A cough is a forceful burst of air from your lungs that clears your airways of mucus, irritants, and foreign particles. It’s one of the body’s most important protective reflexes, and it happens in three rapid stages: a deep breath in, a buildup of pressure in the chest against a closed throat, and a sudden opening that blasts air outward at high speed. Most coughs are harmless responses to temporary irritation, but a cough that lingers or comes with certain symptoms can signal something that needs attention.
How the Cough Reflex Works
Coughing isn’t something you consciously decide to do most of the time. It starts when specialized nerve endings detect something that shouldn’t be in your airways. These sensors are concentrated in the most vulnerable spots: the voice box, the windpipe, and the points where the large airways branch into smaller ones. When triggered, they send signals through branches of the vagus nerve to the brainstem, which coordinates the explosive muscle response.
What’s surprising is where else these cough-triggering nerves exist. They’re found in the ear canals, the eardrums, the sinuses, the lining around the heart, the diaphragm, and even the stomach and esophagus. This explains why seemingly unrelated problems, like acid reflux or an ear infection, can produce a persistent cough. Cleaning your ears with a cotton swab can trigger a coughing fit in some people because it stimulates a branch of the vagus nerve called Arnold’s nerve, which runs through the ear canal.
Wet Cough vs. Dry Cough
The simplest way to categorize a cough is by whether it produces mucus. A productive (wet) cough brings up phlegm and usually means your airways are generating extra mucus in response to infection, inflammation, or chronic lung conditions. A nonproductive (dry) cough produces no mucus and often feels like a tickle or irritation in the throat.
Dry coughs commonly accompany viral upper respiratory infections, allergies, and certain medications. One well-known culprit is a class of blood pressure drugs called ACE inhibitors, which can trigger a dry cough anywhere from one week to six months after starting the medication. The cough typically resolves within a few weeks of stopping the drug.
Wet coughs are more often linked to bacterial infections, bronchitis, pneumonia, and chronic conditions like bronchiectasis (permanently widened airways that accumulate mucus). The color and consistency of the mucus can offer clues: clear or white phlegm is common with viral infections and allergies, while thick, greenish-yellow phlegm often suggests a bacterial infection.
Acute, Subacute, and Chronic Cough
Doctors classify coughs by how long they last, using three time-based categories:
- Acute cough: lasts less than 3 weeks. This is the most common type, usually caused by a cold, flu, or other respiratory infection.
- Subacute cough: lasts 3 to 8 weeks. Often a lingering cough after an infection has cleared, sometimes called a post-infectious cough.
- Chronic cough: lasts longer than 8 weeks. This is the category that typically requires further investigation.
The 8-week threshold matters because it separates coughs that are almost certainly self-limiting from those likely driven by an ongoing condition. In adults, the most frequently identified drivers of chronic cough are asthma, postnasal drip (mucus from the sinuses draining down the back of the throat), and gastroesophageal reflux. In children, these three causes are actually far less common, and the diagnostic approach differs significantly. Pediatricians rely more heavily on the sound and quality of a child’s cough as a diagnostic clue, something that’s less useful in adults.
Common Causes
Short-term coughs are overwhelmingly caused by viral respiratory infections. The cold, flu, COVID-19, and RSV all irritate the airway lining and trigger coughing that may persist for a week or two after other symptoms resolve.
Beyond infections, coughing can result from inhaling irritants like smoke, dust, or chemical fumes. Allergies provoke coughing through the same inflammatory pathways that cause sneezing and a runny nose. Asthma narrows the airways and produces excess mucus, making coughing one of its hallmark symptoms, sometimes the only one.
Acid reflux is a less obvious cause. Stomach acid that travels up into the esophagus can irritate the nerve endings there and trigger a cough without any heartburn or obvious digestive symptoms. This is sometimes called “silent reflux” and can be difficult to identify because the connection between the stomach and the cough isn’t intuitive.
When a Cough Becomes Hypersensitive
Some people develop what’s known as cough hypersensitivity syndrome, where the cough reflex becomes overactive and fires in response to things that wouldn’t normally trigger it. Perfume, cold air, exercise, laughing, singing, or even talking can set off irresistible bouts of coughing. People with this condition often describe a persistent tickle or itch in the throat, along with a constant urge to cough.
This happens because the nerves involved in the cough reflex become sensitized, essentially lowering the threshold for what counts as an irritant. It can develop after a respiratory infection or alongside conditions like asthma and reflux. It’s increasingly recognized as its own clinical problem rather than just a symptom of something else, and it’s one of the more frustrating forms of chronic cough because standard treatments often don’t fully resolve it.
How Cough Medications Work
Over-the-counter cough remedies fall into two main categories that do opposite things. Cough suppressants reduce the urge to cough, while expectorants try to make coughing more productive.
The most common suppressant in nonprescription products works by raising the threshold for triggering a cough in the brainstem. It doesn’t eliminate the reflex entirely but makes it harder to activate. Another type, available by prescription, numbs the nerve endings in the airways so they stop sending “cough now” signals to the brain. For severe cases, opioid-based suppressants act on the brainstem directly, though their side effects and addiction potential limit their use.
Expectorants take the opposite approach. Rather than suppressing the cough, they aim to thin and loosen mucus so each cough is more effective at clearing the airways. The exact mechanism isn’t fully understood, but they appear to influence the glands that produce airway mucus. Mucolytics work similarly by breaking down the protein fibers in thick mucus, making it less sticky and easier to move.
Choosing between suppressing a cough and encouraging it depends on the type. Suppressing a productive cough can trap mucus in the lungs, which may slow recovery from an infection. Suppressing a dry, irritating cough that’s disrupting sleep or daily life is generally more appropriate.
Warning Signs to Watch For
Most coughs resolve on their own, but certain accompanying symptoms change the picture. Coughing up blood or pink-tinged phlegm, difficulty breathing or swallowing, and chest pain all warrant urgent evaluation. Choking or vomiting with a cough also calls for immediate attention.
A cough that persists beyond a few weeks, especially with thick greenish-yellow phlegm, wheezing, fever, shortness of breath, fainting, ankle swelling, or unexplained weight loss, points to something beyond a simple viral infection. Ankle swelling paired with a cough, for instance, can indicate heart failure, where fluid backs up into the lungs. Unexplained weight loss alongside a chronic cough raises concern for more serious lung conditions that benefit from early detection.