A cough that won’t go away usually comes down to one of three causes: mucus draining down the back of your throat, asthma, or acid reflux from the stomach. Together, these account for up to 90 percent of all chronic cough cases in adults. If your cough has lasted longer than three weeks but less than eight, it’s classified as subacute. Beyond eight weeks, it’s considered chronic.
The good news is that a persistent cough is rarely a sign of something dangerous. But figuring out the specific cause matters, because each one responds to different treatment. Here’s what could be going on.
Postnasal Drip: The Most Overlooked Cause
When your nose and sinuses produce excess mucus, it drains down the back of your throat and irritates the tissue there. This triggers a cough reflex that can last for weeks or months, especially if the underlying issue (allergies, a lingering sinus infection, cold air) isn’t addressed. You might not even realize it’s happening.
The telltale signs go beyond the cough itself. You may feel a tickle in the back of your throat, have the constant urge to clear your throat, or notice a sore throat that comes and goes. Some people feel a lump-like sensation in the throat. Bad breath, hoarseness, and frequent swallowing are also common. The cough often gets worse at night when you’re lying down and gravity lets mucus pool in your throat. In some cases, enough mucus drains into your stomach to cause nausea.
Cough-Variant Asthma
Most people picture asthma as wheezing and shortness of breath, but there’s a form where cough is the only symptom. No chest tightness, no audible wheeze. Just a dry, persistent cough that tends to flare up with exercise, cold air, allergens, or respiratory infections.
This type of asthma is tricky to identify because standard breathing tests can come back normal between flare-ups. Your doctor may use a bronchoprovocation test, where you inhale a substance that temporarily narrows the airways to see how reactive they are. Another common approach is a trial of asthma medication. If the cough goes away with treatment, that’s often enough to confirm the diagnosis.
Acid Reflux You Might Not Feel
Acid reflux doesn’t always come with heartburn. In many people with a reflux-related cough, the classic burning sensation is mild or completely absent. This is sometimes called “silent reflux,” and it catches people off guard because they don’t connect their cough to their stomach.
The mechanism works two ways. Acid rising from the stomach can directly irritate cough receptors in the throat and upper airway. It can also trigger a nerve reflex (through the vagus nerve, which connects the esophagus to the lungs) that causes your lower airways to produce more mucus and become more sensitive. Over time, repeated reflux thickens the lining of the lower esophagus and can make both problems worse. Clues that reflux is driving your cough include the cough worsening after meals, when lying flat, or alongside a sour taste in your mouth.
A Cough Left Over From a Cold or Infection
If your cough started during a cold, flu, or COVID infection and just never fully went away, you’re dealing with a post-infectious cough. This is the most common cause of coughs in the three-to-eight-week range. The original infection is gone, but it left behind irritated, hypersensitive airways. Your cough reflex nerves are essentially stuck on high alert, firing at stimuli that wouldn’t normally bother you: a change in air temperature, talking for a long time, or a deep breath.
Post-infectious coughs generally resolve on their own, though they can take up to eight weeks. If yours pushes past that mark, it’s worth investigating other causes that may have been unmasked or worsened by the infection.
Blood Pressure Medication
A class of blood pressure drugs called ACE inhibitors causes a dry, persistent cough in roughly 5 to 39 percent of people who take them, with one large study finding an overall prevalence of 19 percent. If your cough started within weeks or months of beginning a new blood pressure medication, this could be the connection. Common ACE inhibitors have names ending in “-pril” (lisinopril, enalapril, ramipril). The cough typically resolves after switching to a different type of medication, though it can take a few weeks to fully clear.
Environmental and Workplace Triggers
Chemicals, dust, and airborne particles you encounter regularly can sustain a chronic cough even if you don’t think of your environment as “toxic.” Ammonia, cleaning products, construction dust, smoke (including secondhand tobacco and marijuana smoke), and industrial fumes all qualify. These irritants can stimulate cough receptors directly or trigger secondary problems like bronchitis, sinus inflammation, or cough-variant asthma.
The key question is timing. Does your cough improve on weekends, vacations, or when you’re away from a specific environment? If so, the exposure itself may be the primary driver, and reducing or eliminating it is the most effective treatment.
How Doctors Figure Out the Cause
Because the top three causes of chronic cough can overlap (some people have two or even all three at once), diagnosis often involves a process of elimination. A chest X-ray is usually the first step, not because it’s great at detecting the most common causes, but because it can rule out less common but serious ones like pneumonia or lung cancer. Sinus X-rays or a CT scan can reveal hidden sinus infections contributing to postnasal drip.
Spirometry, a simple breathing test where you blow into a device as hard and fast as you can, measures how well air moves through your lungs and helps identify asthma or chronic obstructive lung disease. If your results are normal but asthma is still suspected, a bronchoprovocation test may follow. In some cases, a doctor will use a thin flexible scope (rhinoscopy) to look directly at your nasal passages, sinuses, and upper airway for signs of inflammation, polyps, or structural issues.
Often, though, the diagnostic approach is more practical than high-tech. Your doctor may simply treat the most likely cause first and see if the cough improves. If treating postnasal drip doesn’t help, they move on to asthma therapy, then reflux management. This stepwise approach works because treatment response is itself diagnostic.
Signs That Need Prompt Attention
Most persistent coughs are annoying but not dangerous. However, certain symptoms alongside a cough signal something more serious. Coughing up blood, even small amounts, warrants a prompt medical visit. So does unexplained weight loss, a cough that disturbs your sleep night after night, or one that’s severe enough to interfere with work or school. A new cough in a long-term smoker or a change in the character of an existing smoker’s cough also deserves evaluation, as these can be early signs of lung disease.