No one really knows exactly what causes asthma. In asthma, the irritation of your ultrasensitive airways results to the three changes:

• cells in your air passages produce excessively thick and sticky mucus that tends to clog your airways
• your air passages swell or become inflamed
• the muscles in your airways constrict and tighten

These changes cause your air passages to narrow or cnstrict, causing difficulty in breathing, wheezing, and tightness in the chest.