A cough starts with sensory nerve endings buried in the lining of your airways, primarily in the throat, windpipe, and the point where your airways first branch into the lungs. When something irritates those nerve endings, they fire a signal up to a coordination center in your brainstem, which then commands your chest, diaphragm, and abdominal muscles to produce the explosive burst of air you experience as a cough. The whole sequence, from irritation to cough, takes a fraction of a second.
Where the Sensors Live
Your airways are lined with specialized nerve fibers that act as an alarm system. These fibers are branches of the vagus nerve, a major nerve that runs from your brainstem down through your chest and abdomen. The most sensitive spots for triggering a cough are the voice box (larynx), the windpipe (trachea), and the points where your airways fork into smaller branches. These areas respond strongly to both physical touch and chemical irritation.
Interestingly, your smaller airways deeper in the lungs also play a role. Studies in human volunteers show that inhaling an irritant in tiny droplets, which travel deeper into the lungs, actually triggers coughing more easily than larger droplets that land higher up. So while the main alarm sensors sit in the upper airways, the deeper tissue can be even more chemically sensitive.
How Your Nerves Detect Irritants
The nerve endings in your airways contain ion channels that work like molecular locks. Different irritants act as keys. One type of channel responds to capsaicin (the compound that makes chili peppers burn), acid, and heat. Another type responds to a broader range of environmental irritants: acrolein from cigarette smoke and car exhaust, ozone from air pollution, and even cinnamaldehyde, the compound that gives cinnamon its bite. These channels also detect cold air and inflammatory chemicals your own body produces during infection or allergic reactions.
When an irritant activates these channels, calcium floods into the nerve cell, generating an electrical signal. That signal races up the vagus nerve to your brainstem. This is why so many different things can make you cough: smoke, dust, cold air, spicy food, a tickle in your throat. They all converge on the same set of molecular sensors.
The Three Phases of a Cough
Once your brainstem’s cough center receives the alarm signal, it coordinates a precise three-phase response. First comes the inspiratory phase: you inhale, pulling air into your lungs to stretch your chest muscles into a position where they can contract powerfully. Second is the compressive phase, lasting only about 200 milliseconds. Your vocal cords snap shut, sealing the airway while your chest and abdominal muscles contract hard against the trapped air, building pressure like a pressurized canister. Third, your vocal cords open suddenly and the compressed air blasts out.
That blast is remarkably forceful. Measurements of cough velocity show air leaving the mouth at an average of about 15 meters per second in men and 13 meters per second in women, roughly 30 to 34 miles per hour. Peak speeds in some individuals reach 29 meters per second, over 60 miles per hour. Each cough can expel saliva droplets more than 2 meters (about 6.5 feet) from your mouth.
What a Cough Is Actually Clearing
Your airways constantly produce a thin layer of mucus, around 30 milliliters per day in a healthy person. This mucus is made by secretory cells scattered throughout the airway lining and by small glands embedded in the walls of your larger airways. It works as a sticky trap: inhaled dust, bacteria, pollen, and dissolved chemicals get caught in the mucus gel.
Normally, tiny hair-like structures called cilia beat in coordinated waves, pushing the mucus upward toward your throat like a slow escalator. Once it reaches the top of the windpipe, it passes through the voice box into the throat and gets swallowed without you noticing. Your vocal cords, which are covered by a different type of tissue that doesn’t have cilia, can’t participate in this conveyor system. Instead, they contribute to cough clearance by sealing shut to build pressure.
Coughing is the backup system. When mucus production increases (during a cold or bronchitis, for example) or when the cilia are damaged (from smoking or infection), the escalator can’t keep up. A cough generates enough airflow force to shear mucus off the airway walls and propel it upward. This is what produces a “wet” or productive cough. A dry cough, by contrast, involves the same reflex but is driven by irritation or inflammation rather than excess mucus.
Surprising Sources of a Cough
Not every cough originates from something in your lungs or throat. The vagus nerve branches into your esophagus, stomach, and even your ear canal, which means irritation in those areas can trigger coughing too.
Post-nasal drip is one of the most common non-lung triggers. When excess mucus from your sinuses drips down the back of your throat, it physically stimulates cough receptors in the voice box and the area just above it. Research in animal models confirms this is a mechanical trigger: the dripping fluid itself activates nerve fibers, producing a cough signal even without any infection in the lungs.
Acid reflux (GERD) is another major cause, and it works through two routes. Acid that travels far enough up the esophagus can directly irritate the throat and voice box. But even reflux that stays in the lower esophagus can cause coughing through a reflex loop: acid activates receptors in the esophageal lining, which share a nerve pathway with the airways. The brainstem interprets this signal and triggers a cough, even though nothing has actually entered the lungs. Both acidic and non-acidic reflux can do this, which is why some people with reflux-related coughs don’t experience heartburn. Non-acidic reflux appears to activate mechanical stretch receptors in the esophagus, while acidic reflux activates chemical receptors on vagus nerve endings.
Acute, Subacute, and Chronic Coughs
Clinicians categorize coughs by how long they last. An acute cough lasts fewer than 3 weeks and is usually caused by a cold, flu, or other upper respiratory infection. A subacute cough lasts 3 to 8 weeks, often lingering after an infection has cleared because the airway lining remains inflamed and hypersensitive. A chronic cough persists beyond 8 weeks.
Chronic coughs have a different set of usual suspects. The three most common causes in adults are post-nasal drip from sinus problems, asthma (particularly a variant that produces coughing rather than wheezing), and acid reflux. In many chronic cough cases, the underlying problem isn’t ongoing damage but rather a cough reflex that has become overly sensitive. The same nerve channels that detect irritants get “turned up,” so normal stimuli like talking, laughing, temperature changes, or even mild scents can set off a coughing episode.
Signs a Cough Needs Attention
Most coughs resolve on their own, but certain features signal something more serious. Coughing up blood, even small amounts, needs prompt evaluation to rule out conditions like a pulmonary embolism or pneumonia. The same goes for a cough accompanied by significant breathlessness, chest pain that worsens with breathing, a high or prolonged fever, or bluish discoloration of the lips or fingertips. Difficulty swallowing alongside a cough can suggest a structural problem or a foreign body. Any cough lasting 3 weeks or longer without improvement warrants a medical evaluation, particularly in smokers or former smokers.