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.

There is currently no cure for asthma, but with proper treatment, it can be managed.

Breathing: Normal Airways Vs. Asthma Airways

Normal: In someone with optimal lung function, air is inhaled through the nose and mouth, passing through the trachea (windpipe) before moving into the bronchi (large airways). The bronchi branch into smaller tubes, ending in many small sacs called alveoli. It’s in the alveoli that oxygen is passed to the blood and carbon dioxide is removed.

Asthma: In someone with asthma, the airways are inflamed, and when triggered, can constrict even more, obstructing airflow to the lungs.

What are the symptoms?

Asthma can be different for everyone. Asthma symptoms can also vary over time, with few or no symptoms when asthma is well controlled. The common signs and symptoms of poorly controlled asthma include:

  • Shortness of breath
  • Regular coughing
  • Wheezing
  • Chest tightness
  • Increased mucus production
  • Trouble sleeping because of breathing difficulty
  • Being unable to take part in physical activities without breathing difficulty

These symptoms can occur slowly over hours or days, or they can come on as sudden, recurring attacks after which the symptoms can persist for some time before disappearing. If left untreated, asthma can cause permanent structural changes in your airways called – “airway remodelling,” – which is why it is important to get your asthma under control and keep treating it over the long term.

What is an asthma trigger?

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

  • Allergic trigger: cause allergic reactions. Allergic triggers include things like dust mites, pollens, moulds, pet dander,
  • Non-allergic trigger: are usually irritants. Non-allergic triggers include things like smoke, cold air, certain air pollutants, intense emotions

Learn more about different types of asthma triggers and how to manage them.

Who gets asthma?

Asthma affects more than 4.6 million people in Canada, including 900,000 children under the age of 19. In Canada, asthma is the third-most common chronic disease. Every day, over 300 Canadians are diagnosed with asthma, and tragically every year an estimated 250 Canadians die from an asthma attack.

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

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