Asthma — Causes, Symptoms, Triggers & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Asthma is a chronic inflammatory disease of the airways characterised by variable and recurring episodes of airflow obstruction, bronchial hyperresponsiveness, and airway remodelling. It affects approximately 262 million people worldwide, making it one of the most prevalent non-communicable diseases globally. The underlying pathology involves persistent airway inflammation driven by Th2 lymphocytes, mast cells, and eosinophils, leading to airway wall thickening, increased mucus secretion, and smooth muscle hypertrophy. Asthma is classified by severity (intermittent, mild persistent, moderate persistent, severe persistent) and by phenotype — allergic (atopic), non-allergic, late-onset, and severe eosinophilic — each with distinct treatment implications. The majority of asthma deaths (approximately 1,000 per day globally) are preventable with appropriate management. Asthma is not a single disease but a syndrome with multiple phenotypes driven by distinct biological pathways, which explains why treatment response varies significantly between patients and underscores the growing need for personalised medicine approaches in difficult-to-treat and severe cases.

Asthma results from a complex interaction between genetic susceptibility and environmental exposures. Host factors: atopy (personal or family history of eczema, allergic rhinitis, or food allergy — the strongest predisposing factor); female sex after puberty; obesity (BMI above 30 doubles asthma risk); ORMDL3 and ADAM33 gene variants; and prematurity or low birthweight. Environmental triggers and sensitising agents: house dust mite allergens (the most common trigger globally), pet dander (cat, dog), cockroach allergens, outdoor pollens and moulds, tobacco smoke (both active and passive — critical in children), air pollution (particulate matter PM2.5, ozone), occupational sensitisers (isocyanates in spray painters; flour dust in bakers — occupational asthma accounts for 15% of adult-onset asthma), aspirin and NSAIDs (aspirin-exacerbated respiratory disease, AERD), beta-blockers, cold air, exercise, respiratory viral infections (rhinovirus being the most frequent exacerbation trigger), and emotional stress.

The cardinal symptoms are wheeze (high-pitched musical sound from turbulent airflow in narrowed airways), breathlessness (dyspnoea — typically disproportionate to exertion), chest tightness (described as a band or pressure across the chest), and cough (often dry, irritating — nocturnal cough waking the patient is a particularly suggestive symptom). These symptoms characteristically vary over time and in intensity, are typically worse at night or early morning, and are provoked by specific triggers including exercise, allergens, cold air, and respiratory infections. Signs of an acute severe asthma attack: inability to complete sentences in one breath, respiratory rate above 25/min, peak expiratory flow (PEF) below 50% predicted, oxygen saturation below 92%, tachycardia above 110/min, use of accessory respiratory muscles, and silent chest on auscultation (a sign of life-threatening asthma — impending respiratory arrest).

Diagnosis is based on characteristic symptoms plus objective demonstration of variable airflow limitation. Spirometry is the standard test: pre- and post-bronchodilator FEV1 and FVC measurement; a significant bronchodilator response (FEV1 increase of at least 12% and 200 mL after 400 mcg salbutamol) confirms reversible airflow obstruction. Peak expiratory flow (PEF) variability greater than 10% on serial measurements over 2 weeks supports the diagnosis. Bronchial challenge testing with methacholine or mannitol (for patients with normal spirometry): a PC20 below 8 mg/mL methacholine indicates bronchial hyperresponsiveness. Fractional exhaled nitric oxide (FeNO) above 40 ppb identifies eosinophilic airway inflammation, supporting ICS responsiveness. Full blood count with eosinophil count, serum total and specific IgE, and skin prick testing characterise the allergic phenotype. Chest X-ray (hyperinflation in acute attack; excludes pneumothorax, infection) and CT chest for complex cases.

