Allergic asthma is the most common type of asthma.1 It usually starts in childhood. Nearly 25% of children with allergic asthma also have symptoms as adults.2 People with allergic asthma often have other allergic diseases such as eczema, hay fever (allergic rhinitis), or food and drug allergies.3 Allergic asthma ranges from mild to severe.1 It is usually the most severe for adults who have had it since childhood and people who are diagnosed with it as adults. These people are likely to have more frequent and severe asthma attacks.
What causes allergic asthma?
Allergic asthma tends to run in families.1 This means that genetics probably play a role in whether you have asthma and allergies.
The symptoms of asthma are wheezing, coughing, shortness of breath, and chest tightness.3 In a person with allergic asthma, these symptoms start after inhaling an allergen. Allergens are substances that are usually harmless, such as pet dander, pollen, and dust mites. In people with allergies, these allergens set off the immune system.
What happens when allergens set off the immune system?
In order to understand your lab results and medications, it is helpful to know what happens during an allergic reaction.
When an allergen triggers the immune system, many different kinds of cells and signaling chemicals get involved. The allergen enters the airway and turns on ‘mast cells’ and ‘dendritic cells’.4 These cells tell ‘type 2 helper (abbreviated Th2) cells’ to send out signaling chemicals called ‘interleukins’. There are different kinds of interleukins (abbreviated IL). Some examples are IL-4, IL-5, or IL-13.
Each interleukin has a different role in allergic asthma:
- IL-4 and IL-13 are signals to make an antibody called IgE (immunoglobulin E). IgE is responsible for many allergy symptoms, such as wheezing, coughing, swelling, itching, and runny nose.5,6
- IL-13 has a role in airway narrowing.4
- IL-5 and IL-13 increase the number of the eosinophils. Eosinophils are a type of white blood cell. People with asthma often have high levels of eosinophils.
Constant exposure to an allergen leads to ongoing inflammation.2 Ongoing inflammation may cause structural changes in the airways. Overtime, the airways may become more sensitive to allergens and irritants. They may not open as wide, even after treatment with medication.
How is allergic asthma diagnosed?
Asthma is diagnosed based on symptoms, a physical examination, and spirometry.5
Laboratory and additional lung function tests for people with allergic asthma often show:1
- High levels of exhaled nitric oxide (abbreviated FeNO)
- High levels of eosinophils
- Positive skin prick allergy tests or specific IgE blood tests
How is allergic asthma treated?
Inhaled corticosteroids can control symptoms for many people with allergic asthma.3 Corticosteroids quiet the signals from the Th2 cells and reduce inflammation.1
For adults and children older than five years who still have symptoms while taking an inhaled corticosteroid, a higher dose of inhaled corticosteroids or a second medication may be needed.5 The second medication is often a long-acting beta-agonist or a leukotriene agonist.
Some people with severe allergic asthma do not respond well to corticosteroids.7 For adults, health care providers may recommend the addition of a medication that blocks IgE.5,7