How does asthma differ from COPD?

Both cause airflow obstruction, but asthma's obstruction is typically variable and largely reversible and driven by airway inflammation and hyperresponsiveness, whereas COPD's obstruction is usually persistent and only partly reversible and linked to structural lung damage from chronic inhaled exposures; the two can also overlap.

What does 'variable airflow limitation' mean in asthma?

It means the degree of airway narrowing changes over time — worsening during exacerbations or in response to triggers and improving spontaneously or with treatment — which objective tests can demonstrate as variability in lung function such as the FEV1.

Asthma

Asthma is a common chronic inflammatory disorder of the airways characterised by variable respiratory symptoms — wheeze, breathlessness, chest tightness, and cough — together with variable expiratory airflow limitation. Its hallmark is reversibility: the airflow obstruction and symptoms fluctuate over time and in intensity, often improving spontaneously or with treatment, and the airways are typically hyperresponsive to a range of triggers.

Definition

Asthma is a heterogeneous disease, usually characterised by chronic airway inflammation, defined by a history of respiratory symptoms such as wheeze, shortness of breath, chest tightness, and cough that vary over time and in intensity, together with variable expiratory airflow limitation and bronchial hyperresponsiveness.

Scope

This entry covers the definition of asthma, its underlying airway inflammation and hyperresponsiveness, the concept of variable and reversible airflow limitation, recognised triggers and phenotypes, and the role of objective tests of variability. It treats asthma as a clinical and methodological topic and does not provide dosing, individualized diagnosis, or treatment recommendations.

Key concepts

Variable, reversible airflow limitation
Chronic airway inflammation
Bronchial (airway) hyperresponsiveness
Type 2 (eosinophilic/allergic) inflammation
Airway remodelling
Triggers (allergens, exercise, infection, irritants)
Asthma phenotypes and endotypes
Exacerbations

Mechanisms

In most patients the airways show chronic inflammation in which immune cells — frequently eosinophils and T-helper-2 lymphocytes in the so-called type 2 pattern — release mediators that drive airway smooth-muscle contraction, mucosal oedema, and mucus secretion. This produces episodic narrowing that limits expiratory airflow but is characteristically reversible, and it renders the airways hyperresponsive, so that stimuli such as allergens, exercise, cold air, or viral infection provoke exaggerated bronchoconstriction. Over time, persistent inflammation can lead to structural airway remodelling. Asthma is increasingly understood as a collection of phenotypes and endotypes — for example type-2-high versus type-2-low inflammation — which has underpinned targeted biologic therapies for severe disease.

Clinical relevance

Asthma is one of the most prevalent chronic diseases and a major source of respiratory symptoms across all ages, so its definition and natural history inform how respiratory evidence is read and appraised. This entry is a reference for what asthma is and how it is conceptualised; it is descriptive and is not a basis for individual diagnosis or treatment decisions.

Epidemiology

Asthma affects an estimated several hundred million people worldwide across children and adults, making it one of the most common chronic respiratory conditions; prevalence varies widely between regions and has risen in many populations, and a substantial minority of patients have severe disease that accounts for a disproportionate share of morbidity.

History

Recognised since antiquity as episodic breathlessness, asthma was long understood chiefly as a disorder of bronchospasm. Twentieth-century work reframed it as fundamentally an inflammatory disease of the airways, a shift that explained airway hyperresponsiveness and variability and reoriented the field; more recently, the recognition of distinct inflammatory phenotypes and endotypes has further refined the concept.

Debates

Is asthma one disease or many?: Asthma is increasingly viewed not as a single entity but as an umbrella of phenotypes and endotypes with differing inflammatory mechanisms, which has implications for how it is defined, studied, and targeted by therapy.

Seminal works

fanta-2009
papi-2018

Frequently asked questions

How does asthma differ from COPD?: Both cause airflow obstruction, but asthma's obstruction is typically variable and largely reversible and driven by airway inflammation and hyperresponsiveness, whereas COPD's obstruction is usually persistent and only partly reversible and linked to structural lung damage from chronic inhaled exposures; the two can also overlap.
What does 'variable airflow limitation' mean in asthma?: It means the degree of airway narrowing changes over time — worsening during exacerbations or in response to triggers and improving spontaneously or with treatment — which objective tests can demonstrate as variability in lung function such as the FEV1.