8 culprits for your chronic cough

You've been coughing for weeks. How do you know if it's just a hard-to-shake cold or something more serious? A chronic cough, defined as lasting more than eight weeks, is not uncommon.

Up to 40 percent of nonsmokers in the United States and Europe have reported a chronic cough at some point, and coughing is one of the five most common reasons for a doctor's visit.

Only a doctor can tell for sure what's behind your endless hacking.

However, in a 2006 study of women with an average age of 48 who had a cough lasting for six months, 39 percent were found to have asthma, 9 percent had chronic upper airway cough syndrome (commonly known as postnasal drip), and 9 percent had gastroesophageal reflux disease (GERD).

In addition, another 11 percent had chronic obstructive pulmonary disease (COPD), a serious, progressive disease that includes both emphysema and bronchitis. While not all people who develop COPD are smokers, people who smoke are at higher risk. Overall, 24 million Americans -- about 1 in 12 people -- have COPD, although half don't know they have the disease.

1. Asthma and allergies

Asthma is a chronic lung disease in which the airways in the lungs are prone to inflammation and swelling. Along with chest tightness, shortness of breath, and wheezing, coughing is a characteristic symptom of asthma, one which tends to intensify at night or in the early morning. When the symptoms of asthma flare up suddenly, it's known as an asthma attack.

Although it can begin at any age, asthma usually develops in childhood. Asthma triggers are different for everyone, and they can include exercise, colds, cigarette smoke and other airborne irritants, and certain foods. Asthmatics usually also have allergies.

Even in people without asthma, inhaling pollen, dust, pet dander, and other airborne irritants can trigger allergic rhinitis, an allergic reaction that can cause coughing, along with symptoms such as stuffy nose and sneezing.

You may be able to determine whether your cough is caused by allergies by keeping track of whether it comes and goes in certain situations. If your coughing magically stops when you step into an air-conditioned room on a dry, pollen-heavy day, or if gets worse every time you pet Mittens, you probably have allergies. If you're not sure what's triggering your allergic cough, your doctor can give you a skin test or blood test to pinpoint the allergy.

2. Chronic obstructive pulmonary disease

One condition that can cause a nagging cough is COPD, a lung condition that includes chronic bronchitis and emphysema.

COPD occurs when the airways and air sacs in the lungs become inflamed or damaged, most often due to smoking, and is more common after age 45. In COPD, the lungs produce excess mucus, which the body reflexively tries to clear by coughing. COPD-related tissue damage can also make it particularly difficult to expel air from the lungs, which can make you feel short of breath. Health.com: Young and short of breath: Could it be COPD?

Your doctor may check you for COPD (particularly if you have risk factors, such as smoking), after ruling out other common causes of cough. To determine if you have COPD, your doctor is likely to conduct some tests, including spirometry, which involves inhaling as deeply as you can and then exhaling into a tube.

3. Gastroesophageal reflux disease

GERD is an ailment of the stomach and esophagus that occurs when stomach acid backs up into the esophagus due to a weak valve. The main symptoms? Killer heartburn. But coughing is another common symptom of GERD, along with chest pain and wheezing. In fact, GERD is a fairly common, and unrecognize