Breathing difficulties can be described in several different ways. If you are having trouble breathing, you may feel "winded," short of breath, unable to take a deep breath, "air hunger" (you are not getting enough air), or like you are gasping for air.

See first aid for choking.

If you are having difficulty breathing, it is almost always a medical emergency (other than feeling slightly winded from normal activity like exercise or climbing a hill).

Difficulty breathing has many potential causes. Some of the most common are:

• Sudden illness or infections like pneumonia, acute bronchitis, whooping cough, croup, or epiglottitis (inflammation of the epiglottis -- the flap that closes the windpipe when you swallow)
• Ongoing medical problems like heart disease, asthma, emphysema, chronic bronchitis, or heart failure (which causes shortness of breath because fluid backs up into the lungs)
• Heart attack
• Injury to the neck, chest wall, or lungs
• Collapsed lung, which can happen if you have emphysema or asthma, but may also happen spontaneously in young, healthy people
• High altitudes, which can be a problem even in young people
• Cigarette smoking or breathing secondhand smoke
• Pulmonary embolism, or a blood clot in the lung, which can cause very abrupt and severe difficulty breathing
• Life-threatening allergic reaction