University of Central Florida, Department of Chemistry to determine if compounds in Origanum vulgare can produce antithrombin activity (Goun, et al., 2002). They isolated aristolochic acid I, aristolochic acid II and D-(+)-raffinose from Origanum vulgare and studied the activity of these compounds against leukemia. Both compounds isolated demonstrated high inhibition of thrombin activity and researchers confirmed that the compounds possessed activity against cancer.

Using post-column High Performance Liquid Chromatography or HPLC, the researchers proved the antioxidant properties of herbal drugs including Origanum vulgare (Raudonis, et al., 2009). They identified, which compounds had the highest antiradical activity equivalent in the herb extracts by using standard stable free radicals such as DPPH or 1,1-diphenyl-2-picrylhydrazyl radical and ABTS or 2,2’-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) and the photocolorimetric method to determine the amount of activity of the mentioned compounds. They proved that Origanum vulgare indeed had antioxidant properties and the compounds in it with the highest antiradical activity were Vitexin-2, Rutin, Hyperoside and Rosmarinic acid, which had the highest rating.


At the Department of Biology of the Anadolu University in Turkey, researchers studied the effects of carvacrol on cell morphology, apoptosis and total protein amount of human non-small cell lung cancer cell line A549, which is in approximately 75% of lung cancer incidences (Koparal and Zeytinoglu, 2003). They observed a decrease in the cell number, degeneration of cell morphology and a decrease in total protein amount in the A549 cell line where carvacrol was applied. Observed using a light microscope, the cells treated with carvacrol appeared detached from the disk, more rounded and irregular and with cytoplasmic blebbing. Because of this, they concluded that carvacrol worked well in inhibiting the cell growth at the A549 cell line.


At the Prince Henry Hospital Department of Nephrology in Sydney, Australia, scientists studied the inhibitory effect of Rosmarinic acid, a compound found in oregano oil in the complement-dependent inflammatory processes in both the classical pathway and C3-convertase and cobra venom factor-induced, alternative pathway convertase to understand its mechanism of inhibition (Peake, et al., 1991). They discovered that rosmarinic acid was more effective in instances wherein the terminal attack sequence played a role in pathogenesis.

A study involved evaluating the effects of oregano oil as non-specific immunostimulating agents using growth-retarded, low-weight growing-finishing pigs (Walter & Bilkei, 2004). Researchers observed that the animals treated with Origanum vulgare experienced significantly better average daily gain and feed conversion rate, mortality was higher in the non-treated animals, the proportion of CD4, CD8, MHC class II antigen and non-T/non-B cells in peripheral lymphocytes, as well as the proportion of CD4+ CD8+ double-positive T lymphocytes in peripheral blood and mesenteric lymph nodes were higher in the treated group. In conclusion, supplementation of dietary oregano indeed showed improved growth in growth-retarded growing-finishing pigs and non-specific immunostimulatory effects on porcine immune cells.


Astani A., Reichling J. and Schnitzler P. Comparative study on the antiviral activity of selected monoterpenes derived from essential oils. Phytotherapy Research. 2009 Aug 3.

Force M., Sparks W.S. and Ronzio R.A. Inhibition of enteric parasites by emulsified oil of oregano in vivo. Phytotherapy Research. 2000; 14(3): 213-214.

Goun E., Cunningham G., Solodnikov S., Krasnykch O. and Miles H. Antithrombin activity of some constituents from Origanum vulgare. Fitoterapia. 2002; 73(7-8): 692-694.

Guo N., Liu J., Wu X., Bi X., Meng R., Wang X., Xiang H., Deng X. and Yu L. Antifungal activity of thymol against clinical isolates of fluconazole-sensitive and –resistant Candida albicans. Journal of Medical Microbiology. 2009; 58(Pt 8): 1074-1079.

Hersch-Martinez P., Leaños-Miranda B.E. and Solorzano-Santos F. Antibacterial effects of commercial essential oils over locally prevalent pathogenic strains in Mexico. Fitoterapia. 2005; 76(5): 453-457.

Koparal A.T. and Zeytinoglu M. Effects of Carvacrol on a Human Non-Small Cell Lung Cancer (NSCLC) Cell Line, A549. Cytotechnology. 2003; 43(1-3): 149-54.

Landa P., Kokoska L., Pribylova M., Vanek T. and Marsik P. In vitro anti-inflammatory activity of carvacrol: Inhibitory effect on COX-2 catalyzed prostaglandin E(2) biosynthesis. Archives of Pharmacal Research. 2009; 32(1): 75-78.

Lemhadri A., Zeggwagh N.A., Maghrani M., Jouad H. and Eddouks M. Anti-hyperglycaemic activity of the aqueous extract of Origanum vulgare growing wild in Tafilalet region. Journal of Ethnopharmacology. 2004; 92(2-3): 251-256.

Lopez P., Sanchez C., Batlle R. and Nerin C. Vapor-phase activities of cinnamon, thyme, and oregano oils and key constituents against foodborne microorganisms. Journal of Agriculture and Food Chemistry. 2007; 55(11): 4348-4356.

Osakabe N., Takano H., Sanbongi C., Yasuda A., Yanagisawa R., Inoue K. and Yoshikawa T. Anti-inflammatory and anti-allergic effect of rosmarinic acid (RA); inhibition of seasonal allergic rhinoconjunctivitis (SAR) and its mechanism. BioFactors. 2004; 21(1-4): 127-131.

Peake P.W., Pussell B.A., Martyn P., Timmermans V. and Charlesworth J.A. The inhibitory effect of rosmarinic acid on complement involves the C5 convertase. International Journal of Immunopharmacology. 1991; 13(7): 853-857.

Peñalver P., Huerta B., Borge C., Astorga R., Romero R. and Perea A. Antimicrobial activity of five essential oils against origin strains of the Enterobacteriaceae family. Acta Pathologica, Microbiologica et Immunologica Scandinavica. 2005; 113(1): 1-6.

Raudonis R., Jakstas V., Burdulis, D., Benetis R. and Janulis V. Investigation of individual constituents to antioxidant activity in herbal drugs using postcolumn HPLC method. Medicina (Kaunas). 2009; 45(5): 382-394.

Sanbongi C., Takano H., Osakabe N., Sasa N., Natsume M., Yanagisawa R., Inoue K.I., Sadakane K., Ichinose T. and Yoshikawa T. Rosmarinic acid in perilla extract inhibits allergic inflammation induced by mite allergen, in a mouse model. Clinical and Experimental Allergy. 2004; 34(6): 971-977.

Stamatis G., Kyriazopoulos P., Golegou S., Basayiannis A., Skaltsas S. and Skaltsa H. In vitro anti-Helicobacter pylori activity of Greek herbal medicines. Journal of Ethnopharmacology. 2003; 88(2-3): 175-179.

Walter B.M. and Bilkei G. Immunostimulatory effect of dietary oregano etheric oils on lymphocytes from growth-retarded, low-weight growing-finishing pigs and productivity. Tijdschrift voor Filosofie. 2004; 129(6): 178-181.

Xu J., Zhou F., Ji B.P., Pei R.S. and Xu N. The antibacterial mechanism of carvacrol and thymol against Escherichia coli. Letters in Applied Microbiology. 2008; 47(3): 174-179.