We believe that true allergy to either of these two foods is very rare in the UK, although no exact figures are available.
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”.
This occurs when the body’s immune system mistakenly identifies a 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 and can occur after eating very small amounts of the food. Symptoms 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 suspect you are allergic to a food, report this to your GP who can refer you to an allergy clinic for testing if necessary. If the tests prove negative, the allergist may consider whether your symptoms have some other cause, such as an intolerance.
Once a culprit food is identified, it is important to be vigilant to avoid that food. Some people with food allergy suffer symptoms that are severe – a condition known as anaphylaxis. Although anaphylaxis to onion and/or garlic is believed to be very rare, you should ask your doctor or allergy specialist what symptoms are likely to occur in your case. Always carry any prescribed treatment with you.
Read our anaphylaxis factsheet for further information.
For many people, the actual cause of symptoms is a food intolerance. Food intolerance does not involve the immune system and occurs when a person’s gut is abnormally sensitive to foods. This can cause delayed gut symptoms, such as bloating, stomach pain and wind. Food intolerance symptoms typically only occur if you eat a large amount of the food.
Intolerance to onion or garlic can be a considerable problem for people with irritable bowel syndrome (IBS). If your problem is an intolerance rather than an allergy, the treatment will be different. Discuss this with your doctor.
For both allergy and intolerance to onion or garlic, the degree of cooking may change the likelihood and severity of a reaction. Discuss this with your doctor or allergy specialist.
Onion and garlic are used as ingredients in a wide variety of pre-packed foods and in many dishes sold in restaurants and takeaways. Read food ingredient lists every time you shop and, when you eat out, question staff directly. Both these foods are common ingredients in Indian and other Oriental foods and are also widespread in sauces, chutneys, processed meats, soups etc. If you are in doubt about any pre-packed product, contact the manufacturer.
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” – where the proteins in one food are similar to the proteins in another food. Other foods in the same group could also cause a problem, including leeks, 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 allergy specialist.