Emergent Care / Stabilization:
For emergency management, see acute exacerbation of asthma.

Diagnosis Overview:
Asthma is a heterogeneous disease characterized by chronic inflammation, variable airway obstruction, and hyperresponsiveness leading to cough, wheezing, shortness of breath, and chest tightness. The pathophysiology of asthma is complex and results from the interplay of immune system dysregulation, genetic predisposition, and environmental triggers. In the past few years, a better classification of asthma phenotypes and underlying endotypes has led to more precise diagnostic criteria and tailored therapeutic plans. While a chronic condition, asthma is generally an intermittent disease with acute exacerbations interspersed with symptom-free periods. In severe cases, some patients may experience symptoms of airway obstruction daily.

An estimated 26 million people in the United States have asthma (19 million adults and 7 million children). Recent epidemiological analyses of the Centers for Disease Control and Prevention (CDC) National Health and Nutrition Examination Survey (NHANES) data show that females comprise about 64% of adult asthma cases and are 1.76 times more likely to have asthma than males. This female predominance tends to emerge after puberty. While asthma can occur at any age, it most commonly presents in childhood or adolescence, with a second peak of incidence in middle-aged adults. Childhood-onset asthma persists into adulthood in about 40%-60% of cases. Risk factors for asthma include heredity, viral infections in the first 3 years of life, exposure to tobacco smoke, and socioeconomic factors such as access to medical care, rodent / cockroach infestation, and income level.

Asthma pathophysiology is driven by chronic airway inflammation and hyperresponsiveness with distinct clinical and molecular phenotypes: type 2 (Th2 / ILC2-driven) asthma is characterized by eosinophilic inflammation, elevated interleukins (IL-4, IL-5, and IL-13), immunoglobulin E (IgE) production, and airway remodeling, and is typically responsive to corticosteroids and targeted biologics. Type 2 asthma predominates in children and allergic adults. In contrast, non-type 2 asthma features neutrophilic and paucigranulocytic onset and elevations in IL-17, interferon-gamma, and tumor necrosis factor (TNF)-alpha; it is often associated with obesity, adult onset, and poor response to standard therapies.

Asthma presents with characteristic symptoms including wheezing, shortness of breath, cough, and chest tightness that typically worsens at night or early morning, varies in intensity over time, and is often triggered by viral infections, exercise, allergen exposure, and weather changes. The American Academy of Family Physicians, as outlined in the Global Initiative for Asthma (GINA) guidelines, recommends confirming the diagnosis with pulmonary function testing to demonstrate variable airflow limitation (specifically, a change in FEV₁ of more than 12% and 200 mL from baseline or a peak expiratory flow change of at least 20%) and advises against relying solely on symptoms in order to avoid misdiagnosis and overtreatment; bronchial provocation testing may be considered in select cases with normal spirometry but persistent symptoms, and atopy increases the likelihood of allergic asthma but is not required for diagnosis.

Adults with asthma often experience accelerated loss of lung function compared to adults without asthma, but the clinical significance of this and the extent to which these decline contribute to the development of fixed airflow obstruction are unknown.

Exacerbation is a term used to describe either a brief symptom flare relieved by short-acting beta2 agonists or a more prolonged decline in lung function with increased symptoms, often triggered by allergens or viral infections, that may require escalation of anti-inflammatory therapy.