The following information is intended to help people who are allergic to onion, garlic or both.
We believe that true allergy to either of these two foods is very rare in the UK, although no exact figures are available. The Anaphylaxis Campaign membership includes four people who appear on our register as allergic to onion and two who are allergic to garlic (June 2018). In addition, one other person is allergic to both. This is out of a total membership of around 3,700 members.
If you suffer unpleasant symptoms triggered by onion or garlic, it is possible there is a cause other than allergy. This is covered below under the heading “Food intolerance.”
True food allergy
This occurs when the body’s immune system mistakenly identifies a particular food as a threat and releases chemicals such as histamine in response. It is the release of these chemicals that causes the allergic symptoms.
The symptoms of a true food allergy can come on rapidly. These may include nettle rash (otherwise known as hives or urticaria) anywhere on the body, or a tingling or itchy feeling in the mouth.
If you believe you are allergic to a food, this should be reported to your GP, who can refer you to an allergy clinic for testing if necessary. If the tests prove negative, the allergist may consider that your symptoms have some other cause such as an intolerance.
Once a culprit food has been identified, it is important to be vigilant in order to avoid that food. Some people with food allergy suffer symptoms that are severe – a condition known as anaphylaxis. Although anaphylaxis to onion and garlic is believed to be very rare indeed we would advise you to discuss with your GP or allergist what symptoms are likely to occur in your case. Any prescribed treatment should be carried with you at all times.
As stated above, we believe that true allergy to either of these two foods is very rare in the UK. For many people, the actual cause of symptoms is a food intolerance. Food intolerance occurs when a person’s gut is abnormally sensitive and reacts to foods that trigger spasms and distend it with gas or fluid. Intolerance to onion or garlic can be a considerable problem for people with irritable bowel syndrome (IBS).
If your problem is thought to be an intolerance rather than an allergy, the treatment will be different. Discuss this with your doctor.
Avoiding onion and garlic
Onion and garlic are used as ingredients in a wide variety of pre-packed foods and in many dishes sold in restaurants, takeaways, hotels etc. Read food ingredient lists carefully every time you shop and when you eat out, question staff directly. Note that both of these foods are common ingredients in Indian and other Oriental foods and also widespread in sauces, chutneys, processed meats, soups etc. If you are in doubt about any pre-packed product contact the manufacturer.
What else might I react to?
If you are allergic to onion, you could find you also react to garlic and vice versa. This is a process known as “cross-reactivity”. Other foods in the same group could also cause a problem including leek, asparagus and chives. Research suggests that the level of cross-reactivity among the different vegetables in this group is likely to vary among individuals. All cases are different, so you would need to discuss this with your allergist.
Further information on anaphylaxis
Click here for information on anaphylaxis.
Reviewer: The content of this fact sheet has been peer-reviewed by Dr Adrian Morris, Principal Allergist at Surrey Allergy Clinic Guildford and London; and Honorary Clinical Assistant, Allergy and Respiratory Clinic, Royal Brompton Hospital. He reports no conflicts of interest in respect of his review of this article.
References: All the information we produce is evidence based or follows expert opinion and is checked by our expert Clinical and research reviewers. If you wish to know the sources we used in producing any of our information products, please let us know, when we will gladly supply details.
Disclaimer: The information provided in this article is given in good faith. Every effort has been taken to ensure accuracy. All patients are different, and specific cases need specific advice. There is no substitute for good medical advice provided by a medical professional.