Coughing is a protective reflex triggered when sensory nerve endings in your airways detect something that shouldn’t be there. Whether it’s mucus, dust, stomach acid, or inflammation, the process follows the same basic pathway: irritation activates nerve fibers that send a signal through the vagus nerve to a cough center in your brainstem, which fires back a command to your chest and throat muscles to forcefully expel air. That burst of air can reach speeds of 15 m/s (about 33 mph), fast enough to clear debris from deep in your lungs.
How the Cough Reflex Works
Cough receptors line the surfaces of your throat, voice box, windpipe, and the branching airways of your lungs. Some respond to physical touch (a crumb going down the wrong pipe), while others detect chemical irritants (smoke, fumes, capsaicin from chili peppers). When triggered, these receptors send electrical impulses along branches of the vagus nerve to a coordinating region in the upper brainstem and pons. That region orchestrates the familiar three-phase sequence: a deep breath in, a brief closure of the vocal cords to build pressure, and an explosive release of air.
This entire process can also be influenced by higher brain centers, which is why you can suppress a cough in a quiet room or cough voluntarily. It’s a reflex, but not a completely automatic one.
Infections and the Common Cold
The most frequent reason people cough is a respiratory infection. Viruses that cause colds, flu, COVID-19, and bronchitis inflame the lining of the airways, making cough receptors far more sensitive than usual. Even normal airflow or a small amount of mucus that wouldn’t normally bother you can trigger repeated coughing during an infection.
This heightened sensitivity often outlasts the infection itself. A cough that lingers for two to four weeks after a cold is common because the airway lining takes time to heal and the nerve endings remain on edge. Bacterial infections like pneumonia and whooping cough also cause intense coughing, typically with thicker mucus or distinctive coughing fits.
Postnasal Drip and Sinus Problems
When your sinuses produce excess mucus from allergies, a sinus infection, or even cold dry air, that fluid drips down the back of your throat. This postnasal drip physically stimulates cough receptors in the throat and voice box. Over time, the constant contact between mucus and the delicate tissue of the pharynx can cause chronic inflammation, leaving the area red, swollen, and even more reactive to irritation. This cycle makes sinus-related coughs particularly stubborn, often worse at night when you’re lying down and gravity pulls secretions toward the back of the throat.
Acid Reflux
Stomach acid reaching places it doesn’t belong is one of the less obvious causes of a persistent cough. There are two ways this happens. First, acid that rises into the lower esophagus can trigger a nerve reflex. Because the esophagus and the airways share branches of the same vagus nerve, irritation in one area can activate coughing in the other, even if acid never reaches the throat. Second, small amounts of acid can travel all the way up and spill into the airway, a process called microaspiration. This directly irritates the lining of the throat and lungs. People with acid reflux-related cough often have no heartburn at all, which makes the connection easy to miss.
Asthma and Airway Inflammation
Asthma narrows and inflames the airways, and while most people associate it with wheezing and breathlessness, there’s a subset called cough-variant asthma where a dry cough is the only symptom. No wheezing, no chest tightness. The inflamed airways are hyperreactive, meaning they overrespond to triggers like cold air, exercise, or allergens by tightening and producing a persistent cough. Because the classic asthma symptoms are absent, cough-variant asthma is frequently misdiagnosed or overlooked for months.
Medications
A class of blood pressure drugs called ACE inhibitors causes a dry, nagging cough in roughly 2 to 11 percent of people who take them. The mechanism is well understood: these medications block an enzyme that normally breaks down a compound called bradykinin. When bradykinin accumulates in the airways, it sensitizes the nerve endings in the throat and lungs, making them fire more easily. The cough can start within weeks of beginning the medication or appear months later, and it resolves after switching to a different type of blood pressure drug.
Environmental and Chemical Irritants
Your airways have a receptor called TRPA1 that acts like a chemical alarm system. It binds to a wide range of irritants found in cigarette smoke, air pollution, cleaning products, and strong fragrances. Fine particulate matter (the tiny particles in smog and wildfire smoke, known as PM2.5) triggers inflammatory changes in the airway nerves that mirror what happens during an allergic reaction, making you cough even though there’s no infection.
People with chronic cough often find that their triggers extend well beyond obvious irritants. Perfume, cold air, exercise, stress, singing, and even talking can set off coughing fits. This is a sign of what researchers call cough hypersensitivity: the nerves in the airway have become so reactive that stimuli most people wouldn’t notice are enough to trip the reflex.
Wet Coughs vs. Dry Coughs
The distinction between a wet (productive) cough and a dry (nonproductive) cough tells you something about what’s going on inside. A wet cough brings up mucus and typically points to excess secretions in the airways, from infections, chronic bronchitis, or postnasal drip. A dry cough produces no mucus and is more often linked to nerve irritation: acid reflux, ACE inhibitors, cough-variant asthma, or lingering inflammation after a viral infection. Both types use the same reflex pathway, but they signal different underlying problems.
When a Cough Signals Something Serious
Most coughs are harmless and self-limiting. In adults, a cough that persists beyond eight weeks is classified as chronic and deserves investigation, while in children the threshold is four weeks. Certain accompanying symptoms raise the urgency considerably. Coughing up blood, unexplained weight loss, drenching night sweats, persistent hoarseness, difficulty swallowing, wheezing that doesn’t respond to treatment, and significant shortness of breath can all point to conditions ranging from chronic lung disease to malignancy. A fever that keeps returning alongside a cough may indicate an infection that isn’t clearing on its own.
The three most common causes of chronic cough in nonsmoking adults are postnasal drip, asthma, and acid reflux. In many cases, more than one of these is present at the same time, which is why a cough that doesn’t respond to treating just one cause often needs a broader approach.