A food allergy is caused by your immune system handling harmless proteins in certain foods as a threat. It releases a number of chemicals, which trigger an allergic reaction.
The immune system protects the body by producing specialised proteins called antibodies.
Antibodies identify potential threats to your body, such as bacteria and viruses. They signal your immune system to release chemicals to kill the threat and prevent the spread of infection.
In the most common type of food allergy, an antibody known as immunoglobulin E (IgE) mistakenly targets a certain protein found in food as a threat. IgE can causeseveral chemicals to be released, the most important being histamine.
Histamine causes most of the typical symptoms that occur during an allergic reaction. For example, histamine:
In most food allergies, the release of histamine is limited to certain parts of the body, such as your mouth, throat or skin.
In Anaphylaxis , the immune system goes into overdrive and releases massive amounts of histamine and many other chemicalsinto your blood. This causes the wide range of symptoms associated with anaphylaxis.
There's another type of food allergy known as a non-IgE-mediated food allergy, caused by different cells in the immune system.
This is much harder to diagnose as there's no test to accurately confirm non-IgE-mediated food allergy.
This type of reaction is largely confined to the skin and digestive system, causing symptoms such as heartburn, indigestion and eczema.
In babies, anon-IgE-mediated food allergy can also cause diarrhoea and reflux, where stomach acid leaks up into the throat.
In children, the foods that most commonly cause an allergic reaction are:
In adults, the foods that most commonly cause an allergic reaction are:
However, any type of food can potentially cause an allergy. Allergic reactions have been reported in association with:
Exactly what causes the immune system to mistake harmless proteins as a threat is unclear. However, a number of risk factors for food allergies have been identified, which are outlined below.
If you have a parent, brother or sister with an allergic conditionsuch as asthma, eczema or a food allergyyou have a slightly higher risk of developing a food allergy. However, you may not develop the same food allergy as your family members.
Children whohave atopic dermatitis (eczema) in early life are more likely to develop a food allergy.
The number of people with food allergies has risen sharply over the past few decades and,although the reason is unclear, other allergic conditions such as atopic dermatitis have also increased.
One theory behind the rise is that a typical child's diet has changed considerably over the last 30 to 40 years.
Another theory is that children are increasingly growing up in "germ-free" environments. This means their immune systems may not receive sufficient early exposure to the germs needed to develop properly. This is known as the hygiene hypothesis.
It's rare for someone to have anallergic reaction to food additives. However, certain additives may causea flare-up of symptoms in people with pre-existing conditions.
Sulphur dioxide (E220) and other sulphites (E221, E222, E223, E224, E226, E227 and E228) are used as preservatives in a wide range of foods, especially soft drinks, sausages, burgers, and dried fruits and vegetables.
Sulphur dioxide is produced naturally when wine and beer are made, and is sometimes added to wine. Anyone who has asthma or allergic rhinitis may react to inhaling sulphur dioxide.
A few people with asthma have had an attack after drinking acidic drinks containing sulphites, but this isn't thought to be very common.
Food labelling rules require pre-packed food sold in the UK, and the rest of the European Union, to show clearly on the label if it contains sulphur dioxide or sulphites at levels above 10mg per kg or per litre.
Benzoic acid (E210) and other benzoates (E211, E212, E213, E214, E215, E218 and E219) are used as food preservatives to prevent yeasts and moulds growing, most commonly in soft drinks. They occur naturally in fruit and honey.
Benzoates could make the symptoms of asthma and eczema worse in children who already have these conditions.
A food allergy is when the body's immune system reacts unusually to specific foods. Allergic reactions are often mild, but they can sometimes be very serious.
Symptoms of a food allergy include a raised, itchy red rash, swelling of the face, eyes, lips and tongue, and shortness of breath.
A food allergy is caused when your immune system mistakenly treats harmless proteins found in certain foods as a threat. It releases a number of chemicals, which then triggers an allergic reaction.
If you think you or your child has a food allergy, make an appointment with your GP.
The advice here is primarily written for parents of a child with a food allergy. However, most of it is also relevant if you're an adult with a food allergy.
Once you have been diagnosed as having a food allergy, you will receive advice about antihistamines, adrenaline and using an auto-injector.
Alexis Manning has a peanut allergy. She first found out that she was allergic to peanuts as a child. Some sweets just tasted bad and made her lips swell a bit, and it didn't take long to work out the cause.