There are many potential sources of breathing problems, some minor and others more significant. Sometimes, simple anxiety can lead to difficulty breathing, such as during a panic attack. Other times, the cause is more serious, such as heart failure.

Any obstruction of the nose, mouth or throat can cause breathing problems. Injuries, diseases and toxins also can interfere with normal respiration.

Common causes of breathing problems include:

• Asthma. A condition where airways constrict, making breathing difficult.

• Emphysema.  An enlargement of the tiny air sacs of the lungs (alveoli) and deterioration of their  walls.
  
  
• Bronchitis. Inflammation of the airways (bronchial tubes). Breathing problems may occur in both acute bronchitis and chronic bronchitis.
  
  
• Chronic obstructive pulmonary disease (COPD). Continuous obstruction of the airways caused by emphysema or chronic bronchitis.
  
  
• Coronary artery disease. A disease in which blood flow is obstructed through the coronary arteries that supply the heart with oxygen-rich blood.
  
  
• Croup. A common respiratory illness that involves inflammation of the voice box (larynx) and windpipe (trachea). The condition primarily affects infants and young children.
  
  
• Deconditioning. The medical term for lack of exercise that contributes to poor lung function. Lack of exercise is also often associated with obesity, which is a condition that can further deteriorate lung function.
  
  
• Heart arrhythmia. An abnormal heartbeat that may be unusually fast or unusually slow.
  
  
• Heart attack (myocardial infarction). A condition where blood supply is partially cut off from the heart, leading to the death of heart muscle (myocardium) from lack of oxygen.
  
  
• Heart failure. A condition in which the heart is unable to pump enough blood to meet the body's demands. This leads to congestion within the blood vessels and may cause fluid backup and swelling (edema) in the lungs, legs and ankles.
  
  
• Interstitial lung disease. A category of chronic lung disorders characterized by scarring and inflammation.
  
  
• Medication side effects. Unintended side effect of some heart medications, such as beta blockers.
  
  
• Pneumothorax (or “collapsed lung”). A pocket of air between the two layers of the pleura, the thin membrane that covers the interior chest wall and the lungs.
  
  
• Pulmonary embolism. A sudden blocking of an artery of the lung, usually due to a blood clot.
  
  
• Pulmonary edema. A build-up of fluid in the lungs that results when the heart does not pump adequately.
  
  
• Pulmonary hypertension. Characterized by high blood pressure (hypertension) in the blood vessels that supply oxygen-poor blood to the lungs.
  
  
• Sleep apnea. A group of disorders in which a person periodically stops breathing during sleep, decreasing oxygen and increasing carbon dioxide in the blood.
  
  
• Whooping cough. A contagious disease in which a dry cough worsens over time, producing a “whooping” sound. Other symptoms include fever, runny nose, sneezing and possible vomiting. A vaccine is available.

Other potential triggers for breathing problems include:

• Allergic reaction
  
  
• Other forms of heart disease
  
  
• Digestive conditions (such as gastroesophageal reflux disease)
  
  
• Injuries to the chest, neck or lungs
  
  
• Tobacco smoke
  
  
• Dust and other workplace irritants (e.g., chemicals, solvents, paints)
  
  
• Pneumonia
  
  
• Drug overdose
  
  
• High altitude
  
  
• Obesity
  
  
• Airway obstruction or choking
  
  
• Seizures
  
  
• Metabolic disorders (such as anemia)
  
  
• Compression of the chest wall

Air pollution is often responsible for worsening respiratory conditions and causing breathing problems, particularly in metropolitan areas. In particular, air pollution has been linked to an increased risk of asthma and allergies, particularly in unborn children.