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Adulteration of Oregano Herb and Essential Oil

By Ezra Bejar, PhD
American Botanical Council, PO Box 144345, Austin, TX 78714
Correspondence: email

Citation (JAMA style): Bejar E. Adulteration of oregano herb, and essential oil of oregano. Botanical Adulterants Prevention Bulletin. Austin, TX: ABC-AHP-NCNPR Botanical Adulterants Prevention Program; 2019.

Keywords: Adulteration, essential oil, Lippia graveolens, Mediterranean oregano, Mexican oregano, oregano, oregano leaf oil, Origanum onites, Origanum vulgare subsp. hirtum

Goal: The goal of this bulletin is to provide timely information and/or updates on issues of intentional and accidental adulteration and mislabeling of oregano herb and essential oil (EO).* It provides information on issues of adulteration and mislabeling of oregano (Origanum vulgare subsp. hirtum, O. onites) herb used as a spice and herbal remedy, in particular with winter savory (Satureja montana, Lamiaceae) herb, sweet marjoram (Origanum majorana, Lamiaceae) herb, Cistus spp. (Cistaceae) leaf, olive (Olea europaea, Oleaceae) leaf, thyme (Thymus spp., Lamiaceae) herb, summer savory (Satureja hortensis, Lamiaceae) herb, strawberry (Fragaria spp., Rosaceae) leaf, sumac (Rhus spp., Anacardiaceae) leaf, hazelnut (Corylus avellana, Betulaceae) leaf, myrtle (Myrtus communis, Myrtaceae) leaf, and colored wheat (Triticum aestivum, Poaceae) bran. Additional species in the family Lamiaceae from the genera Origanum, Thymus, Poliomintha, Plectranthus, Monarda, and Hyptis or in the family Verbenaceae from the genera Lippia, Aloysia, and Lantana are known to have “oregano” as part of their common name, and may thus be mistaken for oregano by purchasing personnel who lack proper training.

The bulletin also addresses adulteration of oregano (Origanum vulgare subsp. hirtum) EO, in particular with Origanum and Thymus species, Spanish thyme blend, and synthetic carvacrol and thymol. This bulletin may serve as guidance for quality control personnel, the international herbal products industry and the extended natural products community in general. It is also intended to present a summary of the scientific data and methods on the occurrence of species substitution, adulteration, the market situation, and economic and safety consequences for the consumer and the industry.

1          General Information

1.1 Common name: Oregano^1,2†

1.2 Other common names^2-5

Greek oregano:

English: Wild marjoram
Danish: Almindelig merian, merianurt
Dutch: Oregano, wilde marjolein
French: Origan, origan commun
German: Dostenkraut, gemeiner Dost, Oregano, wilder Majoran
Greek: Ρίγανη (rigani)
Italian: Maggiorana selvática, origano, origano comune,
Norwegian: Bergmynte, oregano
Portuguese: Orégano, orégão
Spanish: Orégano
Swedish: Kungsmynta, oregano
Turkish: Kekik, Keklik otu

Turkish oregano:

English: Cretan oregano, Oikea oregano, pot marjoram
Danish: Fransk merian, Tyrkisk merian, pottemerian
Dutch: Potmarjolein, Kretenzische oregano, Turkse oregano
French: Origan de Chypre, origan crêtois, origan turc
German: Französischer Majoran, Kretischer Dost, Kretischer Oregano, Türkischer Oregano
Greek: Τούρκικη ρίγανη (Tourkiki rigani)
Italian: Origano siciliano, origano cretico
Norwegian: Fransk merian
Portuguese: Orégano turco
Spanish: Orégano cretense, orégano italiano, orégano, orégano turco
Swedish: Smyrnamejram, spansk timjan, spansk dosta, fransk mejram, krukmejram
Turkish: Bilyali kekik, Izmir kekiği

1.3 Accepted Latin binomials:

2.2 Market dynamics: 

In 2011, high quality dried oregano (min. 2.5% EO content) of Turkish origin was sold at wholesale prices of US $2.58/kg while material of lower quality was available at US $1.58/kg. In the same year, oregano (Origanum vulgare) from Peru was priced at US $3.20/kg and Mexican oregano (Lippia spp.) originating in Mexico at US $5.51/kg.⁴⁰ Prices of dried Turkish oregano in 2016 were US $4.30/kg in the US and US $4.56 in Europe,⁵⁰ while Mexican oregano was sold by wildcrafters at a fraction of a dollar (8-10 pesos/kg) and at US $5.00/kg (100 pesos) by suppliers.⁵¹

An informal investigation of the retail prices for “oregano” essential oil from Chinese distributors (depending on amount purchased and if whole herb or leaf) on Alibaba.com showed products sold for as low as US $1/kg, although starting prices were more often in the US $10-25/kg range, which is well below the normal price range for authentic oregano oil. Based on information from the International Trade Centre, the price of pure oregano oil from Mediterranean source was in the range of 70-120 €/kg in 2014,^23,50 with corresponding prices in US $ fluctuating between 80-150/kg.

