Onion allergy
Onion allergy or intolerance.
About onion allergy
Onion is a bulb vegetable in the Allium family, closely related to garlic, leek and chives, and used almost everywhere in cooking. True IgE-mediated onion allergy is uncommon; far more people experience a non-allergic intolerance, digestive upset from the fermentable fibres (FODMAPs) onions contain, or irritation and tears when chopping raw onion. Where genuine allergy exists, the immune system makes antibodies to onion proteins that trigger histamine release on exposure, and some sensitisation is linked to pollen.
When an allergic reaction occurs it usually starts within minutes to a couple of hours of eating. Symptoms may include an itchy or tingling mouth, hives, swelling, a runny nose or digestive upset; serious reactions are rare but not impossible. Intolerance, by contrast, tends to cause bloating, wind and abdominal discomfort some hours after eating, without the skin or breathing features of allergy. Handling raw onion can also cause localised skin or eye irritation. There can be overlap within the onion and garlic family.
Diagnosis rests on your history, supported where useful by skin-prick or specific-IgE testing, since allergy and intolerance can look similar and are managed differently. Management means avoiding onion in fresh, dried and powdered forms and reading labels, as onion is a very common ingredient in stocks, sauces, gravies and processed foods. Most reactions are mild, but if you ever develop widespread swelling, wheeze or faintness, treat it as an emergency and call 999 in the UK.
Common triggers
- Onion and products containing it
Symptoms
- Itching or tingling in the mouth
- Hives, itching or eczema
- Swelling of the lips, face, tongue or throat
- Stomach cramps, nausea, vomiting or diarrhoea
- Wheezing or trouble breathing
- In severe cases, anaphylaxis
Avoidance & management
- Read ingredient labels every time
- Ask about ingredients and cross-contamination when eating out
- Keep the food out of shared cooking areas
- Carry prescribed antihistamines or an adrenaline auto-injector
- Seek emergency help for any severe reaction
Sources & references
Allergy safety: what everyone should know
Mild-to-moderate reaction signs
- Itching, hives or a raised rash
- Swelling of lips, face or eyes
- Tingling mouth, sneezing, runny nose
- Stomach pain, nausea or vomiting
Anaphylaxis — call 999 (UK) or 112 (EU) immediately
- Difficult or noisy breathing, wheeze, persistent cough
- Swelling of the tongue or tightness in the throat
- Dizziness, collapse, pale and floppy (young children)
- Use an adrenaline auto-injector (e.g. EpiPen) at once if prescribed, then call an ambulance even if symptoms improve
Allergy or intolerance? A true allergy involves the immune system and can escalate quickly; an intolerance (e.g. lactose intolerance) is unpleasant but not life-threatening. The symptoms overlap, so self-diagnosis is unreliable.
Getting tested: home-testing kits based on IgG are not diagnostically valid. If you suspect an allergy, ask a GP for referral to an allergy clinic for skin-prick or specific-IgE testing and a supervised food challenge where appropriate.