This study aims to assess the feasibility of capturing data on exhaled breath compounds during an acute asthma exacerbation. In addition to assessing the feasibility of such a study the investigators will collect data on exploratory outcomes including the ability of breath biomarkers to distinguish between controlled and exacerbated states and their ability to differentiate between triggers of exacerbation.

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.

Inclusion Criteria:

1. Male or female
2. Aged 18 or above
3. Able to provide informed consent
4. A confirmed asthma diagnosis requiring treatment with inhaled bronchodilator therapy +/- inhaled corticosteroids.
5. Non-smoker (or ex-smoker of 6 months or more with a less than 10 pack year history).
6. Current exacerbation or exacerbation within the previous 12 months.
7. Within 24 hours of having presented to acute secondary care (applicable to current exacerbation only)

Exclusion Criteria:

1. Major chronic cardiorespiratory disease other than asthma
2. Significant comorbid condition
3. Receiving maintenance oral corticosteroid therapy or other immunosuppressant or immunomodulatory therapy (including biologics)
4. Pregnant
5. Participating in a clinical trial of an investigational medicinal product (CTIMP).
6. Unable to speak English.

Adults aged 18+ with asthma diagnosis meeting British Thoracic Society guidelines.