3. Adulteration

3.1 Known adulterants:

3.1.1 Known adulterants of oregano herb

A survey of the European market from 2001 to 2007 revealed products frequently labeled and sold as “true” Mediterranean oregano contained: (1) plants lacking a clearly detectable EO profile, added as bulk extraneous material including berries (Rubus spp., Rosaceae), hoary rockrose (Cistus × incanus, Rosaceae), Sicilian sumac (Rhus coriaria, Anacardiaceae) and, (2) essential oil-bearing plants with oregano-like flavor, mostly belonging to the Lamiaceae family (S. montana and O. majorana).^52,53 Other reports indicate adulteration of oregano leaves may occur with anise (Pimpinella anisum, Apiaceae) seeds, myrtle (Myrtus spp., Myrtaceae) leaves, European hazelnut (Corylus avellana, Betulaceae) leaves, olive (Olea europaea, Oleaceae) leaves, and artificially colored wheat (Triticum aestivum, Poaceae) bran.^{18,37,52,54-56}

Given that the definition of the oregano plant encompasses several species of plants with similar properties, commercial decisions to purchase one or other oregano species has been largely based on availability of raw material, cost, and regional acceptability. There is a clear morphological and organoleptic distinction which can be made between Mediterranean and Mexican oregano for identity purposes using microscopic, macroscopic, and organoleptic methods. However, North American and European market trends are predominantly driven by regional preferences and market acceptability, represented in the U.S. by the American Spice Trade Association (ASTA) and in Europe by the European Spice Association (ESA) with their own definitions and cleanliness specifications (see section 1.6).¹⁸

3.1.2 Known Adulterants of Oregano Essential Oil

Adulteration, such as the use of lower-cost synthetic or natural material added to natural EOs, is a significant problem in the EO industry.⁵⁷ Adulteration of oregano oil occurs with synthetic thymol, carvacrol (or thymol-carvacrol mixtures), or limonene added from different sources.^58,59 Carvacrol can be produced in a synthetic manner using a number of starting materials, e.g., by alkylation of o-cresol.^60,61 “Thyme oil white“ from Spain is a frequent adulterant used to dilute pure EOs. This is a blend made out of several natural fractions of Spanish thyme (Thymus zygis) oil, plus other oregano species (besides O. vulgare) with added natural p-cymene. (E. Schmidt email, November 29, 2017) Spanish thyme oil contains around 40-50% thymol and 4% carvacrol.⁵⁸ Adulteration with EO from Thymus spp., or synthetic thymol has also been found during routine quality control assessments in industry laboratories (C. Beaumont, [dōTerra] oral communication to S. Gafner, February 7, 2019). Synthetic thymol can be obtained in a similar manner as synthetic carvacrol, e.g. using m-cresol as a starting material which is subjected to alkylation with propylene.⁶²

3.2 Sources of information supporting confirmation of adulteration:

3.2.1. Oregano spice

In its guidance document, ASTA reports that oregano adulteration is a common practice. The organization reported the sale of oregano with extraneous matter from different parts of other plants of similar appearance and determined that this is typically added at the cutting/grinding/blending stage.⁶³ Oregano is frequently adulterated with Cistus spp., sumac, and myrtle. The Cistus genus has 20 species – perennial shrubs found on dry or rocky soils throughout the Mediterranean region, from Morocco and Portugal to the Middle East. Cistus leaves have a dark green color that, when added to oregano, makes the adulterated spice visually more appealing than pure oregano.⁶³ Other herbs which have been found in oregano include winter savory and sweet marjoram. Seven commercial Mediterranean oregano samples also exhibited different contamination levels of O. majorana (ranging between 0% and 95%) and S. montana (ranging between 0% and 9.7%). These samples were obtained from wholesale traders during a survey carried out between 2001 and 2009.⁵²

In a more recent report from the United Kingdom, 53 commercially available oregano samples were purchased at various retailers, including convenience shops, supermarkets, and market places in the UK and Ireland.¹⁸ In addition, 25 samples were also purchased from online retailers from EU and non-EU countries. Samples were tested for identity using spectrometric methods (FTIR and LC-HRMS). Approximately 24% of the total 78 oregano samples tested were adulterated and the amount of adulterant ranged from 30% to over 70%; two samples had no oregano present. Similar figures were found for oregano purchased from retail stores and on the Internet. The most common adulterants found in the samples were olive leaves and myrtle leaves. No difference was found between samples purchased in supermarkets and those online.¹⁸

