Asthma is a common disease usually with onset in childhood. It is characterized by airway hyperreactivity with acute episodic narrowing, particularly following environmental triggers. This disease affects approximately 3% to 8% of the population, and despite medical management, results in 2,000 to 3,000 deaths annually in the United States. Based on autopsy findings, an acute attack results in alternating areas of atelectasis and hyperexpansion of the lungs. Microscopic features of asthma include marked thickening of airway smooth muscle, submucosal edema and vascular dilation, thickening of the basal lamina of the mucosa, increased numbers of mucosal goblet cells, and mucus plugs within small to medium bronchi. The airway walls typically show a mixed inflammatory infiltrate that includes numerous eosinophils, as well as plasma cells, lymphocytes, and neutrophils. Adjacent alveolar infiltrates may be present. The mucous plugs and sputum from asthmatic patients may contain admixed inflammatory cells, particularly eosinophils, and may also show Curschmann spirals, Charcot-Leyden crystals (formed from degranulated eosinophils), or Creola bodies (sloughed respiratory epithelium).