Most true food allergies occur when the immune system reacts to a protein in food. This protein is known as an allergen. When the immune system mistakenly treats it as harmful, it triggers a response that can cause symptoms ranging from mild skin reactions to more serious breathing difficulties.
This article explains why food proteins trigger allergies, how allergy differs from intolerance, what symptoms to look for, and when a GP assessment is appropriate.
Key Takeaways
- Most true food allergies are triggered by proteins found in food.
- Sugar and fat are not common triggers of a true allergic immune response.
- Food allergy involves the immune system; food intolerance usually does not.
- A positive allergy test alone does not confirm a clinical food allergy.
- Severe breathing symptoms or collapse require emergency care and a call to 000.
What Component of Food Causes an Allergic Reaction?
Most true food allergies are triggered by a protein in food. The immune system mistakes this protein for a threat and releases chemicals such as histamine, causing allergy symptoms.
The trigger differs between foods and people. For example, cow’s milk allergy involves milk proteins, while lactose intolerance involves difficulty digesting lactose, the natural sugar in milk.
Why Can a Food Protein Trigger an Allergy?
In food allergy, the immune system reacts to a normally harmless food protein. Immediate IgE-mediated reactions can affect the skin, digestive system, breathing or circulation.
Some food allergies are non-IgE-mediated and may cause delayed symptoms, particularly involving the digestive system.
Which Foods Commonly Contain Allergens?
In Australia, the foods responsible for most food allergies include:
- milk
- egg
- peanut
- tree nuts
- sesame
- wheat
- soy
- lupin
- fish
- crustaceans and molluscs
Australian food-labelling rules require these allergens to be declared when present as ingredients or as components of additives or processing aids. Individual tree nuts must be named separately on the label. Many other foods can also cause allergy, and a person may react to one food while tolerating related foods. This list should not be used for self-diagnosis.
Can Sugar, Fat or Food Additives Cause a Reaction?
Food proteins usually trigger true allergies, while sugars and fats are less common causes. Lactose causes intolerance rather than milk allergy.
Additives, preservatives and food chemicals may cause other reactions. Sulphites can trigger breathing symptoms in some people with asthma, although severe reactions are rare.
Food Allergy vs Food Intolerance What Is the Difference?
These two terms are often confused, but they are not the same thing.
| Food allergy | Food intolerance |
| Involves the immune system | Usually does not involve the immune system |
| Often triggered by a food protein | May involve sugars, food chemicals, or digestion difficulty |
| Small amounts may cause a reaction | Symptoms may depend on the amount consumed |
| Can cause anaphylaxis | Usually does not cause anaphylaxis |
Symptoms can overlap between the two conditions. The timing, amount eaten, and full reaction history matter more than a self-applied label when working out the likely cause.
What Symptoms Can a Food Allergy Cause?
Symptoms can vary between people and between reactions. They may include:
Mild to moderate symptoms
- hives, welts, or skin redness
- swelling of the face, lips, or eyes
- tingling in the mouth
- abdominal pain or vomiting
Severe symptoms
- difficulty or noisy breathing
- swelling or tightness of the tongue or throat
- wheeze or persistent cough
- difficulty speaking
- dizziness, collapse, or a pale, floppy appearance in a young child
Immediate IgE-mediated reactions usually begin within minutes and may occur within one or two hours. Some non-IgE-mediated food allergies cause delayed digestive symptoms two or more hours later, depending on the condition.
When Is a Food Reaction an Emergency?
If any of the following occur after eating, seek emergency help immediately:
- difficult or noisy breathing
- tongue or throat swelling
- wheezing or persistent cough
- difficulty speaking or swallowing
- dizziness, collapse, or loss of consciousness
If an adrenaline autoinjector is available, use it immediately, then call 000 for an ambulance. Follow the person’s ASCIA Action Plan if one is available. Do not wait to see if symptoms improve on their own.
How Does a GP Assess a Possible Food Allergy?
Assessment begins with the clinical history, not a test panel. During a GP assessment of a possible food reaction, your doctor will usually ask:
- which food and ingredients were eaten
- how much was consumed
- how quickly symptoms appeared after eating
- which symptoms occurred and how long they lasted
- whether the food was previously tolerated without a problem
- whether the reaction has happened more than once
- whether eczema, asthma or another allergy is present
For a children’s health appointment, the same history is gathered with the parent or caregiver present.
Depending on the history, a GP may discuss targeted specific-IgE blood testing or referral to an allergist. Current ASCIA food-allergy testing guidance explains that a positive skin-prick or blood test result may show sensitisation, but it must be interpreted alongside the clinical history.
Should You Remove the Suspected Food From the Diet?
Do not repeatedly expose a child or adult to a suspected trigger at home to test the reaction. Equally, avoid removing major foods such as milk, wheat, or egg from a child’s diet without professional advice. Removing important food groups without guidance may affect nutrition, particularly in young children. A GP or dietitian can advise on safe alternatives where needed.
Understanding the Trigger Is the First Step
Most true food allergies involve an immune response to a food protein, but similar symptoms may also result from an intolerance, food chemicals or another condition. A GP can review the food, symptoms and timing to guide appropriate assessment.
Patients in Valentine, NSW can contact Valentine Healthcare to discuss a suspected reaction, appointment options and any fees or Medicare rebates that may apply.
Patients in Valentine, NSW can contact Valentine Healthcare to discuss a suspected food reaction, appointment options, and consultation fees and Medicare rebates that may apply.
FAQs
What component of food usually causes an allergic reaction?
Most true food allergies are triggered by a protein in food. The immune system mistakenly treats this protein as harmful and produces a response that causes allergy symptoms.
Can sugar cause a food allergy?
Sugar is not a common cause of true food allergy. Lactose, a natural sugar in dairy products, is associated with lactose intolerance, which involves difficulty digesting the sugar rather than an immune response.
Is a food allergy the same as food intolerance?
No. Food allergy involves the immune system and can cause anaphylaxis. Food intolerance does not usually involve the immune system and may cause digestive or other symptoms. Unlike food allergy, it does not usually cause anaphylaxis.
Can a blood test confirm a food allergy?
Not by itself. A positive specific-IgE blood test may indicate sensitisation, but it must be interpreted alongside the food eaten, the symptoms, and the timing of the reaction.
When should I see a GP after a food reaction?
Arrange a GP assessment after repeated or concerning symptoms. Breathing difficulty, throat swelling, dizziness, or collapse require emergency treatment and a call to 000 immediately.