CHOICE, a consumer advocacy group in Australia, had 12 commercial oregano products tested, representing more than 80% of the value of Australia’s oregano sales in the herb and spice product category. Samples were analyzed for authenticity by Fourier transform infrared (FTIR) spectroscopy and subsequent statistical testing. The results gave evidence that seven of these products contained less than 50% oregano and were adulterated with olive leaves or sumac leaves.^64-66 The consumer advocate group referred the issue to the Australian Competition and Consumer Commission.^67,68 Based on the complaint, ACCC initiated its own investigation into a number of oregano brands, and found that one brand manufactured in Australia and three other products sold as oregano leaves were mislabeled since they contained substantial amounts of undeclared olive leaves.^67,68

Finally, in a presentation on the quality control of spices, Larry Lichter, Vice-President of Global Quality and Food Safety at McCormick & Co., Inc., reported that oregano adulteration is common in non-qualified supply chains (i.e., the “spot market”, also known as “cash market”, where commodities are immediately delivered after the sale), with sumac, olive, strawberry, myrtle, hazelnut, and cistus leaves being the principal adulterants.⁶⁹

3.2.2 Oregano oil

In 2014, an alert on the EU RASFF (Rapid Alert System for Food and Feed) portal was placed on a nutritional supplement distributed in the Czech Republic, Germany, Finland, and Slovakia. The oregano oil product in capsules packed in Finland was found to be adulterated with litsea (Litsea cubeba, Lauraceae) oil, a widely used EO in the perfumery and cosmetic industry, but considered to be a potential allergen due to its citral content.⁷⁰

Essential oil expert Erich Schmidt, PhD in his chapter on the adulteration of EOs in the Handbook of Essential Oils, 2nd edition, reports that: “Origanum oil is adulterated with synthetic thymol and carvacrol, or with limonene from different sources.” Adulteration with carvacrol is also mentioned in Hager’s Handbuch der Pharmazeutischen Praxis.¹³

3.3 Accidental or intentional adulteration:  

Both intentional and accidental substitution seems to occur, based on anecdotal and scientific evidence.^18,53 The scenario is complicated by the large heterogeneity of the Origanum genus and by the denomination of different botanical genera under a single generic name. According to ASTA, oregano herb adulteration is economically motivated and intentional.⁶³ Oregano is frequently adulterated with Cistus spp., to intentionally give a dark green color when added to oregano. This makes the adulterated spice more visually appealing than pure oregano. The addition of undeclared plant materials, such as myrtle, olive, sumac, and hazelnut leaves, may be accidental, but in most cases these ingredients are added for financial gain. Adulteration with savory, thyme, or marjoram frequently reported in the literature is likely accidental.

The adulteration of oregano EO appears to be economically motivated. The so-called “thyme oil white” (see section 3.1.2) is available at a lower cost than oregano oil, and therefore admixture of this oil with oregano oil can increase profit for the seller.^58,71

3.4. Frequency of occurrence:

The frequency of adulteration of oregano herb appears to be high. Marieschi et al. found that 61 of the 84 samples (72.6%) obtained from international wholesale traders exporting to the European Union contained more than the permissible 2% of foreign matter, including up to 77% winter savory and up to 95% marjoram. Almost all the samples contained stem parts above the permissible 2% content (stem contents between 1.5-12% were detected).⁵³

Investigations into the composition of commercial oregano spice samples in Argentina found that all samples contained 5% or more of foreign matter. Using macroscopic and microscopic features, colored wheat bran was detected in four out of six (67%),⁵⁶ and 10 out of 36 (28%) samples,⁵⁵ respectively.

Between 30% to over 70% of oregano samples in the UK and Ireland tested were found to include other non-oregano materials, with a follow-up investigation of 54 oregano samples suspected to be adulterated finding that 85% of the products contained 20% or more undeclared bulking agents (cistus, myrtle, olive or sumac leaves).^18,72 An investigation in Denmark found that four out of 10 oregano herb samples contained between 30-50% bulking agents such as cistus and olive leaves.⁷³ Over 50%, or seven out of 12 of the popular brands tested in Australia, also contained substantial amounts of other plant materials.⁶⁴

The frequency of adulteration of oregano oil is not known as the information is scant, but suggestive of widespread adulteration. Erich Schmidt communicated that all of the 38 commercial samples of oregano oil analyzed in his laboratory were adulterated with Spanish white thyme oil and p-cymene. (E. Schmidt, email November 29, 2017).

