Asthma is a chronic respiratory disorder characterised by variable respiratory symptoms and variable expiratory airflow limitation associated with airway inflammation and hyperresponsiveness. Symptoms commonly include wheezing, breathlessness, chest tightness and cough, with their intensity and timing varying between individuals and over time. Airways in Asthma can become narrowed because of contraction of airway smooth muscle, mucosal swelling, increased mucus production and inflammatory changes. The degree of airway narrowing can fluctuate, which distinguishes Asthma from diseases characterised by persistently fixed airflow limitation. Asthma can begin during childhood or adulthood and has multiple phenotypes and triggers rather than one universal cause.
Asthma involves complex interactions among airway epithelial cells, immune pathways, smooth muscle, mucus-producing cells and environmental exposures. Type 2 inflammation, involving pathways associated with cytokines such as interleukin-4, interleukin-5 and interleukin-13, is important in many forms of Asthma, particularly allergic and eosinophilic phenotypes. Other forms have different inflammatory profiles, and not every person with Asthma has prominent eosinophilic inflammation. Airway hyperresponsiveness means that the bronchi constrict excessively in response to stimuli that produce little or no obstruction in people without Asthma. Repeated inflammation can produce airway remodelling, including structural changes that may reduce reversibility over time.
Asthma triggers vary substantially among individuals. Common triggers include viral respiratory infections, allergens, exercise, cold air, smoke, air pollution and certain occupational exposures. Some people experience symptoms after exposure to particular medications, including aspirin or other non-steroidal anti-inflammatory drugs, while others have symptoms related to workplace chemicals or irritants. Emotional stress can influence symptoms but should not be treated as the fundamental cause of Asthma. Trigger avoidance can reduce exacerbations when a specific trigger is established, but excessive avoidance without evidence can unnecessarily restrict normal activities.
Diagnosis requires evidence of characteristic variable symptoms together with objective evidence of variable expiratory airflow limitation where feasible. Spirometry can demonstrate airflow obstruction, and improvement after bronchodilator administration can support the diagnosis. Peak expiratory flow monitoring over time can demonstrate variability in selected circumstances. Bronchial provocation testing may be used when routine tests do not establish the diagnosis but clinical suspicion remains. A normal test performed while symptoms are absent does not always exclude Asthma. Conversely, wheezing and breathlessness have many possible causes, including chronic obstructive pulmonary disease, heart disease, vocal-cord dysfunction, pulmonary embolism and anxiety-related hyperventilation.
Inhaled corticosteroids are central to modern Asthma management because they suppress airway inflammation and reduce the risk of exacerbations. Reliever medicines that relax airway smooth muscle can rapidly improve bronchoconstriction, but relying exclusively on short-acting bronchodilators without adequate anti-inflammatory treatment can leave the underlying inflammation insufficiently controlled. Depending on severity and treatment strategy, inhaled corticosteroids may be combined with long-acting bronchodilators, and some regimens use an inhaled corticosteroid-containing combination as both maintenance and reliever therapy. Treatment is adjusted according to symptom control, exacerbation risk, inhaler technique, adherence and response.
Inhaler technique is a major practical determinant of Asthma treatment effectiveness. Different inhalers have different requirements, and incorrect technique can result in much of the medicine depositing in the mouth or throat rather than reaching the lower airways. Spacers can improve delivery for suitable pressurised metered-dose inhalers and are particularly useful in some age groups. Regular review allows clinicians to check technique, adherence, trigger exposure, symptom frequency and exacerbation history. Asthma action plans can help people recognise worsening control and follow an agreed response strategy. Treatment should be stepped up or down according to sustained control and clinical assessment rather than changed solely because of one good or bad day.
Asthma exacerbations are episodes in which symptoms and airflow obstruction worsen beyond a person's usual variation. They can be triggered by viral infections, allergens, medication issues, pollution or other factors. Severe attacks can cause profound airflow limitation, exhaustion, hypoxaemia and, in extreme cases, respiratory failure. Warning signs include rapidly worsening breathlessness, difficulty speaking, markedly reduced peak flow when monitoring is appropriate, poor response to prescribed reliever treatment or increasing respiratory effort. Severe or rapidly deteriorating symptoms require urgent medical assessment. Asthma deaths are preventable in many circumstances through appropriate anti-inflammatory treatment, recognition of deterioration and access to emergency care, although severe disease can remain dangerous even with good management.
Common misconceptions include the belief that Asthma is purely an allergic condition, that people with Asthma should avoid exercise, or that being symptom-free means the underlying airway inflammation has necessarily disappeared. Exercise is generally beneficial and can be part of good respiratory conditioning, although some people have exercise-induced bronchoconstriction requiring appropriate management. Asthma also varies across the lifespan, and childhood symptoms do not always follow the same trajectory into adulthood.
Another misconception is that inhaled corticosteroids are equivalent to systemic steroids in terms of exposure and risk; inhaled treatment is designed to deliver anti-inflammatory medicine predominantly to the airways, although adverse effects remain possible. Accurate diagnosis, regular review and appropriate anti-inflammatory treatment are central to long-term Asthma control.
