Food allergy

A food allergy is when your body's immune system reacts to particular foods, for example eggs or nuts, which it sees as harmful. Most food allergy reactions are mild, but sometimes they can be life-threatening and even fatal.

About food allergies

If you have an allergy, it means that your body's immune system reacts to a substance called an allergen. Allergens aren't usually harmful and most people aren't sensitive to them.

An allergic reaction happens after your immune system mistakes an allergen, for example nuts, for a harmful invader and produces antibodies. The first time you eat or touch the specific food your body doesn’t react, and you don’t have symptoms. This is called sensitisation. However, the next time you eat or touch the food, your antibodies are ready to react with it. This causes your body to release chemicals, which leads to a range of symptoms called an allergic reaction.

Foods that cause allergies include peanuts, sesame, tree nuts (Brazil nuts, almonds, cashews, hazelnuts, walnuts and pecans), fish and shellfish, cow’s milk, eggs, soya and wheat.

Food allergies in young children are more common than in adults, but many children grow out of allergies as they get older. You can develop a food allergy as an adult, even if you never had allergies as a child. In the UK, about one to two in 100 people have a food allergy.

If you have hay fever or an allergy to latex, you may also find that you’re allergic to certain foods. This is called cross-reactivity.

A food allergy is sometimes confused with food intolerance or food poisoning. These can make you feel ill but they aren't usually harmful in the same way that a true food allergy can be.

Symptoms of food allergy

The symptoms you get during an allergic reaction depend on where in your body chemicals are being released, and how severe your allergy is. If you have a very severe reaction, called an anaphylactic reaction, your whole body may be affected.

Your symptoms will usually develop within a few minutes of eating or touching the food that causes your allergic reaction. However, some food allergy symptoms can take a few hours to develop. The main symptoms may include:

• itchy or swollen lips, mouth, tongue and throat
• a skin reaction, for example hives, a rash or flushed skin
• wheezing, noisy breathing or shortness of breath
• diarrhoea, feeling sick, vomiting and feeling bloated (swollen abdomen)
• coughing
• a runny or blocked nose
• sore, red and itchy eyes

These symptoms may be caused by problems other than food allergy. If you think you may have a food allergy, see your GP for advice. If you have a severe reaction or have trouble breathing, you may need to seek urgent medical attention.

If you're severely allergic to a food, then you can have an allergic reaction by just touching or being near the food, or by being near someone who is eating it.

Complications of food allergy

The main complication of food allergies is anaphylaxis. This is a severe, full-body allergic reaction which can be life-threatening. If you have an anaphylactic reaction to a food, you may have breathing problems, your airways can swell and you can quickly collapse and become unconscious. If you think someone is having an anaphylactic reaction, call for emergency help. Food allergies are more likely to trigger an anaphylactic reaction in children than adults. However, this type of reaction is rare, with less than one in 1,000 people having an anaphylactic reaction at some time in their lives.

Causes of food allergy

The exact reasons why some people have food allergies and others don’t aren't fully understood.

Most people with a food allergy have a type called an IgE-mediated allergy. This usually happens within a few minutes of eating or touching a specific food. The reason why this happens isn’t yet known. However, experts think that a number of things together may cause this type of allergic reaction, such as your genes and the environment you live in.

The second type of food allergy is known as a non-IgE-mediated food allergy and develops because of cell reactions in your immune system. It happens several hours or days after you have eaten the food and your symptoms, such as eczema and diarrhoea, usually last longer than symptoms from an IgE-mediated reaction.

If you have other allergies or conditions, such as eczema or asthma, you may be more likely to develop a food allergy. This is called atopy. If someone else in your immediate family has these conditions, for example your parents, you’re more likely to have an allergy, although it may not be to the same thing.

Diagnosis of food allergy

Your GP will ask about your symptoms and examine you. He or she will ask you questions about your allergic reaction including how quickly it develops, how severe it is and what you think may have caused it.

If your GP thinks you may have a food allergy, he or she may carry out a skin prick or radioallergosorbent (RAST) test, or refer you to a specialist allergy clinic for tests. Common allergy tests are listed below.

• Skin prick tests. A small and diluted amount of the possible food allergen is put on your skin and a very small, fine scratch is made through it. If your skin becomes red and swollen around the scratch, your test is positive for that particular food.
• Blood tests. These are called RAST tests and can measure the amount of antibodies in your blood to a suspected food allergen. You may have a blood test if you can’t have a skin prick test for some reason, for example, if you have severe eczema.
• Elimination diets. This is when you stop eating the food or foods that may be causing your allergic reaction to see whether your symptoms get better. If they do, you then start eating the suspected food again to see if your symptoms come back. If they do, it’s likely that you’re allergic to that food.
• Food challenges. If you have a severe food allergy, you will be given a small amount of the food which may be causing your allergic reaction, to see what happens. You should only have this type of test done in a hospital or clinic, where you can be treated quickly if you do have a severe reaction.

There are many other tests available for food allergies, such as applied Kinesiology, hair analysis and Vega testing, but none of these has been shown to be effective at testing for food allergy.

Living with a food allergy

Many children grow out of food allergies, such as cow’s milk, eggs and wheat allergies, as they get older. Around two in 10 children outgrow an allergy to peanuts.

Most food allergy reactions are mild, though they can be uncomfortable and distressing.

There isn't a cure for food allergy. However, you can prevent a reaction by not eating the food that you're allergic to. If you do eat or come into contact with the food that causes a reaction, you can treat the symptoms yourself.

You can buy antihistamines at your pharmacy without a prescription. These medicines help to dampen down your body’s response to an allergen and can help to ease your symptoms. Some antihistamines can make you feel drowsy. Always read the patient information leaflet that comes with your medicine and if you have any questions, ask your pharmacist for advice.

If you have a severe food allergy, ask your GP or allergy specialist to refer you to a dietitian. Your dietitian can show you how to identify problem foods and how to make sure you have a healthy, well-balanced diet without them.

If you have a food allergy, it makes sense to try and not eat the food or foods that cause you to react. The following tips may help.

• Check the labels on foods carefully, to find out if they contain what you're allergic to. There are laws that food manufacturers have to work to that mean that all pre-packed food sold in the UK and the European Union must say on the label whether it contains an allergen, such as eggs or nuts.
• Take extra care when you’re cooking at home, to make sure you don’t contaminate your food with any foods that you’re allergic to. This may mean keeping certain foods, utensils and chopping boards separate and always clean utensils, chopping boards and surfaces directly after use.
• When you’re eating out, read menus carefully and tell staff about your food allergy. Take extra care where foods can be easily contaminated, such as buffets and parties.
• Take care when you’re buying foods that aren’t pre-packed, for example foods that you might buy from sandwich shops, deli counters or bakeries. These foods won't have detailed ingredients and allergy labelling, and may also be contaminated by other foods.

Emergency treatment of food allergy

Most allergic reactions won’t require emergency treatment. However, if you have a severe food allergy and have an anaphylactic reaction to it, you can give yourself an injection of adrenaline as soon as your symptoms start. Adrenaline is a hormone (a chemical that occurs naturally in your body) that relaxes your muscles and helps to reduce any swelling, which makes it easier to breathe. It works very quickly and starts treating your reaction straight away.

Your doctor can prescribe a single dose of adrenaline in the form of a pen. This is a pre-loaded syringe containing adrenaline that you can inject yourself. Once you have injected the adrenaline, or someone has done it for you, you should call an ambulance and get further medical help immediately. Although adrenaline works very quickly, it doesn’t work for very long and you’re likely to need more treatment.

Produced by Rebecca Canvin, Bupa Health Information Team, January 2013.

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