What is a food allergy?
A food allergy is an abnormal immune reaction to food. It can present as hives and skin swelling; difficulties breathing; vomiting, diarrhoea; dizziness/collapse. In some people, food allergy causes a life-threatening reaction known as anaphylaxis.
Confirmed food allergy affects up to 3% of adults; self-reported food allergy is much more common and often confused with food intolerance where the immune system is usually not involved.
What are the symptoms of a food allergy?
Food allergy symptoms usually develop within a few minutes to two hours after eating the offending food. The common signs and symptoms include:
- Itching in the mouth
- Hives or skin itching
- Swelling of the lips, face, tongue and throat
- Wheezing, nasal congestion or breathlessness
- Abdominal pain, diarrhoea, nausea or vomiting
- Dizziness, light-headedness or fainting/collapse
Food anaphylaxis presents with a potentially life-threatening combination of: closing airways, throat swelling, sudden drop in blood pressure and a rapid heart rate with dizziness, light-headedness or loss of consciousness. Emergency treatment with adrenaline is critical to avoid long-term complications or death.
In food allergy, the immune system mistakenly identifies a specific food as a ‘danger signal’ and produces antibodies (immunoglobulin E, IgE) against this allergy-causing food (allergen). On subsequent exposure to the same food, IgEs start an allergic response that can cause symptoms listed above.
Common food allergies
The most common food allergens in adults include:
- Shellfish (prawn, lobster, crab)
- Peanuts and tree nuts, such as cashew and walnuts
Less commonly adults react to:
- Cow’s milk
Oral allergy syndrome
Oral allergy syndrome affects many people with hay fever. Proteins (PR10 proteins) in certain raw fruits, vegetables, nuts and spices cause oral tingling, itching and throat discomfort due to their similarity to proteins in pollen (allergen cross-reactivity). Cooked foods are usually tolerated. Silver birch pollen allergic patients report problems when eating raw apples, cherries, peaches, and plums. Those allergic to grass pollen can have oral reactions to kiwi, tomato, cucumber, melon etc.
Exercise-induced food allergy
Eating certain foods (especially containing wheat (omega 5 gliadin allergy) or fruits with lipid transfer proteins) can cause severe allergic reactions when combined with exercise. An allergist can diagnose this condition with the relevant skin and blood tests.
Food allergy is more common in adult patients with a family history of allergy; history of other food allergies and asthma. Food anaphylaxis is more common in patients with (poorly controlled) asthma and teenagers (risk seeking behaviour). Delayed use of adrenaline and no skin symptoms on exposure to food can delay management of anaphylaxis. It is crucial to:
- be aware of one’s allergy
- review food labels
- carry adrenaline auto-injectors and wear a medical alert bracelet
- be careful when eating out
- educate friends and family about food allergy
- have a written anaphylaxis management plan