3.5 Possible safety/therapeutic issues:

According to ASTA, oregano herb is commonly adulterated with non-toxic, less expensive leaves, such as sumac, cistus, or myrtle. This economically motivated adulteration is done with material that does not present a significant public health risk.⁶³

As mentioned above, one of the adulterating materials of oregano oil was found to be Litsea cubeba oil.⁷⁰ This is an EO from a tree widely found in China, Indonesia, and other parts of Southeast Asia that has uses in the fragrance industry. The content of citral in the oil is typically about 70% and is known to be a skin irritant and skin sensitizer.⁷⁴ Cosmetic regulations in the EU require citral, when present above 0.01% in rinse-off products (soaps, shampoos), or above 0.001% in leave-on products (creams, deodorants)), to be declared as an allergenic compound.⁷⁵

3.6 Analytical methods to detect adulteration:

Macroscopic and microscopic methods of analysis for the authentication of oregano herb have recently been reported.^17,53,54,76 Macroscopic identification criteria can be found, e.g., in the monograph of the European Pharmacopoeia,¹⁷ or the publication by Varela et al.⁵⁵ Bononi et al. published microscopy images of oregano, cistus, hazelnut, marjoram, olive, sumac, and savory leaves.⁵⁴ The European Pharmacopoeia also details a thin-layer chromatography (TLC) test which can be used for oregano herb and oregano EO.¹⁷ The extracted oregano herb sample or the corresponding EO are run on a TLC silica gel plate R with methylene chloride as the eluent and anisaldehyde as the reagent. Thymol is characterized visually as a pink zone and carvacrol as a pale violet zone on the TLC plate. A gas chromatography (GC) procedure for oregano EO has also been reported.¹⁷ In addition, ISO provides a method to determine the identity of oregano oil in accordance with ISO standard 11024 (all parts).⁶

Gas chromatography mass spectrometry (GC-MS) and high-performance liquid chromatography mass spectrometry (HPLC-MS) methods to distinguish oregano leaf from olive leaf, one of the most common oregano herb adulterants, have been published by Bononi et al.^77,78 These methods take advantage of the presence of phenolic compounds, e.g., oleuropein in olive leaves, which are absent in oregano. Black et al. developed and fully validated a two-tier approach utilizing FTIR with multivariate statistical analysis and ultra high-performance liquid chromatography high resolution mass spectrometry (UHPLC-HRMS) to screen for and confirm oregano adulteration by other plant materials, such as cistus, hazelnut, myrtle, olive, and sumac.¹⁸ The same FTIR method was used by Wielogorska et al., and compared to a UHPLC-MS/MS method using ions specific for hazelnut, myrtle, olive, and sumac to detect adulteration. The detection limit (LOD) for FT-IR was established to be 10%; LODs for the UHPLC-MS/MS method were below 2%, except for cistus leaves, for which no suitable marker ion was found.⁷²

An unusual approach to detect oregano herb adulteration was published by Drabova et al.⁶⁹ These authors developed a statistical model to predict oregano adulteration based on the GC-MS/MS analysis of 183 pesticides and HPLC-MS/MS of 335 pesticides in 42 authentic and 34 adulterated oregano samples. Using multivariate statistics, a model was constructed with a good prediction ability according to the authors. Pyriproxyfen, cyfluthrin, and cyhalothrin were identified as the most important markers of possible adulteration.⁷⁹

In response to the CHOICE consumer group food alert in the UK and Australia,⁶⁴ Reading Scientific Services, Ltd., used microscopy and subsequent analyses of the constituents by GC-MS. In addition, oregano samples were analyzed with Next Generation Sequencing (NGS) for rapid determination of the DNA sequences of all ingredients in a sample.⁸⁰

Other rapid methods for detection of oregano herb adulterants in crude material are based on developing and successfully implementing test for molecular markers. These methods include the comparison of random amplified polymorphic DNA (RAPD) markers of oregano and Rubus spp., Cistus incanus, and Rhus coriaria added to oregano as bulk extraneous material. Out of 20 random primers tested, 13 produced sequences that allowed discrimination between Origanum spp. and Rubus caesius, R. coriaria, and C. incanus, with a limit of detection of 1%.⁵³

Sequence characterized amplified region (SCAR) markers for Satureja montana, O. majorana, and olive leaf adulterants were also developed from RAPD markers.^52,81,82 The SCAR primers gave rise to specific sequences and subsequent characterization of bands after gel electrophoresis for the detection of oregano adulterating plants at a concentration of 0.5%.^52,81

Volatile adulterants in oregano oil lack the genetic information from the plant and thus cannot be identified with DNA-based methods. The usefulness of GC fingerprints to authenticate oregano EOs is hampered by the high intraspecific variability in the EO composition.^83,84 To detect adulteration of oregano oil with synthetic carvacrol, a GC-stable isotope ratio (SIR)-MS method is used to measure the stable isotopes. Differences in the ²H/¹H ratio (δ²H) between natural carvacrol (δ²H: -272 to -264), and synthetic carvacrol (δ²H: -190 to -225) can be used to determine the presence of undeclared synthetic carvacrol. (E. Schmidt email, November 30, 2017)

4. Conclusions

Adulteration of oregano herb is prevalent, with a number of foreign materials including Origanum spp., Cistus spp., Thymus spp., Satureja spp., sumac, olive, and myrtle leaves frequently detected. The addition of undeclared colored wheat bran in commercial oregano spice products has been reported from Argentina. Confusion and variations in the definition of oregano, and the number of species commercially bearing the same name may result in accidental adulteration by less thoroughly trained wildcrafters. Regional distinctions and guidelines are established by spice trade associations, limiting impurities of extraneous materials to 1-2%.

