What is wheezing? Wheezing is a whistling sound made during inhalation or exhalation. Wheezing can result from either of two respiratory conditions: reduced airflow resulting from narrowing of the airways or congestion in the lungs. Causes of wheezing include asthma and infection and inflammation of the lungs (pneumonia) or bronchi (bronchitis). Other common causes include chronic obstructive pulmonary disease (COPD), bronchiectasis (destruction and widening of the airways), cystic fibrosis, and tuberculosis. Lung cancer can cause wheezing that is accompanied by a cough that may bring up bloody sputum (hemoptysis). Heart conditions can also lead to wheezing, such as when an acute episode of congestive heart failure leads to fluid buildup in the lungs. Another less common cause of wheezing is a serious allergic reaction (anaphylaxis), which may be accompanied by severe shortness of breath, chest pain, and sudden swelling of the throat, face and lips. In some cases, wheezing can be a sign of a serious or life-threatening condition. Seek immediate medical care (call 911) if you, or someone you are with, have serious symptoms, such as severe difficulty breathing and sharp chest pain, which may be accompanied by pale or blue lips, a change in level of consciousness or alertness, or rapid heart rate. Seek immediate medical care for sudden swelling of the throat, face, or lips, and difficulty breathing, as these can be signs of an anaphylactic reaction. Seek prompt medical care if you are being treated for wheezing but mild symptoms recur or are persistent.