Visualization of the symptoms of bronchial hyperreactivity, which is caused by asthma. Bronchial hyperreactivity develops when the smooth muscle that surrounds the bronchiole contracts and constricts the walls of the bronchiole. This muscle constriction will cause irritation, swelling, smaller airways, and excessive mucus production. When the bronchiole pathways get smaller and fill with mucus, there is little room left for air. Breathing then becomes difficult and may be accompanied by wheezing or coughing.