Causes, incidence, and risk factors
Asthma is caused by inflammation in the airways. When an asthma attack occurs, the muscles surrounding the airways become tight and the lining of the air passages swells. This reduces the amount of air that can pass by.
In sensitive people, asthma symptoms can be triggered by breathing in allergy-causing substances (called allergens or triggers).
Common asthma triggers include:
Animals (pet hair or dander)
Changes in weather (most often cold weather)
Chemicals in the air or in food
Respiratory infections, such as the common cold
Strong emotions (stress)
Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) provoke asthma in some patients.
Many people with asthma have a personal or family history of allergies, such as hay fever (allergic rhinitis) or eczema. Others have no history of allergies.
Most people with asthma have attacks separated by symptom-free periods. Some people have long-term shortness of breath with episodes of increased shortness of breath. Either wheezing or a cough may be the main symptom.
Asthma attacks can last for minutes to days, and can become dangerous if the airflow is severely restricted.