Asthma is a heterogeneous disease, usually characterised by chronic airway inflammation. It is defined by a history of respiratory symptoms such as wheeze, shortness of breath, chest tightness and cough that vary over time and in intensity, together with variable expiratory airflow limitation.

The underlying pathological processes of asthma vary between individuals. Each person’s asthma has different characteristics, pattern of triggers and their response to treatment may also vary. This variability is sometimes referred to as phenotypes. Phenotypes are normally grouped using clinical characteristics such as symptoms, inflammation and pulmonary function. Some of the most common phenotypes include:

1. Allergic asthma: most easily recognisable, it starts in childhood and is associated with past and/or family history of allergic disease. Induced sputum examination often reveals eosinophilic inflammation and patients usually respond well to inhaled corticosteroids (ICS)
2. Non-allergic asthma: adult asthma that is not associated with allergy. The cellular profile of the sputum may be neutrophilic, eosinophilic, or contain few inflammatory cells. These patients respond less well to ICS
3. Late-onset asthma: initial onset of asthma in adulthood (particularly in women). It tends to be non-allergic, often requires higher doses of ICS or is relatively refractory to ICS
4. Asthma with fixed airflow limitation: patients with longstanding asthma who develop fixed airflow limitation, thought to be due to airway wall remodelling 
5. Asthma with obesity: patients in the obese category of body mass index (BMI) with asthma who have prominent respiratory symptoms and little eosinophilic airway inflammation. 

These different phenotypes can influence treatment choice, such as when to add in a leukotriene-receptor antagonist (LTRA) and response to ICS. Taking an individual approach for each person with asthma means their personalised asthma action plan (PAAP) can take into consideration the most appropriate management for the individual’s symptoms and response to treatment.