Asthma is a disease causing difficulty in breathing, with recognizable symptoms: episodic wheezy breathlessness, which varies considerably within short periods of time, and is reversible (but not completely so in some patients) either spontaneously or with treatment.

Characteristics of Asthma Episodes of wheezy difficulty in breathing Narrowing of the air passages in the lungs and hence increased resistance to airflow. The narrowing is due to different combinations of: contraction of muscles around the air passages swelling of the airway lining due to airway inflammation excessive mucus in the airways Rapid and considerable changes in airway obstruction (peak flow variation >= 20%) Frequent nocturnal episodes and low morning peak flow values Significant reversibility with drugs which resemble adrenaline, the beta2 agonists Significant reversibility with steroid drugs Symptom-free periods Frequent occurrence of allergy Inflammation of the air passages, characterized by eosinophils in the airway wall Bronchial hyper-responsiveness to nonspecific stimuli such as cold air or histamine