Asthma

Asthma is a chronic inflammatory disease of the airways that affects approximately 1 in 5 children and 1 in 10 adults in Singapore -- making it one of the most prevalent chronic conditions in the country. Properly understood and properly treated, asthma does not have to limit your life. Poorly managed, it can be both debilitating and, in severe attacks, life-threatening.

The goal of modern asthma management -- guided by the GINA (Global Initiative for Asthma) framework -- is not merely to reduce symptoms. It is to achieve full asthma control: no daytime symptoms, no night waking, no activity limitation, and reliever use less than twice a week. For most patients, with the right treatment, this is achievable.

What is Asthma?

Asthma is a chronic inflammatory condition affecting the airways -- the bronchi and bronchioles that carry air to and from the lung tissue. Three mechanisms underlie the airflow obstruction characteristic of asthma:

• Airway inflammation: The bronchial mucosa is chronically inflamed, even between symptomatic episodes. Eosinophils, mast cells, and T lymphocytes are the primary inflammatory cells involved in most forms of asthma.
• Bronchospasm: The smooth muscle surrounding the airway contracts in response to triggers, narrowing the airway lumen
• Mucus hypersecretion: Excess mucus production further obstructs airflow and contributes to cough

Crucially, the airflow obstruction in asthma is variable -- it fluctuates over time and reverses (either spontaneously or with treatment). This variability is both a defining characteristic of asthma and a key feature used in its diagnosis. Fixed airflow obstruction that does not reverse with bronchodilator is more characteristic of COPD.

Over years of uncontrolled inflammation, the airway wall undergoes structural remodelling -- thickening, collagen deposition, and smooth muscle hypertrophy that progressively reduces the airway diameter and leads to irreversible lung function decline. This is one of the most compelling arguments for treating asthma adequately from the outset rather than managing it reactively.

Asthma in Singapore: A Different Context

Asthma in Singapore has features that distinguish it from asthma in temperate countries, and these shape how it should be managed:

• House dust mites (HDM) are the dominant allergen. Singapore's warm, humid year-round climate creates ideal conditions for Dermatophagoides pteronyssinus and D. farinae to proliferate in bedding, carpets, and soft furnishings. Unlike seasonal hay fever in temperate countries, asthma triggered by HDM in Singapore is perennial -- present every day of the year.
• Haze from regional forest fires is a recurring trigger. Smoke particles from Indonesia and Malaysia reach Singapore periodically, causing acute spikes in air pollution that trigger asthma attacks. Patients with asthma should have a haze action plan in addition to their standard asthma action plan.
• Cockroach allergen is a significant indoor trigger in Singapore's urban housing environment, alongside HDM.
• Viral respiratory infections are the most common precipitant of asthma exacerbations in children. COVID-19 infection has added to this burden.
• Rhinitis-asthma overlap is common -- the majority of Singaporean patients with asthma also have allergic rhinitis, and treating rhinitis effectively improves asthma control.

Types of Asthma

Asthma is not a single disease -- it encompasses several clinically distinct subtypes (phenotypes) that differ in their underlying mechanism, triggers, patient demographics, and response to treatment. Identifying the correct phenotype guides targeted therapy.

• Allergic Asthma: The most common phenotype, particularly in Singapore. Triggered by inhaled allergens -- house dust mites (the dominant trigger in Singapore's humid climate), pet dander, mould. Often begins in childhood. Associated with elevated IgE, positive allergy skin tests, and frequently coexistent allergic rhinitis. Responds well to inhaled corticosteroids.
• Non-Allergic Asthma: Triggered by non-immunological mechanisms -- cold air, exercise, respiratory infections, irritants, strong odours. Normal IgE and negative allergy tests. More common in adult-onset asthma. May be associated with obesity, aspirin sensitivity (Samter's triad), or hormonal changes.
• Eosinophilic Asthma: Characterised by high eosinophil counts in blood and sputum. Often adult-onset, non-allergic, severe, and steroid-responsive. Elevated exhaled nitric oxide (FeNO) is a marker. Subset of severe eosinophilic asthma responds dramatically to biologic therapies (mepolizumab, benralizumab, dupilumab) targeting the eosinophilic pathway.
• Occupational Asthma: Caused or exacerbated by workplace exposures -- sensitisers (flour, latex, animal proteins) or irritants (chlorine, acids, isocyanates). Characteristic pattern: symptoms better on weekends and holidays, worse on return to work. Requires identification and elimination of the causative exposure. Common occupations: bakers, healthcare workers, painters, hairdressers.
• Exercise-induced Bronchoconstriction: Airway narrowing triggered by sustained exercise, particularly in cold or dry air. May occur as an isolated condition or alongside allergic asthma. Typically peaks 5-15 minutes after exercise stops and resolves within 30-60 minutes. Managed with pre-exercise SABA, regular ICS for persistent cases, or LTRA.
• Aspirin-Exacerbated Respiratory Disease: A triad of asthma, chronic rhinosinusitis with nasal polyps, and sensitivity to aspirin and NSAIDs. COX-1 inhibition diverts arachidonic acid to the leukotriene pathway, precipitating bronchoconstriction. Managed with leukotriene receptor antagonists and aspirin desensitisation in selected patients.

