If you have a food allergy, your body's immune system mistakes particular foods, for example eggs or nuts, as harmful. An allergic reaction to food can cause a range of symptoms.
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 might be.
Food allergies in young children are more common than in adults, but many children outgrow them by school age. It's possible to develop a food allergy as an adult, even if you never had allergies as a child.
Food and the immune system
If you have a food allergy, your body mistakes certain foods as harmful, and produces antibodies. This is known as sensitisation and may not cause symptoms. However, the next time you eat the food, the antibodies are ready to react with it. This causes the body to release chemicals, which lead to a range of physical symptoms known as an allergic reaction.
Symptoms of food allergy
Some food allergies result in immediate, severe and even life-threatening symptoms (such as severe peanut allergy), whereas others cause symptoms which may take longer to develop (for example, gluten allergy, also known as coeliac disease).
You may get some or all of the following symptoms:
- itching and/or swelling of your lips, mouth, tongue and throat
- skin reactions (eg swelling and itching, eczema and flushing)
- diarrhoea, feeling sick, vomiting and bloating
- wheezing or shortness of breath
- runny nose
- sore, red and itchy eyes
You may also have symptoms that affect your whole body, such as:
- extreme tiredness
These symptoms can be caused by problems other than food allergy, so you should visit your GP for advice.
Complications of food allergy
Sometimes people have an allergic reaction to food that is triggered by exercise. Not eating for a couple of hours before exercise may prevent this problem.
Some people develop a severe, whole-body allergic reaction called anaphylaxis, or anaphylactic shock; a rare but potentially fatal allergic reaction. Symptoms can include dizziness, a rapid pulse, a rapid drop in blood pressure and swelling of the airways and throat, making it difficult to breathe. This could result in loss of consciousness if left untreated.
Causes of food allergy
Problem foods include peanuts, tree nuts (including macadamia and Brazil nuts, pecans, cashews, pistachios, almonds, hazelnuts and walnuts), fish and shellfish, cows' milk, eggs, soya and wheat.
If you have one food allergy, you may also react to other foods (cross-reactivity). For instance, if you're allergic to prawns, other shellfish may also affect you. People with hay fever or an allergy to latex may also have a cross-reaction to certain foods.
The diagnosis of a food allergy isn't always straightforward. Many food allergy symptoms can also be caused by a number of other conditions and it may take some time before the problem food is identified and your doctor can confirm that you have an allergy.
Your GP will ask you about your symptoms and examine you. He or she may also ask you about your medical history. Some examples of questions you might be asked are listed below.
- How quickly did the reaction start?
- Did you take treatment (eg antihistamines) and did it work?
- Do you always get this reaction to the food? How much did you eat?
- Did anybody else eating the food get ill?
- How was the food cooked and stored?
- Do you have a family history of eczema, asthma, hay fever or food allergy?
If an allergy seems likely, your GP may refer you for testing at a specialist allergy clinic.
Elimination and challenge diets
An allergy specialist may ask you to remove the suspected allergy food from your diet and replace it with another food. If your symptoms improve, a diagnosis can usually be made.
To confirm this diagnosis, your doctor may then ask you to re-introduce the food back into your diet. If you have had severe allergy symptoms in the past, this will be done under medical supervision in hospital.
It's important, particularly for children, that you don't cut out food groups without first getting medical advice, as you could risk missing out on essential nutrients.
Skin prick tests
In a skin prick test, an extract of the suspect food is put on a small patch of skin, usually on your forearm or back, and a very small, fine scratch is made. If redness and swelling develops around the scratch, the test is positive for that food.
However, you can develop a positive reaction to this type of test without having allergic symptoms when you eat the food. These 'false positives' mean that the test isn't always completely reliable, so it's usually used in combination with other tests.
Again, there is a small risk if you have had severe allergic reactions in the past and therefore these tests are always carried out in hospital.
Blood tests are useful if you have a severe food allergy and are at risk of anaphylaxis or if you have extensive eczema or dermatitis and can't have a skin test. The RAST (radioallergeosorbent) test measures levels of food-specific antibodies in your blood. This test can result in false positive results (as in skin prick tests), or in false negative results (when your body produces antibodies but they aren't circulated in the blood).
Unproven allergy tests
Numerous tests that claim to detect allergies are available by mail order or online, through health food shops, sports centres and complementary practitioners. These include hair testing, electro-acupuncture, and various kinds of blood test.
There is no scientific evidence to prove that these tests have any value in diagnosing or managing food allergy. They can be expensive, and may give a worrying false positive result, or false reassurance. For this reason, the Royal College of Pathologists of UK recommends that you don't use them.
Treatment of food allergy
Managing food allergies
Some people outgrow their food allergies, especially children. However, this is unlikely with allergies to nuts and fish.
