Food allergies

What is a food allergy?

A food allergy is a type of allergic reaction in which the body’s immune system reacts to specific proteins found in food, mistaking them as a threat. Food allergy symptoms can vary from mild to severe; a severe food allergy reaction causing anaphylaxis can be life threatening¹.

Types of food allergy

There are 14 major food allergens that can trigger these allergic reactions. The major allergens are: milk, eggs, nuts, peanuts, fish, shellfish (crustaceans and molluscs), soya or soybeans, mustard, celery, sesame, lupin, cereals containing gluten, and food additives such as sulphites².

What are the symptoms of food allergy?

There are a range of food allergy symptoms. Food allergy reactions typically occur seconds to minutes after ingesting and can involve:

• Skin reactions such as hives (usually a raised, itchy red rash)
• Breathing/throat problems such as tingling or itching in the mouth, tongue or throat; swelling of the face, throat or mouth (angioedema); difficulty swallowing; shortness of breath/wheezing
• Gastrointestinal issues, for example nausea or vomiting; abdominal pain; diarrhoea
• Other food allergy symptoms including dizziness; lightheadedness; hay fever-like symptoms¹.

Symptoms of food allergies range in type and severity

There are some food allergy reactions that cause mild symptoms, however there are some severe food allergies that can cause anaphylaxis or anaphylactic shock, which is a medical emergency. Symptoms of anaphylaxis include a swollen tongue, breathing difficulties, tight chest, trouble swallowing or speaking, feeling dizzy or faint, and loss of consciousness. Other food allergy reactions can take several hours to develop, making them much harder to diagnose¹.

Food allergy symptoms also vary based on the type of allergen. For example, peanut allergy symptoms are commonly swelling of the lips, eyes, and face, along with a runny nose and sneezing³. Milk allergy symptoms are often of gastrointestinal nature, such as stomach cramps, bloating and diarrhoea, particularly when the reaction is slow⁴.

What causes a food allergy reaction?

When foods containing allergens are ingested, the body identifies the food allergen as an invader and produces an inflammatory response. There are three different types of food allergy, classified based on the body’s immune response to allergens. IgE-mediated food allergies trigger the stimulation of the immunoglobulin E (IgE) antibody, causing the release of immune chemicals, such as histamines and cytokines. These types of responses are more likely to cause anaphylaxis¹. Non-IgE-mediated food allergies, caused by other immune cells, such as T cells, are less common and the immunologic mechanism is poorly understood⁵. Some patients may also experience a mixed IgE and non-IgE-mediated reaction¹.

How are food allergies diagnosed?

When diagnosing a food allergy, a food intolerance should first be ruled out. Though food intolerances can present with similar symptoms of food allergies, food intolerances do not elicit an immune response and the severity of food allergy symptoms is determined by the amount of food eaten. Thus, when diagnosing a food allergy, the extent of a patient’s symptoms, along with medical history, should be carefully considered. If there is a suspected food allergy, then a skin-prick or blood test should be carried out in an allergy clinic. If the onset of food allergy symptoms is slow, an elimination diet can help in identifying food allergies. Other food allergy tests include vega testing, kinesiology testing, hair analysis and leukocytotoxic tests¹.

How are food allergies treated?

Food allergy treatment depends on the severity of the food allergy. Antihistamines are used to treat mild to moderate food allergies, whilst adrenaline is used to treat severe allergic reactions and anaphylaxis. Research is ongoing in which the patient is gradually exposed to the trigger food or protein in escalating doses to increase the threshold that triggers a reaction, for example oral immunotherapy (OIT), sublingual immunotherapy (SLIT) and epicutaneous immunotherapy (EPIT). There is also ongoing research on the potential for anti-IgE treatments, and combination of anti-IgE with oral OIT, to dampen the immune over-reaction to food allergens^6,7,8,9.

References

1. NHS, 2019. Available at: https://www.nhs.uk/conditions/food-allergy/ (accessed April 2021). 
2. Food Standards Agency, 2020. Available at: https://www.food.gov.uk/business-guidance/allergen-guidance-for-food-businesses (accessed March 2021). 
3. AllergyUK, 2021. Available at: https://www.allergyuk.org/information-and-advice/conditions-and-symptoms/778-peanut-allergy (accessed April 2021). 
4. Healthline, 2021. Available at: https://www.healthline.com/health/allergies/milk - symptoms (accessed April 2021). 
5. Cianferoni A. Non-IgE Mediated Food Allergy. Curr Pediatr Rev. 2020;16(2):95-105. 
6. Hussey Freeland DM, Manohar M, Andorf S, Hobson BD, Zhang W, Nadeau KC. Oral immunotherapy for food allergy. Semin Immunol. 2017;30:36–44. 
7. Food Allergy Research & Education, 2021. Available at: https://www.foodallergy.org/resources/sublingual-immunotherapy-slit (accessed April 2021). 
8. Food Allergy Research & Education, 2021. Available at: https://www.foodallergy.org/resources/epicutaneous-immunotherapy-epit (accessed May 2021). 
9. Michelet M, Balbino B, Guilleminault L, Laurent RL. IgE in the pathophysiology and therapy of food allergy. Eur. J. Immunol. 2021;51:531–543.