The causes of asthma are not yet fully understood. Asthma development is influenced by both genetic and environmental factors but how these factors work together is still largely unknown.
Factors which influence the risk of asthma can be divided into those which cause the development of asthma and those which trigger asthma symptoms. The development factors are primarily genetic.
The factors that trigger asthma symptoms are environmental factors such as:
- Allergens from indoors or outdoors such as house dust mites, pets, pollen and moulds.
- Infections, usually viral.
- Occupational triggers
- Tobacco smoke
- Out/indoor air pollution
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Not everyone with asthma will have obvious allergies, some asthma patients display few or no identifiable triggers at all.