Shortness of breath is the feeling of difficult or uncomfortable breathing. Most people experience shortness of breath if they exercise harder or do some heavier work then they have before. In a healthy person, shortness of breath improves with rest. There are many physical disorders that may cause shortness of breath.

Shortness of breath happens when the body's needs exceed the ability of the lungs and chest muscles to deliver oxygen. If it occurs often over a long period, it can put a strain on the heart and lungs. There are many possible causes. Various lung disorders that cause shortness of breath include:
* lung damage from smoking or exposure to dusts or chemicals,
* asthma, emphysema, and other airways obstruction,
* restrictive diseases, such as fibrosis,
* cancer,
* pneumonia and other infections, or
* a collapsed lung.

Shortness of breath can also be caused by heart disease or heart failure. Some heart problems cause breathing distress only when one is lying down or sleeping. It usually stops when the person sits up or stands, but is a sign of a serious problem. Other causes include:
* chronic anemia,
* hemorrhage,
* diabetes,
* a brain lesion,
* choking, for example on food,
* swollen tonsils,
* a bee sting in the mouth or throat, and
* rapid breathing due to feeling anxious.

If you have a hard time breathing or a marked change in exercise tolerance, consult your healthcare provider. If you are a smoker, stop now.

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