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Definition

Severe Asthma Definition

The ERS/ATS International Severe Asthma Guidelines defines severe asthma as asthma that is still uncontrolled despite good adherence with high-dose ICS-LABA and management of contributory factors, or if the patient needs high dose ICS-LABA to maintain good asthma control (GINA, 2025). Severe asthma is a heterogeneous condition consisting of phenotypes such as eosinophilic asthma (Chung et al, 2014). In these guidelines, the definition of “uncontrolled” asthma includes persistent symptoms, frequent or severe exacerbations, and/or low lung function.

Severe Asthma is Asthma that remains...

Uncontrolled...

Despite treatable factors having been addressed...

And maximal inhaled therapy being taken regularly

Uncontrolled...

Poor symptom control
Frequent severe exacerbations / flare-ups / attacks
Serious exacerbations (e.g. hospitalisation, ICU stay or mechanical ventilation)
Airflow limitation or
Controlled asthma that worsens on tapering of corticosteroid treatment

Despite treatable factors having been addressed...

Treatment adherence
Inhaler device technique
Self-monitoring
Trigger avoidance
Comorbidities identified and managed

And maximal inhaled therapy being taken regularly

High-dose inhaled corticosteroids (ICS) (e.g. beclomethasone >1000 mcg, budesonide >800mcg ) AND
Long-acting beta agonists (LABA) or other controller

Having severe asthma symptoms does not necessarily mean that the person has “severe asthma”. To explain this, it is important to understand two key concepts in asthma management: asthma control and asthma severity.

Asthma Control

ASTHMA CONTROL means the extent to which the features of asthma have been reduced or removed. There are two components:

‘symptom control’, meaning how often the person has symptoms, night waking and limited activity due to asthma
the person’s risk of having adverse outcomes in the future, particularly asthma flare-ups, accelerated decline in lung function, or medication side-effects.

Well-controlled asthma means that asthma symptoms are infrequent (twice a week or less), there is no night waking due to asthma, no limitation of normal activities, and the person is at a low risk of flare-ups.

Uncontrolled asthma, as well as burdening the patient with symptoms, can result in frequent flare-ups / attacks, adverse reactions to medication and chronic morbidity. In Australia, about 45% of adults with asthma have uncontrolled symptoms, and around one quarter have had a flare-up in the past year (Reddel et al. 2015). Risk factors such as past exacerbations, T2 biomarkers, and lifestyle factors can increase a patient’s chance of flare-ups/asthma attacks, even if they have few symptoms (McDonald et al, 2019, Meulmeester et al. 2025)

Asthma Severity

ASTHMA SEVERITY does not mean how bad the asthma symptoms are, but how much treatment is needed to keep asthma well-controlled.

Mild asthma is asthma that can be well-controlled with a low-dose maintenance inhaler therapy.

Severe asthma (also called ‘severe refractory asthma’) is asthma that remains uncontrolled (symptoms and/or flare-ups) despite treatable factors having been addressed and maximal inhaled therapy being taken, or, in a few patients, remains well-controlled only while high dose treatment is being taken. ‘Refractory’ means that the person’s asthma does not respond as well to treatment as it does for most people. For more information, see Diagnosis.

For strategic reasons in developing countries, the World Health Organisation (WHO) defines an additional category called “untreated severe asthma”. This refers to people with severe symptoms resulting from undiagnosed asthma, or unavailability of treatments (Bousquet et al. 2010). When inhaled corticosteroids are made available, asthma morbidity is dramatically reduced (GINA. 2024, Cerci Neto et al. 2008).

Most people with asthma experience mild to moderate symptoms, and most can respond well to standard maintenance inhaler therapy (inhaled corticosteroids with or without long-acting beta₂-agonists (LABAs)). However, some people continue to experience poor symptom control or asthma attacks, despite being prescribed maximum doses of maintenance inhaler therapy medication. This is called ‘difficult-to-treat asthma’. For many of these patients, this is because of problems that can be treated, including not using their maintenance inhaler therapy correctly or not taking it regularly, or because they also have other conditions such as sinusitis or obesity (called ‘comorbidities’) that can make asthma symptoms worse. Sometimes, it is because they don’t have asthma, but their respiratory symptoms are due to another condition such as cardiac disease or vocal cord dysfunction.

Within the clinic, it can be difficult to differentiate between these patient subsets (particularly difficult-to-treat and treatment-refractory). It is important to recognise that differences exist, as symptoms may result from differing underlying causes, which in turn require different intervention approaches. For more information, see Diagnosis.