An astonishing one in three of us is allergic to something, and approximately half of all allergies are food allergies. So if you have one or suspect you do – whether it is to pollen, peanuts, shellfish, milk or wheat – you are hardly alone.
With an allergy, the immune system produces a protein called an antibody to fight off the allergen that is causing the problem. In a classic allergy, an antibody called IgE is produced, triggering the release of a chemical, histamine, that usually causes a rapid, severe reaction such as swelling of the mucous membranes.
More common are allergic reactions involving the IgG antibody. This type can cause a delayed reaction – sometimes called a ‘food intolerance’ – up to 24 hours after exposure to the allergen. While not as obviously dramatic as a classic reaction, a food intolerance can seriously erode your wellbeing. Luckily it is easy to get to grips with, as you will find in this section.
Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to something in the environment that usually causes little or no problem in most people. These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis. Symptoms may include red eyes, an itchy rash, runny nose, shortness of breath, or swelling. Food intolerances and food poisoning are separate conditions.
Common allergens include pollen and certain food. Metals and other substances may also cause problems. Food, insect stings, and medications are common causes of severe reactions. Their development is due to both genetic and environmental factors. The underlying mechanism involves immunoglobulin E antibodies (IgE), part of the body’s immune system, binding to an allergen and then to a receptor on mast cells or basophils where it triggers the release of inflammatory chemicals such as histamine. Diagnosis is typically based on a person’s medical history. Further testing of the skin or blood may be useful in certain cases. Positive tests, however, may not mean there is a significant allergy to the substance in question.
Early exposure to potential allergens may be protective. Treatments for allergies include avoiding known allergens and the use of medications such as steroids and antihistamines. In severe reactions injectable adrenaline (epinephrine) is recommended. Allergen immunotherapy, which gradually exposes people to larger and larger amounts of allergen, is useful for some types of allergies such as hay fever and reactions to insect bites. Its use in food allergies is unclear.