Food allergy

Author: Hon A/Prof  Amanda Oakley, Dermatologist, Hamilton, New Zealand, 2008.

What is food allergy?

Food allergy is an immunological reaction to a food protein that is either immediate (occuring seconds to minutes after eating or touching the food item) or delayed (occurring hours or days later). Allergic reactions may occur when the affected person eats or touches a tiny amount of the responsible protein.

Food allergy is most common in young babies (4%), who often outgrow their allergies. About 2% of adults also suffer from allergy to one or more foods. The tendency to food allergy runs in families.

Food allergy and the skin

Skin conditions due to food allergy include:

Other symptoms from food allergy

Food allergy may result in the following symptoms:

Respiratory allergy
  • Hay fever (rhinitis) i.e., sneezing, running/itchy eyes
  • Asthma i.e., wheezing, difficulty in breathing, cough
Gastrointestinal allergy
  • Nausea and vomiting
  • Heartburn, reflux
  • Colic, cramps, diarrhoea, constipation
  • Irritable bowel syndrome (IBS)
Circulatory allergy
  • Anaphylaxis: low blood pressure, shock

What foods cause allergic reactions?

About 90% of systemic allergic reactions are due to the following food items:

There are numerous other foods and plants that occasionally cause allergy. Some are listed here.

Allergy may also be provoked by preservatives such as parabens, and flavouring agents or fragrances added to foods.

How is food allergy diagnosed?

Food allergy is diagnosed by taking a careful history of the symptoms and their relationship to food, supported by examination findings and the results of tests. Unfortunately, neither history nor tests are entirely reliable in everyone.

The main tests for food allergy are:

Food intolerance

Not all reactions to food are allergic in origin. Intolerance can cause similar symptoms to allergy, including urticaria and dermatitis. But the reaction often depends on how much is consumed. These reactions are classified as follows.

Food deficiencies

Skin conditions may also be due to deficiencies in the diet, sometimes because of attempts to reduce exposure to known or presumed allergens.

What is the treatment for food allergy?

The mainstay of management is to identify which foods are responsible for reactions, and then to avoid them. Prescribed treatments depend on symptoms, and may include:

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