A cough that won’t go away usually has an identifiable, treatable cause. In adults, a cough lasting longer than eight weeks is classified as chronic, and the three most common reasons are postnasal drip, a form of asthma where coughing is the only symptom, and acid reflux. Less common but important causes include medication side effects, lingering infections, and workplace irritants.
Postnasal Drip
The single most common reason for a persistent cough is mucus draining down the back of your throat. Your nose and sinuses constantly produce mucus, but when production ramps up or the mucus thickens, the excess trickles down and irritates your throat, triggering a cough reflex. This is sometimes called upper airway cough syndrome.
The telltale signs go beyond the cough itself. You may feel a tickle in the back of your throat, have a frequent urge to clear your throat, or notice hoarseness and bad breath. The cough often gets worse at night when you’re lying down and gravity pulls more mucus toward your throat. Some people feel like there’s a lump in the back of their throat, and if enough mucus drains into your stomach, it can cause nausea.
Allergies, sinus infections, colds, and even dry air can all set off postnasal drip. If the cough started around the same time as nasal congestion or seasonal allergy symptoms, this is a likely culprit. Over-the-counter antihistamines and nasal saline rinses often help. When they don’t, sinus imaging can check for chronic sinus inflammation.
Cough-Variant Asthma
Most people picture wheezing and shortness of breath when they think of asthma, but there’s a form where a cough is your only symptom. Cough-variant asthma causes a chronic or recurring dry cough that comes in episodes lasting hours or days. Some people produce mucus, but most don’t. The cough may be triggered by cold air, exercise, dust, or strong scents.
This type of asthma is easy to miss because a standard physical exam can look completely normal. Diagnosis usually involves a breathing test called spirometry, which measures how well air moves through your lungs. If spirometry results are inconclusive, your doctor may have you inhale a substance that temporarily narrows the airways to see how reactive they are. Another common approach is a treatment trial: using an inhaler for two to four weeks to see if the cough improves. If it does, that essentially confirms the diagnosis.
Acid Reflux (Including Silent Reflux)
About 20% of people with a chronic cough have reflux as the underlying cause, and many of them never experience heartburn. This “silent” form of reflux, called laryngopharyngeal reflux, sends stomach acid high enough to irritate the throat and voice box directly. Even small amounts of acid reaching the airway can trigger persistent coughing.
Reflux triggers a cough through multiple pathways. Tiny amounts of stomach contents can be aspirated into the airway, directly irritating it. Acid in the lower esophagus can also stimulate the vagus nerve, which runs between your gut and your brain, setting off a cough reflex even without acid reaching your throat. Over time, repeated acid exposure makes the lining of your throat more sensitive, so even normal stimuli start triggering coughs.
Clues that reflux may be behind your cough include a sour taste in your mouth, a hoarse voice (especially in the morning), or a cough that worsens after meals or when lying down. If standard treatments for reflux don’t resolve the cough, a 24-hour test that monitors acid levels in your esophagus can confirm whether reflux is the problem.
Medication Side Effects
If you take a blood pressure medication in the ACE inhibitor class (common examples include lisinopril, enalapril, and ramipril), it may be causing your cough. Studies show that roughly 11% of people on these drugs develop a dry, persistent cough, though prescribing information historically underreported this number. The cough can start within weeks of beginning the medication or develop months later, which makes it easy to overlook the connection.
The fix is straightforward: switching to a different type of blood pressure medication typically resolves the cough within one to four weeks. If your cough started after beginning any new medication, it’s worth checking the side effect profile.
Lingering Infections
Some infections leave behind a cough that outlasts every other symptom. A common cold can produce a “post-infectious cough” that persists for weeks after you feel otherwise recovered, because the airways remain inflamed and hypersensitive.
Whooping cough (pertussis) deserves special mention. In adults, it often starts looking like an ordinary cold with a runny nose, mild fever, and occasional cough. Then, one to two weeks later, intense coughing fits develop. These fits typically last one to six weeks but can stretch to ten weeks. People who’ve had it describe it as the worst cough of their lives. Adults can get whooping cough even if they were vaccinated as children, since immunity fades over time. Recovery is slow, with the cough gradually becoming milder and less frequent.
Environmental and Workplace Triggers
A constant cough that improves on weekends or vacations points toward something in your environment. More than 400 workplace substances have been identified as possible triggers for airway irritation and occupational asthma. Wood dust affects carpenters and cabinetmakers. Flour and grain dust affect bakers and millers. Chemical fumes from paints, adhesives, and solvents affect workers across manufacturing. Even healthcare workers can develop coughs from latex exposure.
At home, mold, pet dander, dust mites, and strong cleaning products are common irritants. Smoking, including secondhand smoke, is an obvious cause that’s worth stating plainly: if you smoke and have a chronic cough, smoking is almost certainly the primary driver.
How the Cause Is Found
The diagnostic process typically starts with your history. When the cough started, whether it’s dry or productive, what makes it better or worse, what medications you take, and whether you smoke are all critical pieces. A chest X-ray is the standard first imaging step for most adults with an unexplained chronic cough, to rule out pneumonia, masses, or structural problems in the lungs.
If the chest X-ray looks normal, your doctor will likely work through the three most common causes in order: trying allergy or sinus treatments for postnasal drip, spirometry or an inhaler trial for asthma, and reflux treatment for GERD. This stepwise approach works because the big three causes account for the vast majority of chronic cough cases, and they sometimes overlap. It’s not unusual to have two contributing causes at once.
If the chest X-ray shows something abnormal, the next steps may include a CT scan, more detailed lung function testing, or a scope examination of the airways. CT is particularly important if there’s any concern about a mass or growth.
Signs That Need Prompt Attention
Most chronic coughs turn out to be caused by something manageable, but certain symptoms alongside a persistent cough warrant faster evaluation. Coughing up blood, even small streaks, is one. Unexplained weight loss, drenching night sweats, worsening shortness of breath, or chest pain are others. A new cough in a long-term smoker or former smoker, or a cough that changes character in someone who already has a chronic cough, also warrants a closer look sooner rather than later.