The prevalence of oregano oil adulteration is just beginning to be understood, and not much information has been confirmed by laboratory tests and reports in the scientific literature. It appears that more affordable EO components and byproducts from EO processing from the fragrance and flavor industries are being mixed with oils derived from Origanum, Thymus, and species from other genera. Although ISO has established a standard for only Mediterranean oregano oil based on the distinct flavor and aroma provided by high carvacrol and low thymol content, the rationale for this decision does not seem to take into consideration the complexity of the oregano herb definition including more than two dozen different plants. Moreover, oregano oil health benefits are very likely shared by several plant species with the common name “oregano” and not exclusively to Mediterranean oregano.²³ The potential lower cost of raw materials may increase the opportunity for adulteration of Mediterranean oregano oil with essential oils, or oil fractions from a large number of other Origanum species and other plants with a similar fragrance profile.

The adulteration of oregano herb with low-cost materials from other plants is not considered a health issue. However, some concerns have been raised with certain adulterants of oregano oil: Allergic reactions may occur in people sensitive to citral when oregano oil contains sufficient amounts of undeclared essential oils with a high concentration of citral.

The ability to sell adulterated oregano at a fraction of the price of high-quality authentic material leads to a substantial market disadvantage for reputable oregano suppliers and manufacturers. It also increases the pressure on these companies to provide ingredients/products at lower cost to stay competitive. Appropriate quality control procedures need to be in place to ensure the authenticity of oregano-based ingredients.

* Some authors differentiate the volatile oil obtained by steam distillation from essential oil. For the purpose of this document, no such distinction has been made.
^† The common name “oregano” is used for both, O. vulgare subsp. hirtum and O. onites. However, Origanum vulgare subsp. hirtum is also known as Greek oregano, while O. onites is commonly referred to as Turkish oregano (see section 1.6).

