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Asthma is a disease of the lungs. People with asthma experience episodes of asthma, or asthma attacks. This occurs when there is a narrowing and inflammation of the airways, which makes it harder to breathe.
The lungs provide an interface between the air that we breathe in and the bloodstream. When a person breathes, air is drawn in through the nose and mouth and down through the trachea. The trachea divides into two bronchi, a right main bronchus and left main bronchus, to supply each lung.
The bronchi divide into smaller bronchi, and then into bronchioles which ultimately terminate in the alveoli – the folded membranes where gas exchange takes place. The bronchi and bronchioles have a muscular layer in the wall which allows them to contract. In an acute asthma attack, this muscular layer contracts and leads to narrowing of the airways.
Inflammation may still be present between asthma attacks. This makes the airways sensitive and more likely to react to asthma triggers and cause an acute asthma attack.
Asthma is sometimes divided into four main groups as follows:
- Atopic asthma: This is the most common and classic type of asthma. Patients normally have relatives who have atopic asthma, and themselves experience other allergic diseases (e.g. food allergy, eczema, hayfever). House dust mites (HDM), pollen and animal fur are common triggers.
- Non-atopic asthma: This type is triggered by respiratory infections in patients without a family history or other allergic traits.
- Drug-induced asthma: Aspirin medication can sometimes induce asthma attacks and urticaria in susceptible individuals.
- Occupational asthma: This form of asthma is induced by small quantities of chemicals and fumes, usually following repeated exposure.