What are Food Allergies

The body's immune system keeps you healthy by fighting off infections and other dangers to good health. A food allergy reaction occurs when your immune system overreacts to a food or a substance in a food, identifying it as a danger and triggering a protective response.

While allergies tend to run in families, it is impossible to predict whether a child will inherit a parent's food allergy or whether siblings will have a similar condition. Some research does suggest that the younger siblings of a child with a peanut allergy will have a much higher risk of being allergic to peanuts.

Types of allergic reactions

There are two types of food allergy depending on how the immune system reacts.

  1. Symptoms that are 'immediate' (quick to appear) are caused by an antibody called immunoglobulin E (IgE). Antibodies are proteins made in the immune system that attack substances which the body identifies as being "foreign" or "toxins". These substances are called antigens. Usually, these allergic symptoms happen within minutes of eating the offending food or up to two hours after eating. This type of reaction is described as IgE- mediated food allergy.
  2. Non-IgE-mediated food allergy still involves the immune system over-reacting to a food trigger, but in a different way to IgE-mediated food allergy. Symptoms are 'delayed' and take longer to develop. The symptoms may take up to two days to appear. If the offending food continues to be eaten in the diet, the immune system will continue to produce the symptoms over days or even weeks.

Food intolerances do not involve the immune system and are different from food allergy. Symptoms are usually much slower to develop and often require larger amounts of the food to be eaten. Many food intolerances involve the digestive system and often cause symptoms such as bloating, diarrhoea, nausea and tiredness. As there are no validated tests to diagnose food intolerances, a diagnosis can be difficult to reach (tests for food allergy, such as skin prick tests and blood tests, are not able to diagnose food intolerances). Always consult a medical expert if you think you may be suffering from a food intolerance.

The focus of our website is on IgE-mediated food allergy, where symptoms appear quickly after eating. Symptoms of this type of food allergy can range from mild to severe. Just because an initial reaction causes few problems doesn’t mean that all reactions will be similar; a food that triggered only mild symptoms on one occasion may cause more severe symptoms at another time.

While any food can cause an adverse reaction, eight types of food account for about 90 percent of all reactions:

  • Eggs
  • Milk
  • Peanuts
  • Tree nuts
  • Fish
  • Shellfish
  • Wheat
  • Soy

There are some foods which trigger food allergy reactions and are more problematic in certain regions of the world. These include mustard seeds (the main ingredient in the condiment mustard and celery in Europe and buckwheat in Japan). In Singapore, there have been instances of bird nest allergy. We have also reported cases of Galacto-oligosaccharides (GOS) allergy in both infants and adults. GOS which is a prebiotic found in milk formulas.

Non-IgE mediated Food Allergy

Another type of delayed food allergy reaction stems from specific food proteins that cause immune responses resulting in delayed inflammation in the skin or gastrointestinal tract, most of which can occur several hours to several days after ingestion of the food protein. These symptoms may include delayed eczema, delayed vomiting and diarrhoea, loose and frequent bowel actions, blood or mucous in the stools, failure to thrive in infants, severe colic or reflux. Specific conditions such as cow’s milk protein allergy, food protein–induced enterocolitis syndrome (FPIES), protocolitis and food protein induced enteropathy.

Food protein-induced enterocolitis syndrome (FPIES), is a severe gastrointestinal reaction that generally occurs two to six hours after consuming milk, soy, certain grains and some other solid foods. It mostly occurs in young infants who are being exposed to these foods for the first time or who are being weaned. FPIES often involves repetitive vomiting and can lead to dehydration. In some instances, babies will develop bloody diarrhoea. Because the symptoms resemble those of a viral illness or bacterial infection, diagnosis of FPIES may be delayed. FPIES is a medical emergency that should be treated with IV rehydration. Allergic Protocolitis is a condition that results in bloody stools in mostly exclusively breastfed infants who are growing well and whose mother is consuming significant amounts of dairy in her diet. Eosinophilic oesophagitis (EOE) is a recognised chronic allergic condition which is not outgrown. More patients are being diagnosed with this condition due to an increased incidence of EOE. The symptoms of EOE vary with age and include difficulty with swallowing food, recurrent vomiting, poor growth in children and food refusal.

Managing Food Allergies

Living with Food Allergies


Managing Food Allergies

Symptoms of an allergic reaction may involve the skin, the gastrointestinal tract, the cardiovascular system and the respiratory tract. They can surface in one or more of the following ways:

  • Vomiting and/or stomach cramps
  • Hives
  • Shortness of breath
  • Wheezing
  • Repetitive cough
  • Shock or circulatory collapse
  • Tight, hoarse throat; trouble swallowing
  • Swelling of the tongue, affecting the ability to talk or breathe
  • Weak pulse
  • Pale or blue coloring of skin
  • Dizziness or feeling faint
  • Anaphylaxis, a potentially life-threatening reaction that can impair breathing and send the body into shock; reactions may simultaneously affect different parts of the body (for example, a stomachache accompanied by a rash)

Most food-related symptoms occur within two hours of ingestion; often they start within minutes. In some very rare cases, the reaction may be delayed by four to six hours or even longer. Delayed reactions are most typically seen in children who develop eczema as a symptom of food allergy and in people.


