Asthma is an inflammatory condition of the lungs, affecting 5.4 million people in the UK.1 It narrows the airways making it difficult to breathe and is characterised by repeated exacerbations or attacks.

Asthma is classed as severe or difficult to control if the symptoms remain uncontrolled even when you are prescribed the highest dose of ICS (inhaled corticosteroids – brown inhaler) and take your medications correctly.2

Asthma episodes or attacks and related symptoms


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Icon representing wheezing




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Shortness of breath


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Chest tightness



Allergic asthma is the most common type of asthma and it is caused by the immune system.3

Normally, the immune system protects you from diseases – it reacts to potentially dangerous substances, like viruses or bacteria, and makes them harmless.

Allergies and allergic reactions happen when your immune system overreacts when exposed to common substances.

This can occur in response to triggers such as:


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Dust mites


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Animal hair


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Mould spores



In allergic asthma, this causes a reaction that worsens the symptoms of asthma.

What is severe allergic asthma?

If you have allergic asthma, and your symptoms are uncontrolled despite medication and being prescribed the highest dose of ICS (inhaled corticosteroids – brown inhaler), this will be classed as severe allergic asthma.

Inside the airway

Special proteins called immunoglobulin E (IgE) play an important role in allergic asthma.4

IgE acts like a ‘radar’ for allergens; when there is an allergen present, it is detected by the IgE protein, which triggers an allergic reaction.

  • IgE binds to an allergen, driving the actions of other parts of the immune system
  • When the IgE is already attached to a specific cell called ‘mast cells’, the binding of the allergens to the IgE activates the mast cell. These cells act as gatekeepers for the immune system and are found in large numbers in the skin, in the lining of the airways and in the gut
    • Mast cells store histamine and other powerful chemicals involved in inflammation
  • When IgE on mast cells is activated by an allergen, powerful chemicals such as histamine are released from the mast cell
  • This leads to an inflammatory reaction:
    • Airways become red, swollen and tight
    • Mucus is released
    • It also creates the wheezing, coughing, and shortness of breath associated with an asthma attack


no 1


Allergens in the airways bind to IgE present on mast cells


no 2


When IgE on mast cells is activated by an allergen, powerful chemicals such as histamine are released

no 3


This leads to an inflammatory reaction


Cellular level diagram showing how allergens in the airways cause an inflammatory reactionkey


  1. Asthma UK. Living in Limbo: The Scale of Unmet Need in Difficult and Severe Asthma. Available online at: https://www.asthma.org.uk/69841483/globalassets/get-involved/external-af... [Accessed February 2022].
  2. Asthma UK. What is severe asthma? Available online at: https://www.asthma.org.uk/advice/severe-asthma/what-is-severe-asthma/. [Accessed February 2022].
  3. Center for Allergy & Asthma of Georgia. 4 Most Common Types of Asthma. Available online at: https://www.caageorgia.com/about-us/blog/2019/november/4-most-common-typ.... [Accessed February 2022].
  4. Owen CE. Pharmacology & Therapeutics 2007,113(1):121–133.


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UK | February 2022 | 184169

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