Food allergy

Expert review by: Dr Stephanie Kayode, Consultant Allergist

Key points

• A food allergy is when your body’s immune system reacts to certain foods as if they’re harmful.
• Some of the most common food allergies are to cow’s milk, peanuts, egg, tree nuts, soya, fish, and shellfish. Allergies to pine nuts and legumes, such as peas and lentils, are less common.
• Food allergy is diagnosed using skin-prick tests, blood tests, or both.

Common food allergies

Lots of different foods can cause an allergic reaction. These are known as allergenic foods. Some of the most common food allergies include the following.

• Cow’s milk and dairy products (for example, yoghurt and cheese). Children with cow’s milk allergy almost always develop it before the age of one. Most children grow out of it by the time they are adults. If you’re allergic to cow’s milk, you’re more likely to be allergic to goat’s and sheep’s milk too.
• Eggs. Most children will outgrow egg allergy as they get older, with many developing some tolerance by the age of five.
• Peanuts. This usually develops in childhood but can sometimes develop in adults. It’s one of the most common causes of severe allergic reactions.
• Tree nuts, including hazelnuts, Brazil nuts, almonds, cashews, and walnuts. If you’re allergic to one type of tree nut, you may also have an allergy to another. Most children don’t outgrow their nut allergies.
• Wheat. This mainly affects children, but sometimes adults can develop wheat allergy.
• Fish and shellfish. People are often allergic to several different types of fish or shellfish.
• Some raw fruits and vegetables, in people who have hayfever. This can be part of a syndrome called pollen food syndrome or oral allergy syndrome, which is linked to an allergy to tree or grass pollen. It most commonly involves apples and fruits with stones, such as peaches, plums, and cherries. But almost any fruit, vegetables, or nuts can trigger a reaction. Pollen food syndrome tends to cause a mild allergic reaction in your mouth.
• Soya. This usually starts in babies or children and is less common than other food allergies in the UK. Many children outgrow it as they get older.
• Sesame seeds. This usually starts in childhood, and most people continue to be allergic as adults.

Some other allergens, such as pine nuts, peas, and lentils, can also trigger an allergic response. But these are less common.

Causes of food allergy

Food allergies can develop at any age. It’s unclear exactly why some people develop a food allergy, but it’s thought likely to be due to a combination of factors. The following things are known to increase the risk of food allergy.

• Having eczema or skin infections before the age of one.
• Having family members who have food allergies or other allergic conditions.
• Already having one food allergy tends to increase your risk of getting another one.
• Delayed introduction of allergenic foods, such as peanuts. Studies have shown that introducing peanut, egg, or cow’s milk to young infants can reduce their risk of allergies to these foods.

What are the signs of a food allergy?

For most food allergies, symptoms come on very quickly. This is usually within minutes after you’ve eaten or been in contact with the food and almost always within two hours. Just eating a tiny amount of a food allergen, or even breathing it in or touching it may trigger a reaction. You may have some of the following symptoms:

• itchy, red and swollen skin (often around your lips, face or eyes), and a rash
• wheezing, a cough, noisy breathing or shortness of breath
• hoarse voice, throat tightness, or difficulty swallowing
• an itchy or tingling feeling and swelling in your mouth, including your lips and tongue.
• a runny, blocked or itchy nose and sneezing
• diarrhoea, bloating or tummy cramps
• feeling sick or vomiting

These symptoms don’t always mean you have a food allergy. But contact your GP if you do notice symptoms after eating certain foods.

Severe allergic reactions

Food allergies can also cause a severe allergic reaction called anaphylaxis, which affects your whole body. You may have difficulties breathing and circulation problems. You might feel drowsy or pass out (lose consciousness). Anaphylaxis can be life-threatening and you’ll need medical help straight away. If someone is having trouble breathing or is losing consciousness, call 999 immediately.

Diagnosis of food allergy

Your GP will ask you about your symptoms, including how often you’ve had them, how long they last, and how severe they are. They’ll want to know what foods you ate before the reaction, how much you ate, and how quickly your symptoms developed after eating them. It can be helpful to keep a food diary (PDF, 1.4MB) to keep track of this.

Your GP will also ask whether you have any allergy-related conditions, such as eczema or asthma. They’ll also want to know whether anyone in your family has food allergies or other allergy-related conditions.

Food allergy treatment

Your doctor will give you advice on how to recognise symptoms of an allergic reaction if you’re accidentally exposed to a food that affects you. They’ll also tell you how to deal with a reaction, and may suggest or prescribe some medicines you can take. These may include the following.

• Antihistamine tablets. If your allergy is mild, your doctor may suggest these. You should take them as soon as an allergic reaction starts.
• Self-injectable adrenaline. If you have a severe allergic reaction to a food, your doctor may prescribe adrenaline auto-injectors (eg EpiPen or Jext). You can use these to inject yourself (or your child) in an emergency. You’ll be shown how and when to use them. Always carry two auto-injectors with you, in case of emergency.

If you have a severe reaction that affects your airway, breathing, or circulation, you should go to your nearest Accident and Emergency department. You may need hospital treatment. This may involve having adrenaline injections or an infusion in hospital.

Preventing food allergies

There has been much research into how what you eat during pregnancy and what you feed your baby may affect the risk of food allergies. The advice has changed many times during the years.

If you’re pregnant, there’s no need to avoid foods that can trigger allergies. There’s no evidence that this will affect your child’s risk of developing an allergy. There’s some evidence that breastfeeding may help protect against development of allergies, but more studies are needed.

UK guidance currently advises only giving babies solid foods – including foods like eggs, finely ground nuts, and nut butters – from six months of age. Delaying the introduction of these foods can increase the risk of developing an allergy. But early introduction of common food allergens during weaning may reduce the risk of developing an allergy later on.