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If someone is allergic to olives, should olive oil also be avoided? Does the oil contain trace proteins from the olive, or just the fat?
Based on an extensive review of the literature, serious allergy to the olive fruit as a food has rarely been reported. There are three case reports of people who reacted to the ingestion of olive fruit, one report describing an allergy to olive fruit developing after pollen allergy shots, and one case of airway disease in an olive oil mill worker.

Skin allergic reactions - such as contact dermatitis or hives - to olive oil have been reported uncommonly.

In contrast, olive trees commonly cause seasonal allergy symptoms from inhaled olive tree pollen, something which typically occurs in specific growing regions.

A little background on the manufacture of olive oil is also in order: olives are cleaned and ground into a paste, which releases the oil, and then the paste is mixed to allow small oil drops to combine into bigger ones. The extracted olive oil is then separated from the fruit water and solids. Given this process, which is considered a "cold press" extraction, it is conceivable that the resulting olive oil could contain olive proteins. However, the infrequent reports of olive fruit or olive oil allergy might be related to the fact that the protein content of an olive itself is very low, approximately 2%. Of the patients reported in the literature having olive fruit food allergy, few were reported to have any reaction to olive oil.

In conclusion: if a person has, via skin tests and/or an oral food challenge, a certain diagnosis of an olive fruit allergy, the likelihood of olive oil allergy is low (due to the very low protein content). However, to be safest, your allergist can perform the same type of diagnostic testing can be done with olive oil.