Symptoms of Asthma

Asthma symptoms are caused by airway narrowing and are characteristically variable -- they fluctuate over time, worsen with triggers, and improve with treatment or between episodes.

Classic symptoms

• Wheezing: A high-pitched whistling sound during breathing, most prominent on expiration
• Shortness of breath: A sensation of difficulty breathing or inability to take a full breath
• Chest tightness: A feeling of pressure, heaviness, or constriction in the chest
• Cough: Often dry and persistent; may be the only symptom in cough-variant asthma; typically worse at night or early morning

Patterns suggesting asthma rather than other diagnoses

• Symptoms that worsen at night or on waking is a hallmark of asthma physiology
• Symptoms triggered by specific exposures: allergens, cold air, exercise, respiratory infections
• Symptoms that vary: Symptoms may be better on some days than others, better on holiday, better away from work
• Symptoms that improve with a bronchodilator inhaler
• A history of childhood asthma or eczema, or a family history of asthma or allergy

Recognising an asthma attack

An asthma attack (exacerbation) is a worsening of symptoms beyond the patient's usual baseline. Severity is assessed by the degree of breathlessness, respiratory rate, ability to speak, and oxygen saturation.

• Mild attack: Increased symptoms, slight breathlessness, reliever inhaler provides relief within 15-20 minutes
• Moderate attack: Breathlessness interfering with normal activity, partially responsive to reliever
• Severe attack: Breathlessness so severe that speaking in full sentences is difficult; reliever not providing adequate relief/li>
• Life-threatening attack: silent chest (no wheeze due to minimal airflow), exhaustion, cyanosis (blue lips/fingertips), confusion

What Triggers Asthma?

Asthma triggers are substances or situations that provoke airway inflammation or bronchospasm in susceptible individuals. Identifying and managing a patient's specific triggers is an important component of asthma management.

Allergen triggers

• House dust mites: The primary trigger in Singapore; found in mattresses, pillows, carpets, and soft furnishings
• Cockroach allergen: Common in urban Singapore housing
• Pet dander: Cat (Fel d 1) and dog proteins; highly potent sensitisers
• Mould and fungal spores -- prevalent in Singapore's humid indoor environments

Environmental and Physical Triggers

• Viral respiratory infections: Rhinovirus, influenza, RSV, and COVID-19
• Air pollution and haze: PM2.5, nitrogen dioxide, ozone
• Tobacco smoke: Both active smoking and secondhand smoke
• Cold air and changes in weather
• Exercise: Particularly sustained aerobic activity in cold or dry air
• Strong odours: Perfumes, cleaning products, paint fumes
• Aspirin and NSAIDs: In aspirin-exacerbated respiratory disease
• Occupational exposures: Chemicals, dusts, biological agents

Physiological triggers

• Emotional stress: Activates the hypothalamic-pituitary axis and increases airway reactivity
• Gastro-esophageal reflux (GERD): Acid reflux can trigger bronchospasm via neural reflexes or microaspiration
• Hormonal changes: Premenstrual worsening of asthma is recognised in some women

The Connection Between Asthma and Allergic Rhinitis

Asthma and allergic rhinitis (nasal allergy) are closely connected -- they share the same mucosal lining, the same allergic inflammatory mechanism, and in Singapore, the same primary trigger (house dust mite). This relationship is so well established that the concept of 'one airway, one disease' now underpins guideline recommendations.

