Onions are in the Amaryllidaceae family of plants which also includes shallots, spring onions (scallions) and leeks. Allergy to onion is very rare, but it can cause allergic contact dermatitis and urticaria.

An allergy to onions after ingestion is more commonly linked to Non-IgE mediated allergy than a true IgE allergy. It is important if you think you are allergic to complete a food diary to ensure you are not eliminating large groups of food unnecessarily. There are tips on how to make a Food Diary here.

One of the allergens identified in onion are Lipid Transfer Proteins (LTP), which are panallergens with the potential to cause allergy over large groups of seemingly unrelated foods.

The other identified allergen is a profilin protein. Again this is a panallergen.

Onions are one of the few fresh foods that contain a moderate amount of naturally occurring sulphites. Sulphites are inorganic salts used in preservations and have the potential to cause symptoms of food intolerance to those sensitive to sulphites, this food intolerance is more common in asthmatics. An improvement in symptoms can be made with a change to a low sulphite diet.

Onions are a high FODMAP food. FODMAP stands for Fermentable oligosaccharides, disaccharides, monosaccharides and polyols. Foods high in FODMAPs can cause symptoms of food intolerance, affecting the gastro intestinal system and this can be mistaken for a true IgE food allergy.

Onions are low in salicylates. Salicylates have the potential to cause gastrointestinal food intolerance symptoms in people who are sensitive to salicylates.

You can read more about Food Intolerances on the dedicated Food Intolerance Page.

An allergy to onion is most often associated with allergic contact dermatitis and urticaria (hives and wheals on the skin), this is due to diallyl disulphide.

If you have allergic symptoms to multiple foods you may be suffering LTP Syndrome.

Allergy to onion can be linked to Celery-Mugwort-Spice Syndrome this is when people are affected by profilin proteins in multiple foods.

Onion is in the Amaryllidaceae plant family, other plants in this family are chives, leeks and garlic. If your allergy is severe these plants may also cause allergic reactions.

Common foods involved in LTP allergy include kiwi, strawberries, sunflower seeds, walnut, apple, mulberry, banana, pea, apricot, cherry, plum, almond, peach pomegranate, raspberry, tomato, grape, celery, peanut, asparagus, cabbage, broccoli, chestnut, lemon, tangerine, orange, hazelnut, lettuce, lentils, lupin, green bean, pear, mustard, wheat and maize.

Profilin proteins are also found in celery, peanut, soyabeans, walnut, lupin, almonds, mustard, hazelnut, kiwi, pineapple, chilli, melon, orange, strawberry, lychee, apple, banana, aubergine (eggplant), peach, pear, tomato, dates, cherry, carrot, barley and wheat.

Please note that these food lists are not exhaustive. The most up to date information is on the Cross Reactivity Tool.

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