5. References

1. McGuffin M, Kartesz JT, Leung AY, Tucker AO. Herbs of Commerce. 2nd ed. Silver Spring, MD: American Herbal Products Association; 2000.
2. Herba Origani. WHO Monographs on Medicinal Plants Commonly Used in the Newly Independent States (NIS). Geneva, Switzerland: World Health Organization; 2010:285-297.
3. Origanum vulgare. 2019. https://species.wikimedia.org/wiki/Origanum_vulgare. Accessed March 18, 2019.
4. Liber Herbarum II. 2019. http://www.liberherbarum.net/pn0052.htm. Accessed August 9, 2019.
5. Seidemann J. World Spice Plants: Economic Usage, Botany, Taxonomy. Berlin, Germany: Springer-Verlag; 2005.
6. Essential oil of oregano [Origanum vulgare L. subsp. hirtum (Link) letsw]. ISO 13171:2016. Geneva, Switzerland: International Organization for Standardization (ISO); 2016.
7. The Plant List. Version 1.1. 2013. http://www.theplantlist.org/tpl1.1/record/kew-143884. Accessed August 19, 2019.
8. Tropicos.org. Missouri Botanical Garden; 2019. https://www.tropicos.org/Name/50104128. Accessed March 18, 2019.
9. The Plant List. Version 1.1. 2013. http://www.theplantlist.org/tpl1.1/record/kew-143959. Accessed August 9, 2019.
10. Medicinal Plant Name Database. Royal Botanical Gardens, Kew. https://mpns.science.kew.org/mpns-portal/plantDetail?plantId=143959&query=Origanum+vulgare&filter=&fuzzy=false&nameType=all&dbs=wcs. Accessed March 18, 2019.
11. García-Pérez E, Fernando Francisco C-Á, Gutiérrez-Uribe JA, García-Lara S. Revisión de la producción, composición fitoquímica y propiedades nutracéuticas del orégano Mexicano. Rev Mex Cienc Agric. 2012;3:339-353.
12. Khan IA, Abourashed EA. Leung's Encyclopedia of Common Natural Ingredients: Used in Food, Drugs and Cosmetics, 3rd ed. Hoboken, NJ: John Wiley & Sons; 2010.
13. Stahl-Biskup E. Origanum. In: Hänsel R, Keller K, Rimpler H, Schneider G, eds. Hagers Handbuch der Pharmazeutischen Praxis, Band 5. Drogen E-O. Berlin & Heidelberg, Germany: Springer-Verlag:949-966.
14. Teuscher E. Oregano. In: Teuscher E, ed. Medicinal Spices. Stuttgart, Germany: Medpharm Scientific Publishers; 2006:268-271.
15. Başer KHC. Biological and pharmacological activities of carvacrol and carvacrol bearing essential oils. Curr Pharm Design. 2008;14(29):3106-3119.
16. Shen D, Pan M-H, Wu Q-L, et al. LC-MS method for the simultaneous quantitation of the anti-inflammatory constituents in oregano (Origanum species). J Agric Food Chem. 2010;58(12):7119-7125.
17. Origani herba. European Pharmacopoeia (EP 9.0). Strasbourg, France: European Directorate for the Quality of Medicines and Health Care; 2014:1464-1465.
18. Black C, Haughey SA, Chevallier OP, Galvin-King P, Elliott CT. A comprehensive strategy to detect the fraudulent adulteration of herbs: The oregano approach. Food Chem. 2016;210:551-557.
19. Codex Committee on Spices and Culinary Herbs. Report of the 4th session of the Codex Committee on Spices and Culinary Herbs. Geneva, Switzerland: Joint FAO/WHO Food Standards Programme Codex Alimentarius Commission;2019.
20. Baričevič D, Bartol T. The biological/pharmacological activity of the Origanum genus. In: Kintzios SE, ed. Oregano: The Genera Origanum and Lippia. London, United Kingdom: Taylor & Francis; 2002:175-213.
21. Mith H, Duré R, Delcenserie V, Zhiri A, Daube G, Clinquart A. Antimicrobial activities of commercial essential oils and their components against food-borne pathogens and food spoilage bacteria. Food Sci Nutr. 2014;2(4):403-416.
22. Tisserand R, Young R. Essential Oil Safety. 2nd ed. London, United Kingdom: Churchill Livingstone Elsevier; 2014.
23. Country Study: an Update on Essential Oil Production in Turkey. Geneva, Switzerland: International Trade Centre;2014.
24. Plants of the World Online. Royal Botanical Gardens, Kew. http://www.plantsoftheworldonline.org/taxon/urn:lsid:ipni.org:names:453395-1. Accessed March 18, 2019.
25. National Resources Conservation Services Plants Database. United States Department of Agriculture. https://plants.usda.gov/core/profile?symbol=ORVU. Accessed March 19, 2019.
26. Germplasm Resources Information Network (GRIN-Taxonomy). United States Department of Agriculture, Agricultural Research Service, National Plant Germplasm System. https://npgsweb.ars-grin.gov/gringlobal/taxonomydetail.aspx?id=448727. Accessed March 19, 2019.
27. D’Antuono LF, Galletti GC, Bocchini P. Variability of essential oil content and composition of Origanum vulgare L. Populations from a north Mediterranean area (Liguria region, northern Italy). Ann Bot. 2000;86(3):471-478.
28. Vokou D, Kokkini S, Bessière JM. Origanum onites (Lamiaceae) in Greece: Distribution, volatile oil yield, and composition. Econ Bot. 1988;42(3):407-412.
