A cough that won’t go away usually falls into one of a handful of common categories, and the cause often isn’t what you’d expect. Doctors classify coughs by duration: acute (under 3 weeks), subacute (3 to 8 weeks), and chronic (longer than 8 weeks). If yours has lingered past the 3-week mark, it’s no longer a typical cold, and identifying the underlying trigger is the key to making it stop.
The three most common causes of a persistent cough in adults are post-nasal drip, acid reflux, and a form of asthma where coughing is the only symptom. Together, these account for the vast majority of cases. But medications, lingering infections, air quality, and nerve sensitivity can all play a role too.
Post-Nasal Drip
The most frequent culprit behind a nagging cough is mucus draining from your sinuses down the back of your throat, a condition now called upper airway cough syndrome. That dripping mucus irritates nerve endings in your throat and voice box, triggering the cough reflex. Allergies, sinus infections, and even cold, dry air can keep this cycle going for weeks or months.
What makes this tricky is that about 20% of people with post-nasal drip don’t even realize they have it. You might not feel the drip itself, yet the constant low-level irritation keeps your throat in a reactive state. Over time, the lining of your throat can become inflamed and swollen, which may make the cough reflex even more sensitive. Common clues include frequent throat clearing, a feeling of something stuck in your throat, or a cough that’s worse when you lie down at night.
Acid Reflux Without Heartburn
Acid reflux causes roughly 25% of persistent coughs in adults, and up to 40% when more sensitive testing is used. The surprising part: up to 75% of people whose cough is driven by reflux have no heartburn or other obvious stomach symptoms. This is sometimes called “silent reflux.”
Two things happen when stomach contents travel upward. First, acid in the esophagus can activate a nerve reflex that signals the airways to cough, even though nothing has reached your lungs. Second, tiny amounts of stomach fluid can creep high enough to irritate the voice box or get inhaled into the lower airways (microaspiration). Both pathways trigger coughing. If your cough is worse after meals, when bending over, or when lying flat, reflux is worth investigating even if you’ve never had classic heartburn symptoms.
Cough-Variant Asthma
Not all asthma involves wheezing or shortness of breath. In cough-variant asthma, a dry, persistent cough is the only symptom. The airways are inflamed and overly reactive, but standard breathing may feel completely normal between coughing episodes. This makes it easy to overlook.
Diagnosis typically involves lung function testing (spirometry) and sometimes a trial of asthma medications. If your cough improves with an inhaler, that response itself helps confirm the diagnosis. Cough-variant asthma can be triggered by exercise, cold air, allergens, or respiratory infections, and it sometimes progresses to typical asthma if left untreated.
A Lingering Cough After a Cold or Infection
If your cough started during a cold, flu, or COVID infection and simply never went away, you likely have a post-infectious cough. The original virus is gone, but it left behind inflamed, hypersensitive airways. This type of cough typically resolves within several weeks but can persist in the subacute window of 3 to 8 weeks, sometimes longer.
Post-infectious coughs are usually dry or produce only small amounts of clear mucus. They tend to improve gradually on their own. If yours hasn’t budged after 8 weeks, it’s worth looking deeper for one of the other causes on this list, since the infection may have simply unmasked an underlying issue like reflux or asthma.
Blood Pressure Medications
ACE inhibitors, a widely prescribed class of blood pressure drugs, cause a persistent dry cough in anywhere from 4% to 35% of people who take them. The cough is typically dry with a tickling or scratching sensation in the throat. It can start within days of beginning the medication or develop months later, which makes the connection easy to miss.
About one in five patients on these medications ends up stopping them because of this side effect. If your persistent cough started sometime after beginning a blood pressure medication, check whether it’s an ACE inhibitor (common names end in “-pril,” like lisinopril or enalapril). Switching to a different class of blood pressure drug usually resolves the cough within a few weeks.
Nerve Sensitivity and Unexplained Cough
Around 40% of adults referred to a specialist for chronic cough either have no identifiable cause or keep coughing despite treatment for the conditions listed above. Researchers now understand that many of these cases involve cough hypersensitivity, where the nerves controlling the cough reflex become abnormally reactive.
The vagus nerve, which runs from your brainstem down through your throat, chest, and gut, plays a central role. In people with cough hypersensitivity, ordinary stimuli that wouldn’t bother most people (temperature changes, talking, laughing, certain smells, even touching the ear canal) can trigger intense coughing. This heightened sensitivity in the voice box and airways is increasingly recognized as a condition in its own right, not just a mystery diagnosis. For these refractory cases, nerve-calming medications originally designed for pain or seizures have shown benefit. One meta-analysis found these drugs were 37% more effective than placebo at reducing cough.
Air Quality and Environmental Irritants
Long-term exposure to air pollution is a genuine risk factor for persistent cough. A large meta-analysis found that for every modest increase in fine particulate matter (the tiny particles from traffic exhaust, wildfires, and industrial emissions), the odds of chronic cough rose by 9% to 38%. Nitrogen dioxide, another common urban pollutant, showed a statistically significant 4% increase in cough risk per unit of exposure.
Beyond outdoor pollution, indoor irritants matter too. Cigarette smoke (including secondhand), mold, strong cleaning products, and dust are all common triggers. If your cough improves noticeably when you travel or spend time away from your usual environment, that’s a meaningful clue.
Eosinophilic Bronchitis
This under-recognized condition causes a chronic cough that looks a lot like asthma on the surface, but lung function tests come back completely normal. The difference is that the inflammation involves a specific type of immune cell (eosinophils) building up in the airways without causing the airway narrowing that defines asthma. Chest X-rays are normal too, which can lead to frustration when test after test shows nothing wrong.
Diagnosis requires a sputum test showing elevated eosinophil levels (3% or higher). The good news is that it responds well to inhaled corticosteroids, the same type of medication used for asthma. If you’ve been told your lungs look fine but you’re still coughing, this is worth asking about.
Symptoms That Need Prompt Attention
Most persistent coughs are caused by the benign conditions above, but certain accompanying symptoms signal something more serious. Coughing up blood, unexplained weight loss, drenching night sweats, progressive shortness of breath, persistent hoarseness, difficulty swallowing, or a new cough in a long-term smoker all warrant prompt evaluation, typically with imaging. A fever that keeps returning alongside your cough also falls into this category. These symptoms don’t necessarily mean something dangerous is happening, but they do require faster workup to rule out infections, structural problems, or growths in the lungs.