Anaphylaxis is a severe, potentially life-threatening allergic reaction. It is a medical emergency affecting more than one body system such as the airways, heart, circulation, gut and skin.

What are common triggers (causes) of Anaphylaxis?

  1. Food (most common cause)
  2. Medication
  3. Insect stings

How does Anaphylaxis happen?

When a person is exposed to the trigger that he/she is allergic to, the body releases a large amount of chemicals into the bloodstream. These chemicals then cause the symptoms of anaphylaxis. Symptoms may start within seconds or minutes of exposure to the substance the person is allergic to and will usually progress quickly.

What are the Symptoms of Anaphylaxis?

The symptoms include (but may not all be experienced during one reaction)

  1. Skin rashes and hives anywhere on the body
  2. Swollen eyes, lips, tongue and mouth
  3. Difficulty breathing, severe asthma, coughing, hoarse voice
  4. Tummy pain, nausea, vomiting
  5. Fast heartbeat, dizziness, fainting, sudden feeling of weakness
    There may also be a dramatic fall in blood pressure. The person may also become floppy and weak and may have a sense of something terrible happening. This may lead to collapse and unconsciousness.

How is Anaphylaxis treated?

If your doctor thinks it likely that you (or your child) will suffer severe symptoms to your food allergen(s), then you may be advised to carry an adrenaline auto-injector (also known as AAI or epinephrine).

The adrenaline auto-injector prescribed in Singapore at present is EpiPen®. It is life-saving and safe to use, so you must not hesitate to give it in the event of Anaphylaxis. This adrenaline auto-injector is easy to use and designed for self-administration. If you or your child are prescribed an adrenaline auto-injector, it should be available to use at ALL times.

For further details on adrenaline auto-injectors and the instructions for use of the Epipen, please click here.

Once you have been diagnosed with a food allergy with a history of anaphylaxis or high risk of anaphylaxis, your allergist should prescribe an adrenaline auto-injector and teach you how to use it. You should also be given a written treatment plan describing what medications you have been prescribed and when the medication should be used. Check the expiration date of your adrenaline auto-injector and note it on your calendar. Remember to have the adrenaline auto-injector prescription renewed and collect the new device before the old one expires.

  • Epinephrine (adrenaline, which is the medication in the adrenaline auto-injector) is the first-line treatment for anaphylaxis, which results when exposure to an allergen triggers a flood of chemicals that can send your body into shock. Anaphylaxis can occur within seconds or minutes of exposure to the allergen, can worsen quickly and can be fatal.
  • Use the adrenaline auto-injector immediately if you experience severe symptoms such as shortness of breath, repetitive coughing, weak pulse, hives, tightness in your throat, trouble breathing or swallowing, or a combination of symptoms from different body areas, such as hives, rashes or swelling on the skin coupled with vomiting, diarrhoea or abdominal pain.
  • Repeated doses may be necessary.
  • You should call for an ambulance (or have someone nearby do so) and inform the paramedics that an adrenaline auto-injector (epinephrine) was administered and more may be needed. The person experiencing the reaction should be taken to nearest hospital emergency department and monitored for a period of time to ensure stability, this often includes a 24-hour observation in the hospital. Sometimes, a second reaction can still occur once the person has recovered from the first one and a second injection may be required. There is no data to help predict who may need a second dose of epinephrine, so this recommendation applies to all patients with a food allergy.

Allergy Action Plan

A food allergy will usually cause some sort of reaction every time the trigger food is eaten. Symptoms can vary from person to person, and you may not always experience the same symptoms during every reaction.

While food allergies may develop at any age, most appear in early childhood. If you suspect a food allergy, see an allergist, who will take your family and medical history, decide which tests to perform (if any) and use this information to determine if a food allergy exists.

To make a diagnosis, allergists ask detailed questions about your medical history and your symptoms. Be prepared to answer questions about:

  • What and how much you ate
  • How long it took for symptoms to develop
  • What symptoms you experienced and how long they lasted.

After taking your history, your allergist may order skin tests and/or blood tests, which indicate whether food-specific immunoglobulin E (IgE) antibodies are present in your body:

  • Skin-prick tests provide results in about 20 minutes. A liquid containing a tiny amount of the food allergen is placed on the skin of your arm or back. Your skin is pricked with a small, sterile probe. The test is considered positive if a wheal > 3mm (resembling the bump from a mosquito bite) develops at the site where the suspected allergen was placed.
  • Blood tests, which measure the amount of IgE antibody to the specific food(s) being tested. Your allergist will use the results of these tests in making a diagnosis. A positive result does not necessarily indicate that there is an allergy, though a negative result is useful in ruling one out.

In some cases, an allergist may wish to conduct an oral food challenge, which is considered the most accurate way to make a food allergy diagnosis. During an oral food challenge, which is conducted under strict medical supervision, the patient is fed tiny amounts of the suspected trigger food in increasing doses over a period of time, followed by a few hours of observation to see if a reaction occurs. This test is helpful when the patient history is unclear or if the skin or blood tests are inconclusive. It also can be used to determine if an allergy has been outgrown.

