‘Soya’ or ‘soy’ refers to a food ingredient made from the soya bean, which is a legume. Soya is used to make soy sauce and tofu and is used as an ingredient in many food products.
There are two types of soya allergy: immediate and delayed.
Immediate soya allergy happens when the body’s immune system wrongly identifies soya as a threat and produces a type of antibody known as IgE. When you eat soya, the body releases chemicals, such as histamine, that cause the symptoms.
These reactions tend to happen very soon after eating soya, usually within seconds or minutes, but can sometimes take longer to develop. Very rarely, it can lead to anaphylaxis.
Delayed soya allergy is not very well understood. Although the immune system is probably involved, the IgE antibodies that lead to immediate reactions are not. Symptoms take much longer to come on, and usually appear hours to days after eating soya.
Typical symptoms include stomach pain, vomiting and diarrhoea. This type of allergy doesn’t lead to anaphylaxis and is not life threatening.
Soy can cause symptoms in people with other allergic conditions including Food Protein Induced Enterocolitis Syndrome (FPIES), eosinophilic esophagitis (EoE) and proctocolitis, but these conditions are not covered here.
Mild to moderate symptoms may include:
Most people with soya allergy have mild symptoms but, very rarely, symptoms can be more serious.
The term for this more serious reaction is anaphylaxis (pronounced anna-fill-axis).
Most healthcare professionals consider an allergic reaction to be anaphylaxis when it involves difficulty breathing or affects the heart rhythm or blood pressure. Any one or more of the ABC symptoms above may be present.
In extreme cases there could be a dramatic fall in blood pressure. The person may become weak and floppy and may have a sense of something terrible happening. Any of the ABC symptoms may lead to collapse and loss of consciousness and, on rare occasions, can be fatal.
AIRWAY - swelling in the throat, tongue or upper airways (tightening of the throat, hoarse voice, difficulty swallowing).
BREATHING - sudden onset wheezing, breathing difficulty, noisy breathing.
CIRCULATION - dizziness, feeling faint, sudden sleepiness, tiredness, confusion, pale clammy skin, loss of consciousness. 
Delayed soya allergy usually involves the digestive system and causes symptoms such as:
Sometimes people have atopic dermatitis (a type of eczema) which may also be a symptom of delayed soya allergy.
If you think you may be allergic to soya, see your GP who can refer you to a specialist allergy clinic if needed. They can find a clinic in your area from the British Society for Allergy and Clinical Immunology (BSACI).
It’s important to get a referral even if your symptoms were mild because it can be hard to tell if future allergic reactions could be more serious. It’s also important to know which type of soya allergy you have.
Once you get a referral, the consultant will discuss your medical history and symptoms with you. They might suggest skin prick tests, blood tests, and food challenge tests to help diagnose the allergy and work out how serious it may be.
Some clues that you might be at higher risk of more serious reactions are:
If you have asthma and it is not well controlled, this could make an allergic reaction worse. Make sure you discuss this with your GP or allergy specialist and take any prescribed medicines.
If you have mild allergic symptoms you may be prescribed antihistamine medicine that you take by mouth. If you are at higher risk of anaphylaxis, you may be prescribed adrenaline to use in an emergency.
Adrenaline comes in pre-loaded adrenaline auto-injectors (AAIs) that are designed to be easy to use. Make sure you know how and when to use them. Ask your healthcare professional to show you how to use your specific brand of AAI. You can also find help and training videos on the manufacturer’s website and get a free trainer device to practise with.
You must carry two AAIs with you at all times, as you may need to use a second one if your symptoms don’t improve after five minutes or get worse.
The adrenaline auto-injectors prescribed in the UK are:
EpiPen®
EpiPen® is available in two doses: Adult: 0.3mgs of adrenaline Junior: 0.15 mgs of adrenaline (suitable for children weighing 5kgs – 25kgs / 1 stone 3lbs – 3 stone 13lbs)
Jext®
Jext® is available in two doses: Adult: 300 mcg of adrenaline Junior: 150 mcg of adrenaline (suitable for children weighing 15kgs – 30kgs / 4 – 4.5 stone)
The main treatment for delayed soya allergy is to avoid soya. As this type of allergy does not cause anaphylaxis and is not life-threatening, you won’t need to carry adrenaline auto-injectors.
If you have eczema you may be prescribed treatments for this.
Once you have been diagnosed with a soya allergy, you will need to avoid soya and foods that contain it.
Read the ingredient lists on food packets carefully every time you shop. Soya is included in the list of the top 14 major food allergens in the UK. This means it must be highlighted on ingredients labels, in bold for example.
Read the ingredient list every time you buy a product as manufacturers change their recipes often.
When eating out
Restaurants, cafes, hotels, takeaways and other catering businesses are required by law to provide information on major allergens, including soya. Ask staff directly if the food you’d like to buy contains soya and if there is a risk of cross contamination. Let them know that even small quantities can cause an allergic reaction and don’t be afraid to ask staff to check with the chef.
Edamame beans – these are immature soya beans and can be bought fresh or frozen.
Tofu, also known as soya bean curd – this is a concentrated form of soya used in Asian foods such as stir fries, soups and curries.
Soya flour – often used in baked foods such as bread, cakes and biscuits.
Infant foods – some may contain soya flour.
Vegetable protein – including hydrolysed vegetable protein (HVP) and textured vegetable protein (TVP).
Lecithin (E322) – an emulsifier normally made from unrefined soya oil and occasionally from rapeseed oil. The risk of reaction may be small but speak to your doctor or allergy specialist about whether soya lecithin is safe for you.
Soya sauce – also known as soy sauce, often used in multi-cultural foods and to add a savoury flavour to soups, gravies, stews and sauces.
Medicines – always ask your pharmacist if soya is an ingredient of medicines.
Soya oil is sometimes used in salad dressings, margarines and spreads. Fully refined soya oils are very unlikely to cause allergic reactions in people with soya allergy because the refining process removes the soya protein (the part of the soya which causes the allergic reaction).
It’s more likely that unrefined soya oil would cause allergic reactions as it’s likely to contain small amounts of soya protein.
In the UK, food allergen labelling regulations say the following.
If you react to one member of the legume family, such as soya, it’s possible you could react to another, such as peas, beans or lentils. This is known as “cross-reactivity”, where the proteins in one legume are similar to the proteins in another. This is not common, but discuss it with your doctor or allergy specialist.
Children with soya allergy are often also allergic to peanuts.
Soya-based infant formulas are not suitable for babies less than six months old. After six months, it may be suitable for some children but speak to your GP or allergy specialist first.
In the UK, soya-based infant formula is not generally recommended by healthcare professionals for infants with cow’s milk allergy, as some are also allergic to soya protein.
A small number of people have had reactions that are believed to have been caused by soya-based materials used to stuff pillows. All of them had a history of food-related hay fever and asthma. If you are allergic to soya, check the contents label of your pillows.
Allergy to soya usually starts in early childhood and it’s thought that around half of children will outgrow it by the age of 7. It is important to have regular follow-up appointments with your allergy specialist and, if you believe your child may have outgrown their allergy and have no appointments planned, ask for an appointment.
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