29. Arabacı O, Bayram E, Tan U, Sönmez Ç. Determination of yield and quality properties of selected Istanbul oregano populations (Origanum vulgare subsp. hirtum (Link) Iestwaart). Paper presented at: 27th International Scientific-Expert Congress of Agriculture and Food Industry.2016; Bursa, Turkey.
30. Putievsky E, Dudai N, Ravid U. Cultivation, selection and conservation of oregano species in Israel. Paper presented at: Promoting the conservation and use of underutilized and neglected crops. 14. Oregano.1997; Valenzano (Bari), Italy.
31. Kokkini S, Vokou D. Carvacrol-rich plants in Greece. Flav Fragr J. 1989;4(1):1-7.
32. Russo M, Galletti GC, Bocchini P, Carnacini A. Essential oil chemical composition of wild populations of Italian oregano spice (Origanum vulgare ssp. hirtum (Link) Ietswaart):  A preliminary evaluation of their use in chemotaxonomy by cluster analysis. 1. Inflorescences. J Agric Food Chem. 1998;46(9):3741-3746.
33. Singletary K. Oregano: Overview of the literature on health benefits. Nutr Today. 2010;45(3):129-138.
34. Blumenthal M, Busse WR, Goldberg A, Gruenwald J, Hall T, Riggins CW, Rister RS, eds. Klein S, Rister RS, trans. The Complete German Commission E. Monographs—Therapeutic Guide to Herbal Medicines. Austin, TX & Boston, MA: American Botanical Council & Integrative Medicine Communication; 1998.
35. Bruneton J. Pharmacognosy, Phytochemistry, Medicinal Plants. 2nd ed. Hampshire, United Kingdom: Intercept Ltd; 1999.
36. Chishti S, Kaloo ZA, Sultan P. Medicinal importance of genus Origanum: A review. J Pharm Pharmacog 2013;5(10):170-177.
37. Başer KHC. The Turkish Origanum species. In: Kintzios SE, ed. Oregano. The Genera Origanum and Lippia. London, United Kingdom: Taylor and Francis; 2002:109-116.
38. Stahl-Biskup E, Loew D. Origani herba. In: Blaschek W, ed. Wichtl – Teedrogen und Phytopharmaka. Stuttgart, Germany: Wisschenschaftliche Verlagsgesellschaft mbH; 2016:463-464.
39. Clemenson S. Herbs and spices. In: Swainson M, ed. Swainson's Handbook of Technical and Quality Management for the Food Manufacturing Sector. Duxford, United Kingdom: Woodhead Publishing; 2018:433-456.
40. Trumpy S. Herbs market report 2012. 11th World Spice Congress; 2012; Pune, India.
41. Proposed draft standard on dried oregano. Rome, Italy: Joint FAO/WHO Food Standards Programme Codex Committee on Spices and Culinary Herbs; 2019.
42. Revision of the classification of food and feed: Class A: Primary food commodities of plant origin. Rome, Italy: Joint FAO/WHO Food Standards Programme Codex Committee on Pesticide Residues; 2018.
43. Delegación SADER San Luis Potosí. Crea INIFAP nueva tecnología para la producción de orégano resistente a fenómenos climáticos. Vol 2019. Mexico City, Mexico: gob.mx; 2013.
44. Anonymous. Produce Chihuahua mil toneladas de orégano al año. El Diario de Chihuahua [online].2016.
45. Cid-Pérez TS, Nevárez-Moorillón GV, Torres-Muñoz JV, Palou E, López-Malo A. Mexican oregano (Lippia berlandieri and Poliomintha longiflora) oils. In: Preedy V, ed. Essential Oils in Food Preservation, Flavor and Safety. New York, NY: Academic Press; 2016:551-560.
46. Smith T, Kawa K, Eckl V, Morton C, Stredney R. Herbal supplement sales in US increase 8.5% in 2017, topping $8 billion. HerbalGram. 2018;119:62-71.
47. Smith T, Kawa K, Eckl V. Herbal supplement sales in US increase 7.7% in 2016. HerbalGram. 2017;115:56-65.
48. Smith T, Kawa K, Eckl V, Johnson J. Sales of herbal dietary supplement sales in US increased 7.5% in 2015. HerbalGram. 2016;111:67-73.
49. Smith T, Gillespie M, Eckl V, Knepper J, Reynolds CM. Herbal supplement sales in US increase by 9.4% in 2018. HerbalGram. 2019;123:62-73.
50. Market Insider: Spices. Geneva, Switzerland: International Trade Centre;2015.
51. Leon I. Productores de orégano ganan 10% de su precio. El Financiero [online].2014.
52. Marieschi M, Torelli A, Bianchi A, Bruni R. Detecting Satureja montana L. and Origanum majorana L. by means of SCAR–PCR in commercial samples of Mediterranean oregano. Food Control. 2011;22(3):542-548.
53. Marieschi M, Torelli A, Poli F, Sacchetti G, Bruni R. RAPD-based method for the quality control of Mediterranean oregano and its contribution to pharmacognostic techniques. J Agric Food Chem. 2009;57(5):1835-1840.
54. Bononi M, Fiordaliso I, Tateo F. Impiego della tecnica di stereo-microscopia per l’identificazione di foglie di Olea europaea L. in origano contuso. Ingredienti Alimentari. 2010;9(50):6-10.
55. Varela BG, Bosco P, Ganopol MJ, Agostinelli L, Gurni AA. Morpho-anatomical analysis for the quality evaluation in “oregano” commercial samples of Buenos Aires City (Argentina). Bol Latinoam Caribe Plant Med Aromatic. 2014;13(1):20-30.
56. Varela BG, Ganopol MJ, Bosco P, Agostinelli L, Gurni AA. Presencia de salvado de cereal en oréganos comercializados en la ciudad de Buenos Aires (Argentina). Bol Latinoam Caribe Plant Med Aromatic. 2009;8(4):305-307.
