A food allergy is an adverse response to the proteins in certain foods. The body's immune system mistakenly identifies these proteins as harmful and reacts by producing antibodies: compounds that fights against the problem substance. This in turn makes the body release chemicals such as histamine, which cause allergic symptoms, like runny eyes and nose, vomiting and skin rashes.
Food allergies present themselves in many ways, but the most common symptoms in children are:
- severe gut symptoms
- very rarely, sudden collapse
- there may also be swelling of the throat and mouth, which can cause difficulty swallowing or speaking
Types of food allergy reactions
Allergic reactions to food can be broadly divided into three categories:
- Immediate reaction (IgE)
- Delayed response (Non-IgE)
- Anaphylactic shock
Your child may not always react in the same way to a particular allergen: for example, milk, egg and peanuts can cause either an immediate or a delayed response.
Immediate reaction (IgE): the allergic symptoms develop quickly, usually within an hour of eating the trigger food. The symptoms vary in severity from skin rashes to life-threatening anaphylaxis. If you or your partner has a history of allergies, asthma, eczema or hay fever, your child may be more likely to develop an allergy, although this doesn't always follow. It may be that your little one has had this food before without any untoward effect, but sometimes allergic reactions occur the second time your little one comes into contact with an allergen. These often take parents by surprise, as your child hasn't reacted when he's first eaten the trigger food. The reaction is usually localised – in a small area such as around the lips or on the face.
Delayed response (Non-IgE): these are harder to recognise because the symptoms don't emerge until hours or even days after your child eats the trigger food. The symptoms may form part of a persistent condition, such as eczema and constipation, but the severity is directly related to how much of the trigger food your child eats.
If you think your child has had an allergic reaction to a food, make an appointment to see your GP at the earliest opportunity. He will give you guidance on the most appropriate course of action, which might include allergy testing or elimination diets.
This is the most extreme allergic reaction – and the one that most parents worry about – is anaphylaxis. A type I reaction, anaphylaxis is an extreme and severe allergic response. It happens when your child’s immune system overreacts to an allergen by producing huge amounts of histamine and other chemicals, which can cause the body to go into shock.
The whole body is affected, often within minutes of exposure, and the symptoms can be life-threatening. The main signs of anaphylaxis are wheezing and breathing problems but other symptoms include:
- Hives and swelling of the skin, lips or face
- Rapid pulse
- Dizziness, fainting, loss of consciousness
- Nausea, vomiting, abdominal cramps, diarrhoea
- Extremely pale skin
Anaphylaxis can be triggered by eating even a tiny amount of a problem food – or, in extreme cases, just by touching that food – and requires immediate medical attention.
Anaphylaxis in children is most commonly triggered by peanuts, other nuts, sesame, milk, fish and eggs. A recent study of children who had suffered an anaphylactic episode found that milk and wheat were the most common triggers. Non-food substances, including antibiotics, bee and wasp stings and latex, can also cause anaphylaxis, although this is less common.
Anaphylactic reactions in children are relatively rare and rarely fatal. The risk of an attack is higher if your child has had a serious reaction before, or if he suffers from asthma as well as an allergy. For more information about anaphylaxis, visit the Anaphylaxis Campaign. If you suspect an anaphylactic reaction, call 999 immediately.
Another less common food allergy is coeliac disease – an allergic reaction to gluten. Gluten is found in wheat, rye, oats and barley, which are often used to make foods such as bread, pasta and biscuits. Exposure to foods containing gluten causes damage to the small intestine and interferes with the normal absorption of food.
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In children, coeliac disease may develop soon after your child first eats gluten. The most obvious symptom is loose, pale stools. Children with coeliac disease may 'fail to thrive' (grow and gain weight too slowly) and tend to be irritable and unhappy. For information and support, contact Coeliac UK.