Wheezing is caused by air passing through narrowed air passageways in the lung. Narrowing of the air passageways, called bronchioles, may be caused by spasm of the muscles in the wall of the bronchioles, or caused by mucus that lines the inside wall of the bronchioles.

The most common causes of wheezing include:

• Asthma
• Chronic obstructive lung disease

Additional causes of wheezing include:

• Allergic reactions
• Airway foreign body
• Beta-blocker medications
• Bronchitis
• Colds
• Cystic fibrosis
• Heart failure
• Influenza
• Lung cancer
• Pneumonia
• Pulmonary embolism
• Tuberculosis