Oregano

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Code: f283
Latin name: Origanum vulgare
Family: Lamiaceae
Common names: Oregano, Oreganum, Wild Marjoram, Greek Oregano
There is a great deal of confusion between Oregano and Marjoram (f274), partly because of their similar appearance, including the square stems, opposing pairs of leaves and whorled flower spikes typical of the Lamiaceae or Mint family.
 
Moreover, the plants are very closely related, and classification that differed in the past still causes confusion. Now the genus name for both plants is Origanum, and Marjorams are considered types of Oregano, of which there are over 50. (The multiplicity of varieties, including crosses, does not help in creating an orderly taxonomy!) Sweet Marjoram (Origanum majorana) is the most familiar Marjoram. But this official clarity does not prevent another type of Marjoram, Pot Marjoram (Origanum onites), from Crete, from being called Cretan Oregano. Even plants outside the genus are marketed as Oregano: Coleus anboinicus in Puerto Rico (part of a traditional Cuban seasoning), Thymus nummularius in Spain, and Lippia graveolens in Mexico. Conversely, Origanum vulgare, or Common Oregano, may be called Wild Marjoram.
 
Herb
A herb, which may result in allergy symptoms in sensitised individuals.

Allergen Exposure

Geographical distribution
Oregano, comprising the species of the genus Origanum, from the Mediterranean region of Europe and Asia, is an extremely variable plant grown since ancient times for ornamental, culinary and medicinal uses. It is a bushy, semi-woody sub-shrub with upright or spreading stems and branches. The plants are 30 to 60 cm in height, with oblong to ovate, somewhat hairy leaves.
 
Oregano is a member of the Lamiaceae or Mint family, which includes familiar culinary herbs: Mint, Basil, Marjoram and Sage. Although Marjoram and Oregano are similar in appearance (see above), Oregano tends to be "leggier" and less compact, whether it grows upright or in a "mound" like Marjoram. Oregano flowers tend to be purplish pink, unlike the mostly white Marjoram flowers, and the leaves are larger (4 cm), brighter green and coarser. Oregano, unlike Marjoram, is generally considered a perennial herb—but O. vulgare, the most important kind, is usually treated as an annual. Finally, the taste and aroma of Oregano leaves is distinctly stronger.
 
Environment
Oregano's pungent, spicy flavour enhances tomato-based sauces, Eggplant, seafood, Pork, Lamb, Chicken, soups, fried vegetables, barbeque sauce, egg and cheese dishes, and stuffings. Oregano is the characteristic Italian herb, indispensable in pasta sauces and pizza. Oregano use is also traditional in Mexican, Greek, North African and Spanish cooking. Though less popular in northern cuisines, it is certainly not unknown to them.
 
The essential oil reaches a maximum of 4% of content. It includes the phenoles carvacrol and thymol (see also Thyme and savory).
 
Oil of Oregano is used in perfume making. Medicinal uses include pain relief and the treatment of digestive complaints.

Unexpected exposure

See under Environment.
 
Allergens
No allergens from this plant have yet been characterised.

Potential Cross-Reactivity

An extensive cross-reactivity among the different individual species of the genus could be expected, in particular between Oregano and Marjoram (1).

Clinical Experience

IgE-mediated reactions
Oregano may uncommonly induce symptoms of food allergy in sensitised individuals.
 
A 45-year-old man experienced 3 reactions to food: as a result of Oregano on a single occasion, and twice to Thyme. He had pruritis and swelling of the lips and tongue, dysphagia, dysphonia, and progressive upper respiratory difficulty, as well as intense facial and palpebral oedema. On 2 occasions he also had hypotension, vomiting, and nausea. Onset was within minutes after the ingestion of pizza containing the herb in the first instance, meat seasoned with Thyme in the second, and snails with Thyme in the third (2).
 
A 45-year-old female patient, with facial eczema that appeared 20 minutes after ingestion of Oregano and was exacerbated by sun exposure, was reported. A patch test was positive. Three other patients were reported to be positive to Oregano on a patch test, but their symptoms were not described (3).
 
Compiled by Dr Harris Steinman, harris@zingsolutions.com

References

  1. Yman L. Botanical relations and immunological cross-reactions in pollen allergy. 2nd ed. Pharmacia Diagnostics AB. Uppsala. Sweden. 1982: ISBN 91-970475-09
  2. Benito M, Jorro G, Morales C, Pelaez A, Fernandez A. Labiatae allergy: systemic reactions due to ingestion of oregano and thyme. Ann Allergy 1996;76(5):416-8
  3. Futrell JM, Rietschel RL. Spice allergy evaluated by results of patch tests. Cutis 1993;52(5):288-290

 

As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.