Asthma is a chronic disease involving the airways in the lungs, which allow the air to come in and out of the lungs. Asthma is characterised by inflammation, oedema (lining of the airways are swollen) and bronchospasm (narrowing of the tubes which carry the air). These especially occur as a result of the stimuli (allergic asthma), like dust, pet dander, pollen or mold. As a result of abnormal immune reaction, these factors cause the passages in the airways of the lungs to become inflamed and swollen. This results in coughing and wheezing, as the most common asthma symptoms.