Cross-reactivity occurs where the proteins in one food or substance share characteristics with those in another food or substance. A person who is allergic to one may therefore have positive allergy tests to other foods with similar proteins.
Examples would be:
- Some people with peanut allergy can have positive tests to other legumes such as chick peas, kidney beans and green peas. Not everyone with positive tests will actually react to other legumes, although some will.
- Many people who are allergic to the proteins in birch tree and/or grass pollen can also have positive tests to certain plant foods. This is because proteins in fruits, vegetables and nuts are very similar to the pollen proteins. Positive tests to plant foods are common in people with hay fever but they only need to avoid foods which are actually causing symptoms. The allergy to plant foods caused by this cross-reaction is known as pollen food syndrome but can also be called oral allergy syndrome.
- A similar but less common reaction can also occur in people who are allergic to natural rubber latex because some of the proteins present in natural rubber latex also exist in a similar form in certain fruits such as bananas, avocado and chestnuts.
Not everyone with an allergy to foods, pollen or latex will actually react to cross-reacting foods or substances. All cases of allergy require a proper medical diagnosis.
This article has been Peer Reviewed by Dr Michael Radcliffe, Consultant in Allergy Medicine, University College London Hospitals NHS Foundation Trust.
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Published: March 2019
Review date: March 2022