GINA (Global Initiative for Asthma) 2024 guidelines recommend a stepwise approach. Step 1 (intermittent symptoms): low-dose ICS-formoterol (budesonide-formoterol) used as-needed — preferred over SABA alone as it reduces exacerbation risk. Step 2 (mild persistent): regular low-dose ICS (beclomethasone 200 mcg/day, budesonide 200 mcg/day, or fluticasone propionate 100 mcg/day) plus as-needed SABA. Step 3 (moderate persistent): low-dose ICS-LABA combination (budesonide-formoterol, fluticasone-salmeterol). Step 4 (severe persistent): medium-dose ICS-LABA; add-on tiotropium (LAMA); consider specialist referral. Step 5 (severe refractory asthma): biologic therapy — anti-IgE (omalizumab, for allergic asthma with elevated IgE); anti-IL-5 (mepolizumab, benralizumab — for eosinophilic asthma with blood eosinophils above 300 cells/microL); anti-IL-4/IL-13 (dupilumab — for type 2 asthma); anti-TSLP (tezepelumab — broadest indication, effective regardless of eosinophil count). Acute severe asthma: high-flow oxygen (target SpO2 94-98%), nebulised salbutamol plus ipratropium, IV hydrocortisone 100 mg or oral prednisolone 40-50 mg for 5 days, and magnesium sulphate 2 g IV for life-threatening attacks.

Uncontrolled asthma leads to serious and potentially irreversible complications. Airway remodelling occurs when chronic uncontrolled eosinophilic inflammation produces structural changes — subepithelial fibrosis, smooth muscle hypertrophy, and goblet cell hyperplasia — resulting in fixed (irreversible) airflow obstruction resembling COPD. Approximately 20% of asthma patients develop fixed airflow limitation over 10-20 years of uncontrolled disease. Acute severe asthma attacks (status asthmaticus) that are inadequately managed can cause acute respiratory failure requiring mechanical ventilation, with a mortality of 1-2 per 100 hospitalisations. Life-threatening asthma causes approximately 1,000 preventable deaths annually in the UK alone, the majority in patients with suboptimal preventer therapy. Pneumothorax and pneumomediastinum can complicate severe exacerbations. Oral corticosteroid dependence in severe asthma causes systemic steroid toxicity: osteoporosis, adrenal suppression, diabetes, hypertension, and cataracts. Exercise-induced bronchospasm limits physical activity, contributing to obesity, cardiovascular risk, and poor mental health. Sleep-disordered breathing from nocturnal asthma significantly impairs daytime function.

Identify and avoid personal triggers through an asthma action plan — a written plan specifying medications to take when symptoms worsen, when to seek emergency care, and how to adjust treatment based on peak flow readings. Allergen avoidance: use impermeable mattress and pillow covers for house dust mite sensitisation; remove pets from sleeping areas; avoid tobacco smoke completely. Smoking cessation is the single most impactful intervention for adult-onset asthma — smoking reduces ICS efficacy and accelerates lung function decline. Flu vaccination annually and COVID-19 vaccination reduce exacerbation risk. Exercise-induced asthma is managed with pre-exercise SABA or ICS-formoterol and is not a contraindication to exercise — regular physical activity improves asthma control. Maintain healthy weight — weight loss of 5-10% significantly improves asthma control in obese patients. Ensure correct inhaler technique at every clinic visit — incorrect technique occurs in up to 80% of patients and renders treatment ineffective.

See a doctor urgently or attend an emergency department if: you are unable to speak in full sentences due to breathlessness; your reliever inhaler is not improving symptoms after 10-15 minutes; your peak flow reading is below 50% of your personal best; you develop severe chest tightness or cyanosis (blue lips); or you feel your asthma attack is the worst you have ever experienced. After any acute asthma episode requiring emergency care, a follow-up appointment within one week is recommended to review your preventer treatment and asthma action plan. Seek a GP review if you are using your reliever inhaler more than twice a week, waking at night with asthma symptoms, or if your symptoms are limiting daily activities — this indicates uncontrolled asthma requiring treatment escalation.