(Health.com) -- You've been coughing for weeks. How do you know if it's just a hard-to-shake cold or something more serious?
Coughing is one of the five most common reasons for a doctor's visit.
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 unrecognized, cause of a chronic cough. Health.com: 7 surprising heartburn triggers
4. Respiratory tract infection
Coughing is one of the most common symptoms of colds and flu and other respiratory tract infections. The other symptoms that accompany colds and flu, such as stuffy nose and a fever, are telltale signs that a viral infection is causing your cough.
However, a cough can outlast all those other symptoms, perhaps because the air passages in your lungs remain sensitive and inflamed.When this occurs, it's called chronic upper airway cough syndrome (or postnasal drip).
A more serious respiratory tract infection is pneumonia, which can be caused by bacteria or viruses. A cough, often producing a greenish or rust-colored mucus, is one of the characteristic symptoms of the illness, along with fever, chills, chest pain, weakness, fatigue, and nausea. These symptoms may present differently depending on your age; older adults may not experience a fever, for instance, or they may have a cough but no mucus.
Pneumonia is treated with antibiotics and generally clears up within two or three weeks. As with the cold and flu, however, the cough can linger for much longer.
A form of pneumonia known as mycoplasma, or walking pneumonia, shares the symptoms of pneumonia (including cough) and is more common in people under the age of 40.
People who have COPD can be more susceptible to such respiratory tract infections, and may experience exacerbations episodes of potentially life-threatening shortness of breath when they catch a cold or breath in air pollution or other irritants. Health.com: I coughed so hard I passed out
5. Air pollution
Various pollutants and irritants in the air can cause a persistent cough. Even short-term exposure to fumes (such as diesel exhaust) can result in cough, phlegm, and lung irritation, for instance. Fumes can also exacerbate the symptoms of allergies or asthma.
Similarly, mold spores found in and around homes can cause wheezing and coughing when inhaled. In the wake of Hurricane Katrina, New Orleans reported a sudden spike in persistent cough complaints among returning residents. This so-called Katrina cough was believed to stem from the mold caused by the flooding, as well as by dry weather and the construction dust that was then ubiquitous in the city. Health.com: 5 ways to keep pollution from harming your heart
6. Acute bronchitis
If you're on the verge of recovering from a cold and suddenly develop a hacking, mucus-y cough, you probably have acute bronchitis, a condition in which the passageways in your lungs become infected and inflamed.
In addition to coughing and chest congestion, bronchitis can produce fever, chills, aches, sore throat, and other flu-like symptoms. These symptoms usually disappear within a few days, but the cough can persist for weeks.
If your cough doesn't go away, or if you develop acute bronchitis frequently, it may be a sign of a more serious condition. Acute bronchitis acute means short-term is different from chronic bronchitis. Chronic bronchitis is a condition in which the lungs produce excess mucus due to ongoing irritation, and is considered a form of COPD.
7. ACE inhibitors
ACE inhibitors are a type of medication used to treat high blood pressure and heart failure. About 42 million prescriptions for ACE inhibitors are written each year, and about 1 in 5 people who take the drugs develop a dry cough. In some people, the cough can persist for weeks after they stop taking the medication; women, African Americans, and Asians may be at greater risk of developing an ACE inhibitor cough than other people.
You should never stop taking a prescribed medication without consulting with your doctor, and ACE inhibitors are important medications for lowering blood pressure (a more serious condition than a cough.) Consult your doctor if you think your cough is related to a medication.
Also known as whooping cough, pertussis is a bacterial disease with symptoms that include a slight fever, a runny nose, and, most notably, a violent cough that can make breathing difficult.
Attempting to inhale air into the lungs between coughs can produce a distinctive, high-pitched whooping sound. After the initial stage, many people do not have a fever, but the chronic cough that accompanies pertussis can last for many weeks. Health.com: The germiest places in America
Most infants receive a pertussis vaccine, but its effectiveness subsides after about 10 years. Inadequate vaccination for pertussis (which is the "P" in the DPT shot) is one reason why the bacteria are making a comeback.
Once a very rare cause of chronic cough, the number of pertussis cases in the United States has risen alarmingly in recent years, especially among adolescents and adults. However, pertussis is still a relatively uncommon cause of chronic cough.
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