The cause of asthma is not completely understood. However, genetics may be involved in many cases, as well as environmental influences and other factors.
Genetics
Various genes (e.g. those related to allergy) have been associated with an increased risk of developing asthma.
Environment
Environmental factors, such as exposure to allergens and pollutants, can trigger asthmas attacks. The airways can also develop sensitivity to a variety of different stimuli.
Other factors
Exercise, cold air and upper respiratory tract infections can also provoke attacks.