Suspected causes of asthma include:
[ul]genetic predisposition
allergic response
vitamin deficiency (vitamins A and B)
psychosomatic
incorrect breathing technique
mineral deficiency
other dietary deficiencies[/ul]
Asthma is complex and causes could be different in different people or more than one cause.
Source: Tai Chi for Better Breathing: relaxation exercises for asthma relief and overall good health; by Gary Khor (2001). Pages 14-15.