Stretch and Challenge (6)

Posted: 25th January 2018

The Science Behind Allergies.

The latest in our Stretch and Challenge series, the programme for Senior girls to explore and research a chosen topic, this week looks at Katie Fung’s presentation, ‘The Science Behind Allergies.’  This Lower V Alpha pupil leads us through some of the many allergies that affect so many people.

What is an allergy?

An allergy is the response of the body’s immune system to normally harmless substances, such as pollens, foods, and house dust mites. Whilst in most people these substances (allergens or antigens) pose no problem, in allergic individuals their immune system identifies them as a threat and produces an inappropriate response.

These are the most common 14 allergens

What happens in an allergic reaction?

When an allergic individual is exposed to a sensitizing allergen, an allergic reaction begins. An antibody response is triggered and the body makes a specific IgE, one that is able to recognize only that allergen. Immunoglobin E or IgE for short is one of 5 different classes of antibody made by our immune system. Although everyone makes IgE, those who are prone to allergic reactions make much larger quantities.

Food Science – type 1 allergy

There are millions of Mast Cells and Basophils in the body. Mast cells are found in tissues and basophils are in the blood stream. Both mast cells and basophils have over 100,000 receptors that are specific for the IgE antibody

When an allergen enters the immune system, the antigen binds to these IgE receptors on the surface of the cells. When two IgE antibodies next to each other bind to the antigen, this interaction causes the degranulation or breaking down of the mast cell or basophil.

As degranulation occurs, it causes the mast cell or basophil to release a series of chemicals that orchestrate the allergic reaction. Within every mast cell or basophil there are 500-1500 granules, which contain more than 30 different allergy-causing chemicals.

The most commonly known chemical released is histamine. Histamine causes itching if released in the skin, wheezing if released in the lungs, and contributes to a loss of blood pressure if released throughout the body. Leukotrienes and Cytokines are also released.

What is anaphylaxis?

A severe, life-threatening allergic reaction is called Anaphylaxis. It is a medical emergency and requires immediate treatment. It can cause an anaphylactic shock and must be treated with an adrenaline pen.

In most allergic reactions the resulting chemicals are released locally into the tissues in a particular part of the body so the symptoms of an allergic reaction only occur in this area.

In anaphylaxis, the chemicals that cause the allergic symptoms (e.g. histamine) are released into the bloodstream. The symptoms of anaphylaxis usually occur within minutes of exposure to the trigger substance (allergen) but sometimes an hour or so later.

When I have an anaphylactic reaction to egg I react within 10 seconds of swallowing. My oesophagus becomes dry and I start vomiting, then my airways start to constrict and I have difficulty breathing. Sophie (my sister) will be fine for an hour then she will get itchy, blotchy (with hives) and start to feel sleepy (due to a drop in blood pressure).

Allergy Tests

These help monitor and diagnose allergies as babies and children with certain food allergies often grow out of them over time. Or in my case get more severe as I get older.

There are 2 common types of allergy tests for food, plants and animals:

A blood test, IgE test or formally a RAST test. This is used to measure the number of IgE antibodies in your blood that have been produced by your immune system in response to a suspected allergen.

A skin prick test is usually the first test done when looking for an allergen and is used to monitor them.  Your skin is pricked with a tiny amount of the suspected allergen to see if there’s a reaction. If there is, the skin around the prick will very quickly become itchy and a red, swollen mark called a wheal will appear. After 10 minutes they measure the size of the wheal in mm. The larger the wheal the more severe the reaction.

A month ago, on I had my routine skin prick test to see how my allergies have developed from my last visit in 2013.

Positive control = histamine, Negative control = 50% glycerol (the same solution as what the allergens are made up of but without the allergen).

Tests included: House Dust mite, American house dust mite, Grass, Trees, Silver Birch, Cats, Dogs.  The most common molds people are allergic to are: Alternaria, Aspergillus, Cladosporium.  The doctor puts a drop of allergen solution (50% glycerol, liquid allergen and water) on the skin and then uses a lancet to prick the skin.


This is what the wheal for Egg and Raw Egg look like after 10 minutes.

To get the measurements you measure the width and length of the hive and add them together.

What is the advice?

This is the NHS advice for what to do if you think someone is experiencing anaphylaxis:




Know what triggers your anaphylactic reaction and avoid the triggers as much as possible. An allergy test will help diagnose these.

Watch out for symptoms, if you experience them take your EpiPen or epinephrine injection (adrenaline auto-injector) which should reduce swelling, wheezing and improve blood pressure within minutes. If you don’t improve take another injection in 5 minutes. Take no chances – Don’t hesitate to take adrenaline, Hesitation can result in deterioration and death. Call 999 as symptoms can re-occur later.


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