• Up to 80% of patients with asthma have allergic rhinitis, and untreated rhinitis significantly worsens asthma control
• Treating rhinitis effectively -- with intranasal corticosteroids and antihistamines -- improves asthma control and reduces asthma-related hospitalisation
• Allergen immunotherapy (subcutaneous or sublingual) targeting house dust mite can improve both rhinitis and asthma, and in children may reduce the risk of developing asthma

Reducing Triggers and Protecting Your Airways

Trigger avoidance, alongside medication, forms the foundation of asthma management. For house dust mite-driven asthma -- the most common pattern in Singapore:

• Use allergen-impermeable covers on all mattresses, pillows, and duvets
• Wash bedding weekly at 60 degrees Celsius (lower temperatures do not kill mites)
• Remove carpets from bedrooms and replace with hard flooring
• Maintain indoor humidity below 50% with air-conditioning -- dust mites cannot survive at low humidity
• HEPA vacuum cleaners and air purifiers reduce airborne allergen load

Additional measures for all asthma patients:

• Flu vaccination annually: Influenza is a common trigger of severe asthma attacks
• COVID-19 vaccination: COVID-19 infection can trigger severe asthma exacerbations
• Smoking cessation: Smoking significantly worsens asthma control and accelerates lung function decline
• Maintain a healthy weight: Obesity is independently associated with worse asthma control
• Monitor air quality (NEA PSI) and reduce outdoor activity during haze episodes

How Asthma is Diagnosed?

Asthma diagnosis requires both clinical assessment and objective measurement of airflow variability or bronchodilator reversibility. A symptom pattern alone is insufficient -- spirometry or equivalent lung function testing is essential for a reliable diagnosis.

• Spirometry: The primary lung function test for asthma. Measures FEV1 (forced expiratory volume in 1 second), FVC (forced vital capacity), and the FEV1/FVC ratio. Obstruction is defined as FEV1/FVC <0.70. Reversibility -- an increase in FEV1 of >200 ml and >12% after bronchodilator -- confirms variable airflow obstruction consistent with asthma.
• Bronchodilator Reversibility Test: Spirometry before and after administration of a short-acting bronchodilator (salbutamol 400 mcg). Significant reversibility confirms the variable, reversible airflow obstruction characteristic of asthma -- distinguishing it from COPD.
• Peak Expiratory Flow (PEF) Monitoring: A simple, inexpensive handheld device measures the speed of exhalation. Daily home PEF monitoring over 2 weeks showing variability >10% between morning and evening readings (diurnal variation) supports an asthma diagnosis and is also used for self-monitoring in asthma action plans.
• Exhaled Nitric Oxide: Measures nitric oxide in exhaled breath -- an indirect marker of eosinophilic airway inflammation. Elevated FeNO (>50 ppb) supports an asthma diagnosis and predicts response to inhaled corticosteroids. Used in phenotyping severe asthma and guiding biologic therapy selection.
• Bronchial Challenge Test: Inhalation of methacholine or mannitol to provoke airway narrowing. Used when symptoms suggest asthma but spirometry is normal -- confirms airway hyperresponsiveness. Particularly useful for diagnosing exercise-induced asthma or cough-variant asthma.
• Allergy Testing (Skin Prick or Specific IgE): Identifies the specific allergen triggers in allergic asthma. A positive result to house dust mite confirms the most common asthma trigger in Singapore. Results guide allergen avoidance measures and may indicate eligibility for allergen immunotherapy.
• Blood Eosinophil Count and Total IgE: Blood eosinophils are elevated in eosinophilic asthma and guide biologic therapy selection. Elevated total IgE supports allergic asthma. These tests are essential for assessment of severe uncontrolled asthma before biologic therapy.
• Chest X-ray: Normal in most asthma patients but used to exclude alternative diagnoses (infection, pneumothorax, foreign body). During severe attacks, may show hyperinflation or complications. Not diagnostic for asthma.
• Induced Sputum Eosinophil Count: Measures eosinophils in sputum collected after hypertonic saline inhalation. The gold standard for eosinophilic airway inflammation assessment. Used in specialist settings for phenotyping and guided corticosteroid dosing.