Asthma

Asthma is a chronic inflammatory disorder of the bronchioles characterised by recurrent respiratory symptoms and reversible airway obstruction. It is one of the most common long-term respiratory conditions worldwide and affects individuals of all ages. The disease is marked by periods of relative stability punctuated by episodic exacerbations, often triggered by environmental exposures or physiological stress. Asthma significantly contributes to global morbidity and, despite advances in management, remains a major public health concern.

Clinical Features and Symptomatology

Asthma presents with a range of respiratory symptoms that vary in frequency and intensity. The hallmark manifestations include wheezing, coughing, chest tightness, and shortness of breath. These occur due to bronchial hyperresponsiveness, airway inflammation, and episodic bronchoconstriction. Sputum production may accompany coughing, and during recovery from an exacerbation, sputum can appear purulent owing to increased eosinophils.
Symptoms frequently worsen at night or in the early hours of the morning, reflecting circadian variations in airway tone and inflammatory activity. Cold air, physical exertion, and exposure to respiratory irritants often trigger symptoms. While some individuals exhibit only occasional episodes in response to specific triggers, others experience persistent and readily provoked symptoms.
Exacerbations represent acute deteriorations in asthma control. These episodes involve pronounced narrowing of the bronchioles, increased mucus secretion, and reduced airflow to the alveoli. Common precipitants include inhaled allergens such as pollen, dust, or air pollutants. Exacerbations may occur multiple times per day or only intermittently, depending on individual susceptibility.

Associated Conditions

A range of comorbidities has been observed with notable frequency in people with asthma. Gastro-oesophageal reflux disease, rhinosinusitis, and obstructive sleep apnoea are particularly common. Psychological conditions, including anxiety and mood disorders, show an increased prevalence, though the direction of causality remains uncertain. Some studies indicate that current asthma is associated with increased all-cause and cardiovascular mortality.
Asthma, especially when severe or poorly controlled, is linked with the later development of chronic obstructive pulmonary disease, illustrating the continuum between obstructive lung disorders. Dental problems, including an increased risk of caries, may arise due to the reduced salivary flow associated with beta₂-adrenergic agonists. Conversely, certain asthma medications may lower susceptibility to dental erosion.

Aetiology and Contributing Factors

Asthma arises from a complex interaction between genetic predisposition and environmental exposures, with both influencing disease severity and therapeutic responsiveness. Cases beginning before the age of twelve are more often attributed to inherited factors, whereas adult-onset asthma tends to be associated with environmental influences.
A prominent theory explaining increasing global asthma rates is the role of epigenetic changes driven by modern lifestyle and environmental alterations. These heritable modifications, independent of underlying DNA sequence changes, are believed to shape immune and respiratory responses.

Environmental Influences

Numerous environmental factors contribute to asthma onset and exacerbation:

• Air pollution from traffic emissions, ozone, and other pollutants increases both the incidence and severity of asthma. Poor air quality disproportionately affects socioeconomically disadvantaged communities.
• Allergens, including dust mites, animal dander, cockroaches, moulds, and various airborne particles, have strong associations with sensitisation and symptom provocation.
• Occupational exposures to substances such as ammonia, latex, pesticides, wood dust, welding fumes, isocyanate paints, glutaraldehyde, and metalworking fluids can induce asthma; these agents are termed asthmagens.
• Indoor volatile organic compounds, such as formaldehyde, may contribute to asthma development, and phthalates in certain plastics have been linked to increased risk.
• Tobacco smoke exposure, both antenatal and postnatal, is associated with higher rates of asthma-like symptoms.
• Pesticides have been implicated, though definitive causal links remain under investigation.
• Gas stove emissions have been identified as a significant risk factor, contributing to a measurable fraction of cases in some populations.

Infections and the Hygiene Hypothesis

Respiratory viral infections in early life, particularly respiratory syncytial virus and rhinovirus, increase the likelihood of developing asthma. Conversely, the hygiene hypothesis proposes that reduced microbial exposure during childhood in highly sanitised environments may impair immune development, elevating the risk of atopic diseases. Evidence supporting this includes lower asthma rates in children raised on farms or in households with animals, and correlations with delivery by caesarean section due to reduced exposure to maternal microbiota.

Genetic Factors

Family history is a strong predictor of asthma, with numerous candidate genes implicated in immune regulation, airway responsiveness, and inflammatory pathways. The interplay between genetic susceptibility and environmental exposures determines individual risk profiles and patterns of disease expression.

Diagnosis and Classification

Diagnosis relies on recognising characteristic symptoms and confirming variable airflow limitation using spirometry. A reduced forced expiratory volume in one second (FEV₁) and reduced FEV₁/forced vital capacity ratio support the diagnosis, particularly when reversible with bronchodilator therapy. Peak expiratory flow monitoring assists in assessing variability.
Asthma severity is classified based on symptom frequency, nocturnal awakenings, need for rescue medication, and spirometric findings. Additionally, asthma may be categorised as atopic or non-atopic, depending on the presence of IgE-mediated hypersensitivity.

Management and Treatment

Although incurable, asthma is highly manageable with appropriate treatment strategies. Effective control aims to minimise symptoms, prevent exacerbations, and maintain optimal lung function.
Key management approaches include:

• Avoidance of triggers, such as allergens and respiratory irritants, where practical.
• Inhaled corticosteroids, the cornerstone of long-term anti-inflammatory therapy.
• Long-acting beta-adrenoceptor agonists (LABAs) or antileukotriene agents, used in combination with inhaled corticosteroids for persistent symptoms.
• Short-acting beta₂-adrenergic agonists, such as salbutamol, for rapid relief during acute attacks.
• Oral corticosteroids, and in severe cases intravenous corticosteroids or magnesium sulphate, for exacerbations requiring urgent intervention.

Hospitalisation may be necessary for life-threatening episodes.

Epidemiology and Historical Perspectives

Asthma affected roughly 262 million people globally in 2019 and caused over 460,000 deaths, the majority occurring in low-income countries. Childhood asthma is particularly prevalent, and worldwide rates have risen markedly since the mid-twentieth century.
Historically, asthma was recognised in ancient civilisations, including those of Egypt. The term itself derives from the Greek word for “panting”, reflecting the characteristic symptom of breathlessness described in early medical texts.