The only treatment for food allergy is not to eat the problem food. A registered dietitian can help you identify and remove a problem food from your diet and replace it with alternatives, to make sure you don't miss out on essential nutrients. Your dietitian can also explain what you need to look for on food labels and when eating out. Symptoms of mild food allergies, such as a rash or runny nose, may be treated with antihistamines. However, it's important that you only take medicines for your allergy on the advice of your doctor. Always read the patient information leaflet that comes with your medicine and if you have any questions, ask your pharmacist for advice.
People with severe food allergies who are at risk of anaphylaxis need to take certain precautions. Despite reading menus and ingredients lists carefully, it's easy to eat a problem food by accident. Even a tiny amount of a problem food can trigger a severe reaction.
- Make sure that your doctor teaches you how to cope if you have an allergic reaction.
- Wear a bracelet or carry a card that gives details about your allergy.
- Carry a pre-loaded adrenaline syringe (eg EpiPen). You must know how to use it in case you have an anaphylactic reaction. Check regularly to make sure that it's in full working order and within its expiry date. If you use this, you must always seek medical attention immediately afterwards.
- Let your family, friends and work colleagues know of your allergy, and how they can help in the event of an emergency.
- If your child has a severe allergy, you must make sure that all their carers and teachers have the knowledge and ability to react correctly in an emergency.
This information was published by Bupa's health information team and is based on reputable sources of medical evidence. It has been peer reviewed by Bupa doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional.
1. How can I prevent my child from developing food allergies and will they grow out of them?
There are no proven ways to predict whether your child will have food allergies or to prevent your baby from developing them. However, a child born into a family with a history of allergies is more likely to develop food allergies than a child with no family history.
Food allergies are more common in children than in adults. In most cases, a food allergy won't continue into adulthood but will disappear altogether or will be replaced by a different kind of allergy (such as an allergy to pollen, dust mites etc). The most common food allergies in children are to peanuts and tree nuts (such as Brazil nuts, hazelnuts and walnuts), cows' milk, hens' eggs, wheat, fish and soya.
Pregnancy and breastfeeding
If you're pregnant or breastfeeding and are on a restricted diet because of a severe food allergy, you should check with your dietitian that you're getting all of the nutrients you need to stay healthy while pregnant or breastfeeding.
Babies are, to a certain extent, exposed to the foods eaten by their mothers when in the womb and during breastfeeding. The British Nutrition Foundation recommends that women who are pregnant and breastfeeding shouldn't eat peanuts or peanut-containing foods if there is a close family history (mother, father or siblings) of allergies such as food allergy, asthma, eczema or hay fever. If there is no family history of allergy, there is no need to prevent exposure to peanuts in babies, in fact some researchers believe, preventing a child from eating peanuts may put him/her at greater risk of developing an allergy. This is because if babies are exposed to tiny quantities of peanut during pregnancy and breastfeeding, it may help them to tolerate peanuts in the future. Research into this area is ongoing.
It has been shown that breast-fed babies are less likely to develop allergies or eczema than bottle-fed babies. The World Health Organization (WHO) recommending that babies are exclusively breastfed for the first six months of life. Breast-fed babies receive all the nutrients they need from their mother's milk, together with hormones and growth factors to help them develop, and antibodies which help protect them from infections.
Talk to your health visitor about how and when to start introducing solid foods into your baby's diet (weaning). Usually, weaning isn't advised until a baby is six months old. When weaning your baby from breast or infant milk to solid foods, you should introduce new foods gradually. It's best to introduce foods one at a time and watch your baby's response carefully - keeping a food diary may help identify which foods are liked or disliked by your baby, and which foods cause any sort of reaction.
If you have a family history of allergy to a particular food, you should talk to your doctor or dietitian before introducing it to your baby. It is recommended that children with parents or siblings who have allergies shouldn't be given peanuts or foods containing peanuts until they are at least three years old. As with pregnancy and breastfeeding, if there is no family history of allergy, there is no need to stop young children eating peanuts, although you shouldn't let children under the age of five eat whole peanuts (or other types of nuts) in case they choke.
You shouldn't give wheat, rye or barley-based foods to babies younger than six months if there is someone in their family who can't eat foods containing gluten (ie they have coeliac disease).
Many children grow out of their food allergies by the time they are six or seven. However, some allergies (including fish and peanut allergies) are likely to continue into adulthood. If your child has been diagnosed with a food allergy at an early age and is under the care of an allergy specialist, it may be worth asking about having him/her re-tested in case his/her allergy has resolved.
2. I have just been diagnosed with a peanut allergy - what precautions should I take with my meals?
After diagnosis of any food allergy, it's important to get as much information as possible about how you can identify the problem food and what you should do if you're accidentally exposed to it.
Ask your GP or allergy specialist to refer you to a dietitian who will show you how to identify problem foods and how to ensure you have a healthy, well-balanced diet without them.
