What is Severe Asthma?

Though patients with mild-to-moderate asthma can experience difficulty breathing, it is especially difficult for those with Severe Asthma where symptoms can be life-threatening. In either case, patients can’t participate in daily activities if their disease is uncontrolled.

Similar to those with mild–moderate asthma, patients with Severe Asthma also have disease that is chronic. However, they have more difficulty achieving control of their disease, and need a greater number of medications and often at higher doses. They require more medical care than patients with mild-to-moderate disease.

How is Severe Asthma diagnosed?

More steps are taken to arrive at a diagnosis of Severe Asthma compared to mild-to-moderate asthma. As in mild-to-moderate asthma, healthcare providers will take a detailed medical history, listen for wheezing on examination of the chest, and assess for underlying allergic and non-allergic triggers. Underlying diseases such as eczema or allergic rhinitis may be clues that allergy is present. Allergy skin testing may be performed to evaluate if specific allergic triggers are present that can result in asthma attacks.

In addition, healthcare professionals will likely also conduct objective examinations of lung function including spirometry, or peak expiratory flow (how fast a person can exhale starting from full inhalation), and in some cases, sputum cell counts, which indicate the presence, type, and extent of inflammation in the airways. These objective tests in addition to history will help determine if a patient has Severe Asthma, and will inform treatment choices for patients. 

Healthcare providers should refer patients with Severe Asthma to a specialist to confirm their diagnosis and assist in management.

How common is Severe Asthma?

It is estimated that as many as 230,000-465,000 Canadians suffer from Severe Asthma, approximately 5-10% of the general asthma population. Fatalities are higher in this group compared to patients with mild-to-moderate disease. Each year, over 250 Canadians die from asthma. Globally, over 450,000 patients with asthma die prematurely on an annual basis because of their condition.

How is Severe Asthma treated and managed?

Like patients with mild-to-moderate asthma, patients with Severe Asthma should try to minimize their exposure to triggers, both allergic and non-allergic, that exacerbate their asthma.

Similar to mild-to-moderate asthma, patients with Severe Asthma take inhaled medications to control the underlying inflammation in their airways, and medications that relax the muscles around the airways and treat symptoms like wheezing, coughing, or shortness of breath.

Unlike patients with mild-to-moderate asthma, patients with severe disease may be required to take oral corticosteroids in addition to their inhaled corticosteroids to provide additional control of the inflammation in their airways.

There has been a search for alternative treatments to oral corticosteroids because their long-term use is associated with side effects, including weight gain which can make asthma worse. Other side effects associated with long-term use of oral corticosteroids include the development of cataracts, osteoporosis, and elevated blood sugar that can trigger diabetes. In a study including 808 people with Severe Asthma, it was found that 93% of them had one or more conditions linked to their oral corticosteroid use including Type II diabetes, osteoporosis, dyspeptic disorders, and cataracts.

Research is shedding light on the sub-types of asthma or “phenotypes”. Severe Asthma can be eosinophilic. Eosinophils are a type of white blood cell which are part of the body’s immune system. For about 40% of patients with Severe Asthma, eosinophils drive their asthma, and oral/inhaled corticosteroids have been the mainstay of treatment.

Identifying the subtype of asthma that a patient has, for example, eosinophilic, presents an opportunity for precision medicine through biologic therapy. As an example, the biologic therapy omalizumab that is approved for asthma is effective in allergic eosinophilic asthma.

Medications called biologics, many of which are taken by injection, offer the possibility of controlling Severe Asthma and may be an alternative to oral corticosteroids. Some of the biologics that are available in Canada to treat Severe Asthma include dupilumab, tezepelumab, omalizumab, reslizumab, mepolizumab and benralizumab. The biologics carry a higher price tag than standard asthma medications: the annual cost of these medications in Canada ranges from just under $8,000 for a patient receiving one vial monthly to more than $47,000 for a patient receiving three vials every two weeks, according to the Canadian Agency for Drugs and Technologies in Health.

It is a goal of asthma care to empower patients with asthma to manage their disease. Accordingly, personalized Asthma Action Plans are instrumental for optimal self-management of this chronic condition.

What are the differences between mild-to-moderate asthma and Severe Asthma?

Patients who have mild-to-moderate asthma can generally control their disease with commonly prescribed medications. But patients with more severe illness, who are on high doses of medications including oral corticosteroids, still may find themselves visiting hospital emergency rooms because of an asthma attack and unable to control their disease. They may find that they have to typically adjust their daily lives, be it missing work, missing school, or not participating in physical activities. The asthma attacks experienced by patients with Severe Asthma may even result in death.

Patients with Severe Asthma are more reliant on their asthma medications. A cross-Canada survey conducted by Asthma Canada looking at the impact of Severe Asthma found that the majority of respondents (83.5%) said they use their controller medication once a day, and about seven out of every 10 said they use it at least twice a day. A significant portion (42.2%) of respondents with Severe Asthma said they use their reliever medication once a day, and 28.8% said they use it at least twice daily.

One of the other differences between mild-to-moderate asthma and Severe Asthma is that patients with severe disease are more likely to have co-morbidities or co-existing medical conditions. These include obesity, obstructive sleep apnea, and gastroesophageal reflux disease (reflux of stomach contents into the esophagus).

What are the economic and social burdens in Canada related to Severe Asthma?

Severe Asthma takes a serious toll on patients and on Canada’s healthcare system. Patients with Severe Asthma will often need more medical care and will be visiting hospital emergency rooms, and visiting their family doctors and specialists. In 2021, asthma attacks led to more than 80,000 visits to emergency rooms in Canada. The cost of asthma to the Canadian economy is expected to climb to $4.2 billion by 2030.

According to one study, children with Severe Asthma were more likely (9.1%) to miss seven days or more of school than children with mild (5.7%) or moderate disease (5.3%).

In terms of a social burden, Severe Asthma as a chronic condition impairs an individual’s ability not only to breathe but to work and live a happy and healthy life. With increased disease severity, a patient’s quality of life becomes progressively worse. Sadly, depression is a co-morbidity that occurs with Severe Asthma.

Severe Asthma Patient Charter

This charter includes 6 guiding principles for people with Severe Asthma and what they should expect for the management of this chronic disease.


Biologics are a new type of asthma medication used to help people living with Severe Asthma gain long-term control of their asthma symptoms. Learn about this treatment option.

Asthma & Allergy HelpLine

Have questions about Severe Asthma? Contact our free HelpLine to be connected to a Certified Respiratory Educator for personalized support.

Asthma & Nasal Polyps

Biologics are a new type of asthma medication used to help people living with Severe Asthma gain long-term control of their asthma symptoms. Learn about this treatment option.

Define Your Asthma: A Guide for People Living with Severe Asthma

Developed thanks to a global community sharing their experiences, advice and tips to help others.

Severe Asthma: The Canadian Patient Journey

Download a copy of our study which revealed the social, financial and health impacts of Severe Asthma on the lives of Canadians. This landmark study is now used to educate, raise awareness and advocate on behalf of Canadians with Severe Asthma.  [Click here to download in French].