Because of the possibility of a severe reaction, an oral food challenge should be conducted only by experienced allergists in a doctor’s office or at a food challenge unit, with emergency medication and equipment on hand.

Can food allergies be prevented?

In the case of peanut allergy, the National Institute for Allergy and Infectious Disease (NIAID) in the US, issued new updated guidelines in 2017 in order to define high, moderate and low-risk infants for developing peanut allergy. The guidelines also address how to proceed with introduction based on risk.

The updated guidelines are a breakthrough for the prevention of peanut allergy. Peanut allergy has become much more prevalent in recent years, and there is now a roadmap to prevent many new cases.

According to the new guidelines, an infant at high risk of developing peanut allergy is one with severe eczema and/or egg allergy. The guidelines recommend introduction of peanut-containing foods as early as 4-6 months for high-risk infants who have already started solid foods, after determining that it is safe to do so under supervision and advice by an Allergist. Parents should know that most infants are either moderate- or low-risk for developing peanut allergies, and most can have peanut-containing foods introduced at home. Whole peanuts should never be given to infants as they are a choking hazard.

Clinical studies are ongoing in food allergy to help develop tolerances to specific foods. Ask your allergist if you or your child may be a candidate for one of these programmes.

Can food allergies develop later in life and can they be outgrown?

Children generally, but not always, outgrow allergies to milk, egg, soy and wheat. New research indicates that up to 20 percent of children may outgrow their peanut allergy, with slightly fewer expected to outgrow a tree nut allergy. If a food allergy develops as an adult, the chances of outgrowing the allergy are much lower. Food allergies in adults tend to be lifelong.

Although most food allergies develop when you are a child, they can, rarely, develop as an adult. The most common food allergies for adults are shellfish – both crustaceans and mollusks – as well as tree nuts, peanuts and fish. Most adults with food allergies have had their allergy since they were children.

If I'm allergic to one food, can I react to other foods too?

Cross reactions between foods

Individuals allergic to a specific food may also potentially have a reaction to other related foods. For example, a person allergic to one tree nut may be cross-reactive to others. Those allergic to shrimp may react to crab and lobster. Someone allergic to peanuts , which are actually legumes (beans) and not a not nut, may have problems with tree nuts, such as pecans, walnuts, almonds and cashews. In very rare circumstances they may have problems with other legumes.

Learning about patterns of cross-reactivity and what must be avoided is important in understanding more about an individual's food allergy.

Negative tests may be very useful in ruling out an allergy. In the case of positive tests to foods that you have never eaten but that are related to items to which you have had an allergic reaction, an oral food challenge is the best way to determine whether the food poses a danger. This should always be undertaken with your allergy physician.

Living with Food Allergies

For most people with food allergy, identifying and avoiding the trigger food is the key to avoiding a food allergic reaction. Families need to carefully check ingredient labels of food products, and learn whether what they need to avoid is known by other names. Our factsheets below provide useful tips on avoidance of the major food allergens.

Anaphylaxis UK has kindly allowed us to share their very comprehensive factsheets about food allergens with our members. However, some of the information contained within these factsheets is specific to the UK. Therefore, the information, specific to Singapore, should be read along with the Anaphylaxis UK fact sheet. Both can be accessed as downloadable and printable PDF's.

Currently, avoiding the food you are allergic to is the only way to protect against a reaction. Current programs are looking at ways to make you less sensitive, but not cure, food allergies. There are baked egg and baked milk oral immunotherapy programs, peanut, egg, milk and wheat oral immunotherapy programs in various Allergy centers around the world and in Singapore.

Preparing food at home safely for family members with food allergy

Preparing food for a member of the family with food allergy can be challenging and time consuming, however, using fresh foods as much as possible such as meat, vegetables, fruits, rice and potatoes and cooking homemade foods can make life a lot easier.

To minimise the risk of cross contamination in the home (when one food comes into contact with another and the food proteins mix) the following tips might be helpful:

  • Choose appropriate ingredients which are safe for the family member with food allergy.
  • Always read food labels carefully to ensure the food item you are using is safe.
  • Ensure all household members know not to share food and drinks.
  • Ensure that everyone who looks after your child with food allergy (relatives, helpers, friends, childcare, school) understand your child's allergies, what they should avoid and how to treat an allergic reaction.
  • Encourage your child to be independent and ask trusted adults about foods and if they are safe to eat.
  • Consider having a shelf or container in the fridge with “allergy safe” foods for your child.
  • For young children, it may be easier to manage the food allergy if the allergen is not used in the preparation of food at home.
  • Wash hands properly in warm soapy water before and after preparing food as well as eating.
  • When preparing food, take care to prevent cross contact (also referred to as cross contamination). Separate utensils and dishes should be used where necessary and washed thoroughly in warm soapy water and not just rinsed.
  • Always clean surfaces before preparing food for family members with food allergies using hot soapy water or an “all-purpose” cleaning solution.

As a family, you may decide to not have the food allergen in the home. This does make the risk of cross contamination easier to manage and can help prevent mistakes from being made.

Avoiding the major food allergens

Reading food labels

Cross contamination and preparing allergen free food safely


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