Asthma Breath Biomarker Assessment

This will be a longitudinal observational study in which the investigators assess the ability to capture information on volatile organic compounds in exhaled breath during an acute asthma exacerbation using two different approaches: A) Recruitment and assessment of patients in secondary care during an acute exacerbation of their asthma; patients to be re-assessed once their asthma is stable and controlled. B) Recruitment of clinically stable outpatients who are at increased risk of exacerbation by virtue of having had an acute exacerbation within the previous 12 months. Participants to be followed for a period of up to 12 months; assessed in the event of an exacerbation; and re-assessed once controlled.