Soy allergy
Soybean allergy, common in infants and in processed foods.
About soy allergy
Soy, or soya, is a legume used extensively in processed foods, from tofu and soy sauce to emulsifiers, protein isolates and vegetable oils. Allergy to it is common in infants and young children, often alongside cow's milk allergy, and many outgrow it during childhood. The reaction is usually IgE-mediated, with the immune system producing antibodies to soy proteins that trigger a rapid release of histamine and other chemicals, though soy can also cause delayed, non-IgE reactions in some infants.
Symptoms of immediate allergy generally appear within minutes and can include an itchy mouth, hives, swelling, vomiting, wheeze and, in some cases, anaphylaxis. Reactions are often mild, but severe ones do occur, particularly in people who also have asthma or peanut allergy, since soy and peanut are both legumes and share some proteins. People with birch-pollen allergy can also experience mild mouth symptoms from certain soy foods because of a pollen-related protein.
Diagnosis uses the history alongside skin-prick or specific-IgE testing, and sometimes a supervised challenge. Management means avoiding soy and reading labels carefully, as it appears in many manufactured foods, though highly refined soybean oil and lecithin are often tolerated. People at risk of severe reactions carry an adrenaline auto-injector. A severe reaction is a medical emergency needing adrenaline and a 999 call.
Common triggers
- Soybeans, tofu and edamame\nSoy sauce and miso\nSoy lecithin in processed foods
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.