57. Casabianca H, Graff JB, Guillamet S. Analyses chirales et isotopiques des principaux constituants de roses et de géraniums. Rivista Italiana Eppos. 1996;Numero Speciale:244-261.
58. de Groot AC, Schmidt E. Essential Oils: Contact Allergy and Chemical Composition. Boca Raton, FL: CRC Press; 2016.
59. Burbank T. The adulteration of essential oils – and the consequences to aromatherapy & natural perfumery practice. International Federation of Aromatherapists Annual General Meeting; 2003; London, United Kingdom.
60. Suntres ZE, Coccimiglio J, Alipour M. The bioactivity and toxicological actions of carvacrol. Crit Rev Food Sci Nutr. 2015;55(3):304-318.
61. Yadav GD, Kamble SB. Synthesis of carvacrol by Friedel–Crafts alkylation of o-cresol with isopropanol using superacidic catalyst UDCaT-5. J Chem Technol Biotechnol. 2009;84(10):1499-1508.
62. Stroh R, Heydel R, Hahn W. Alkylation of phenols with alkenes. In: Foerst W, ed. Newer Methods of Preparative Organic Chemistry. Vol 2. New York, NY: Academic Press; 1963:337-364.
63. Identification and prevention of adulteration. Guidance from the American Spice Trade Association. Washington, DC: American Spice Trade Association; 2016:1-23.
64. Does your spice rack contain fake oregano? [press release]. Marrickville, NSW, Australia: CHOICE April 5 2016.
65. Gafner S. Aldi and Monde Nissin pledge to regularly test oregano spice products after ACCC investigation shows substantial adulteration with olive leaf. Botanical Adulterants Monitor. 2016;9.
66. Han E. Food fraud: Popular oregano brands selling adulterated products. The Sydney Morning Herald [online].2016.
67. ACCC Acts on ‘Oregano’ Misrepresentations [press release number MR 210/16] [press release]. Canberra, ACT, Australia: Australian Competition and Consumer Commission (ACCC), November 9 2016.
68. ACCC takes action on fake oregano [press release]. Marrickville, NSW, Australia: CHOICE, November 9, 2016.
69. Lichter L. McCormick Spice. USP Workshop on Adulteration & Fraud in Food Ingredients and Dietary Supplements; 2018; Rockville, MD.
70. Alert Number - 2014.1743. Undeclared citral (Litsea cubeba oil) in oregano oil capsules from Germany, packaged in Finland. European Commission; 2014. https://webgate.ec.europa.eu/rasff-window/portal/?event=notificationDetail&NOTIF_REFERENCE=2014.1743. Accessed March 21, 2019.
71. Schmidt E. Adulterations of essential oils In: Başer KHC, Buchbauer G, eds. Handbook of Essential Oils: Science, Technology, and Applications. 2nd ed. Boca Raton, FL: CRC Press; 2015:707-746.
72. Wielogorska E, Chevallier O, Black C, et al. Development of a comprehensive analytical platform for the detection and quantitation of food fraud using a biomarker approach. The oregano adulteration case study. Food Chem. 2018;239:32-39.
73. Whitworth JJ. 40% of oregano was adulterated – Forbrugerrådet tænk. Food Navigator [online] 2017.
74. Citral. National Library of Medicine (NLM); 2007. https://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+993. Accessed June 14, 2019.
75. European Parliament: Council of the European Union. Regulation (EC) No 1223/2009 of the European Parliament and the Council of 30 November 2009 on cosmetic products. Brussels, Belgium: European Union; 2009.
76. Di Curzio Srl. L’Origano ed i suoi adulteranti al microscopio. 2017.
77. Bononi M, Fiordaliso I, Tateo F. Rapid GC/MS test for identification of Olea europaea L. leaves in ground oregano. Ital J Food Sci. 2010;22:479-483.
78. Bononi M, Tateo F. LC/MS/MS-ESI (–) identification of oleuropein as marker of Olea europaea L. leaves used as a bulking agent in ground oregano and sage. Ital J Food Sci. 2011;23:145-151.
79. Drabova L, Alvarez-Rivera G, Suchanova M, et al. Food fraud in oregano: Pesticide residues as adulteration markers. Food Chem. 2019;276:726-734.
80. Pendrous R. RSSL offers test for adulterated oregano. Food manufacture [online].2015.
81. Marieschi M, Torelli A, Bianchi A, Bruni R. Development of a SCAR marker for the identification of Olea europaea L.: A newly detected adulterant in commercial Mediterranean oregano. Food Chem. 2011;126(2):705-709.
82. Marieschi M, Torelli A, Poli F, Bianchi A, Bruni R. Quality control of commercial Mediterranean oregano: Development of SCAR markers for the detection of the adulterants Cistus incanus L., Rubus caesius L. and Rhus coriaria L. Food Control. 2010;21(7):998-1003.
83. Baranska M, Schulz H, Krüger H, Quilitzsch R. Chemotaxonomy of aromatic plants of the genus Origanum via vibrational spectroscopy. Anal Bioanal Chem. 2005;381(6):1241-1247.
84. Azizi A, Hadian J, Gholami M, Friedt W, Honermeier B. Correlations between genetic, morphological, and chemical diversities in a germplasm collection of the medicinal plant Origanum vulgare L. Chem Biodiv. 2012;9(12):2784-2801.