Asthma is a condition that affects the airways — the small tubes that carry air in and out of the lungs.
When a person with asthma comes into contact with an asthma trigger, the muscles around the walls of the airways tighten and the airways become narrower.
The lining of the airways becomes red and swollen and often sticky mucus or phlegm is produced.
All these reactions cause the airways to become narrower and irritated — leading to the symptoms of asthma.
These videos about asthma and living with it were made by Asthma UK.
For more information on asthma, visit asthma.org.uk