What is asthma?

Asthma is a chronic inflammatory disease of the airways that causes symptoms like shortness of breath, chest tightness, coughing, and wheezing. Asthma causes inflammation and narrowing of the bronchial tubes, which leads to limited airflow and difficulty breathing.

The airways of our lungs are surrounded by muscles and contain mucous glands. These muscles are normally relaxed, but if you have asthma, they are often sensitive and inflamed.

When people with asthma encounter triggers, these muscles react by tightening even more, the lining of the airways swell and the airways can fill up with mucus. This makes breathing very difficult and leads to asthma symptoms or asthma exacerbation, also known as an asthma attack.


What is an asthma trigger?

A trigger is anything that irritates your airways. Asthma is caused by two types of triggers. 

  • Allergic trigger: caused by inflammatory triggers such as dust mites, pollens, moulds, pet dander, viral infections
  • Non-allergic trigger: triggered by smoke, exercise, cold air, certain air pollutants, intense emotions

Who gets asthma?

Asthma affects about 3.8 million Canadians, including 850,000 children under the age of 14. In Canada, asthma is the third-most common chronic disease. Every day, over 300 Canadians are diagnosed with asthma. Every week, four Canadians die from an asthma attack.

Asthma is not contagious. Its cause is still unknown, but researchers have determined that asthma can be caused by both hereditary and inherited factors.

Just because you have a parent with asthma (or an allergy) does not mean you will have it, too. If one or both of your parents has asthma and/or allergies, it’s more likely that you will develop them. Researchers aren’t yet sure exactly why this is.

Why do people get asthma?

Research has yet to show a definitive cause of asthma. However, researchers have determined several risk factors that can lead to asthma development.

Family History and Genetics

Children of mothers with asthma are three times more likely to suffer from asthma, and 2.5 times more likely if the father has asthma. More than 30 genes have been linked to asthma so far, and gene-gene interactions, gene-environment interactions and epigenetic modifications also play a part. Genetic differences also play a role in differences in response to treatment.


People are more likely to have asthma if they have certain types of allergies, such ones which can affect the eyes and nose. However, not everyone who has allergies will get asthma and not everyone who has asthma is affected by allergies. Respiratory allergies and some types of asthma are related to an antibody called immunoglobulin E (IgE), which the immune system produces in response to allergens. To protect the body, the IgE causes allergic reactions that can affect the eyes, nose, throat, lungs and skin.

Premature Birth

Children born before 37 weeks are at increased risk of developing asthma later in life.

Lung Infections

Babies or small children may be at risk of developing asthma later in life if they had certain lung infections at a very early age.

Occupational Exposures

There are more than 200 substances including gases, dust participles and chemical fumes and vapours that can cause asthma in the workplace. This type of asthma is known as occupational asthma, and is a common cause of adult onset asthma.


Women can develop adult-onset asthma during or after menopause.

Environment Air Quality

Smoking, exhaust fumes and airborne particulate matter can be linked to causing asthma. 


Extra weight around the chest might squeeze the lungs and make it more difficult to inhale. Fat tissue produces inflammatory substances that might influence the lungs and affect asthma.