What is Asthma? Asthma is a common lung disorder in which the inner lining of the small breathing tubes of the lungs, the bronchioles, become inflamed and swollen. At times this leads to spasms or narrowing of these tubes. This can cause wheezing,shortness of breath, and/or tightness in the chest. Cough, especially with exercise or in the middle of the night, is particularly common in asthma. In mild asthma, the only symptom may be cough. Wheezing may not occur, or may only be heard by your doctor listening with a stethoscope.