Online Allergy Training

Module 2 - Introduction

A food allergy is when the body’s immune system reacts unusually to specific foods, and the food the body reacts to is known as the allergen.  Most allergic reactions to food are mild, but some can be very serious.  The only way people can deal with a food allergy is to avoid the foods that make them ill. 

The science behind food allergy

Food allergies involve specific antibodies, mainly Immunoglobin E (IgE), in the immune system. For each food, the body manufactures a specific antibody. Immunoglobin E antibodies are designed to recognise and attack disease-causing substances such as pathogens and parasitic worms.

Allergic people have immune systems that are programmed to treat ordinary proteins from foods and other things as if they are a threat (for example cats, dogs, horses, insect stings, pollen etc.).

IgE is a two-stage process. The first stage of IgE mediated food allergy is sensitisation when the body recognises a particular substance as harmful but no symptoms are experienced. The second stage is where symptoms occur.

Common symptoms of an allergic reaction

Head Eyes – Sore, red and/or itchy
Nose – Runny and/or blocked
Lips – Swelling of the lips
Chest Chest – Coughing, wheezing and shortness of breath, alterations of heart rate
Throat – Dry, itchy and swollen throat, difficulty swallowing or speaking
Gut Nausea and feeling bloated, cramps, diarrhoea, and/or vomiting
Skin Itchy and/or a rash
Severe Difficulties with breathing, including asthmatic symptoms, a sudden feeling of weakness (a drop in blood pressure), unconsciousness and potentially life-threatening anaphylaxis.

What is the difference between a food allergy and food intolerance?

Food allergies normally causes symptoms within a few minutes of eating the food or being in contact with the substance. A food allergy involves a reaction in the immune system.

Food intolerances are more common and are caused by the body being unable to digest certain substances e.g. lactose. They are not the same as food allergies, as most do not involve the immune system. Food intolerances can make someone feel very ill and affect their long-term health. You will usually feel the symptoms of a food intolerance symptoms slower than a food allergy, and sometimes it may not be felt until a few hours after you have eaten the food. Symptoms can last for hours, even into the next day.

Coeliac disease

Coeliac disease is not an allergy or intolerance. It is an auto-immune disease, which means that the body produces antibodies that attack its own tissues.

For people with coeliac disease this attack is triggered by gluten, a protein found in wheat, rye and barley. Some people with coeliac disease also react to oats. Symptoms of coeliac disease can range from mild to severe and can include: bloating, diarrhoea, nausea, wind, tiredness, constipation, anaemia, mouth ulcers, headaches, weight loss, hair loss, skin problems, short stature, depression, infertility, recurrent miscarriages and joint/bone pain.

Some symptoms might be confused with irritable bowel syndrome (IBS) or wheat intolerance, while others might be related to stress or getting older. As a consequence, it can take some time before an accurate diagnosis is sought, or made. After diagnosis and starting a gluten-free diet these symptoms typically cease.

You can get more information at

Find out more:

Visit the food allergy section of the NHS Inform website

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