Asthma is a chronic disease that causes the airways of the lungs to swell and narrow reducing the amount of air that can pass through the air way. It leads to breathing difficulty such as wheezing, shortness of breath, chest tightness, and coughing. Asthma symptoms can becaused by breathing in substances called allergens or triggers, or by other causes. Common trigger include animal hair, dust, mites, mold, pollen, respiratory infection, etc. Wheezing or a cough maybe the main symptom.