It is the law in Hong Kong that every pre-packed food must be clearly labelled to show whether they contain any of the eight substances, namely cereals containing gluten; crustacea and crustacean products; eggs and egg products; fish and fish products; peanuts, soybeans and their products; milk and milk products (lactose included); tree nuts and nut products; and sulphite in concentrations of 10 parts per million or more, which are known to cause allergy. Whenever you buy a pre-packed food, always check the label first, even if you have bought the product before - the recipe or method of manufacture might have changed since you last bought it. If you buy your groceries online, detailed product information and ingredient lists may not be available on the website - always check the labels of the products you have bought when they are delivered.
It's much more difficult to make sure that foods which aren't pre-packed don't contain peanuts or other problem foods. Examples of these are the foods that you might buy from sandwich shops, deli counters, salad bars, butchers, bakers or anywhere that food is weighed and sold loose. These foods won't have detailed ingredient and allergy labelling, and are also at increased risk of cross-contamination from foods which do contain peanuts or other problem foods. It may be safer, particularly if you have a severe allergy, never to buy foods which aren't pre-packed.
If you're invited for a meal prepared by friends or family, make sure they are aware of your food allergy and which foods you can't eat. Ask them to check the ingredients they use with you. If appropriate, take your own food with you.
Before booking a table at a restaurant, it's important to inform them of your allergy and make sure that they can provide you with a meal that won't give you problems. When you arrive at the restaurant, tell the waiter, waitress and chef about your allergy and make sure they appreciate how serious it is. Don't rely on the menu for accurate descriptions of the dishes - nuts may be present in the food but not as a main ingredient and therefore may not be mentioned on the menu. Before ordering any food, carefully check the ingredients with the waiter or waitress and ask them to double-check with the chef - preferably, you should speak to the chef yourself. If there is any doubt as to the suitability of a particular dish, don't order it.
Particular dishes to watch out for in restaurants are listed below.
- Malaysian, Chinese and Indian dishes - these often contain nuts or are cooked using nut oils.
- Salads - these can be garnished with nuts or dressed with nut oils.
- Desserts - nuts are often used as garnishes or may be present in the form of ground almonds or in the dessert base where they aren't immediately obvious.
- Food in self-service areas - these are at risk from cross-contamination (as in non pre-packed foods).
Before travelling and eating abroad, it's a good idea to learn how to tell people about your food allergy, learn the words to look out for on menus and become familiar with local dishes which contain nuts. You can get translation cards in many different languages which will help you.
It's important to check the ingredient lists of any medicines you take, whether this is off-the-shelf or over the counter from a pharmacy, or if it's a prescribed medicine. Your pharmacist can contact the manufacturer of your medicine to check whether the medicine contains peanuts (often as peanut oil), or if they are used in the manufacturing process.
If you have a severe allergy, you will probably have been prescribed an adrenaline pen (EpiPen) to use in case of accidental exposure to your problem food. Always have two adrenaline pens with you and check them regularly to make sure they are within their expiry dates. It's very important that you're comfortable with using your adrenaline pen and are confident that you will be able to do so in an emergency. If you have any concerns about using your adrenaline pen, discuss them with your doctor and ask for more training on how to use it. If you ever have to use your adrenaline pen, it's vital that you seek medical attention immediately afterwards.
Make sure your friends, family and work colleagues are aware of your allergy and know what to do in an emergency.
If you need any further information about your food allergy, talk to your GP or allergy specialist.
3. I ate shellfish at a restaurant last night and have been sick and have a rash on my skin - is this a food allergy?
Food allergy and food poisoning can often result in very similar symptoms and it can be difficult to decide which of these conditions is causing the symptoms.
Diarrhoea, feeling sick, vomiting and gastrointestinal discomfort can all be symptoms of both food allergy and food poisoning. However, there are some symptoms which you often get in food poisoning but not in food allergy and vice versa.
The common symptoms of food poisoning include diarrhoea, feeling sick, vomiting, abdominal cramping, pain, bloating and fever.
The common symptoms of food allergy are diarrhoea, feeling sick, vomiting and bloating, but you may also, or instead, have coughing and wheezing, runny nose, sore, red and itchy eyes, itching and/or swelling of your lips, mouth, tongue and throat, skin reactions (swelling, itching, rash, eczema), fainting and collapse.
These symptoms may also be caused by problems other than food allergy or food poisoning. Your GP is the best person to advise you as to whether you have a food allergy, food poisoning or another condition and what treatment you need.
In addition to thinking about the types of symptoms you're experiencing, consider the following points.
- If you have had similar symptoms with this type of food before, it's possible that you may have a food allergy or an intolerance to this type of food.
- If you have a history of allergic disease, or someone in your close family does, you're more likely to have allergies.
- If other people eating the same food have had similar symptoms, this suggests that there was a problem with the food itself. Contact the restaurant and/or the local health department to find out if they have had any other similar reports.