When you cough, your body executes a rapid, coordinated sequence that blasts air out of your lungs at speeds exceeding 30 miles per hour. It happens in three distinct phases, all unfolding in less than a second, and involves your diaphragm, chest muscles, vocal cords, and a network of nerve sensors lining your airways. What feels like a simple reflex is one of the most forceful things your body does on a routine basis.
How a Cough Happens in Three Phases
Every cough follows the same three-step pattern: inhale, compress, explode.
In the first phase, you inhale a large volume of air. This deep breath stretches out the muscles between your ribs and your diaphragm, loading them like a spring so they can contract with maximum force. The amount of air you draw in varies depending on the cough, but this initial breath is what gives a cough its power.
In the second phase, your vocal cords snap shut, sealing off your airway at the level of your throat. Your chest and abdominal muscles then contract hard against that sealed airway, building up enormous pressure inside your chest cavity. This compression phase is remarkably brief, lasting only about 200 milliseconds. During that fraction of a second, pressure inside your chest can spike dramatically.
In the third phase, your vocal cords fly open and all that pressurized air rushes out at high velocity. Measurements using particle imaging show that air exits the mouth at average peak speeds around 15 meters per second for men and 13 meters per second for women, roughly 30 to 34 miles per hour. That blast of air is what carries mucus, dust, and other irritants up and out of your airways.
What Triggers the Reflex
The cough reflex starts with specialized nerve endings embedded in the lining of your airways. Two main types of sensors do the detecting. One type responds to physical touch and stretching, firing when something like a crumb, dust particle, or pooled mucus physically contacts the airway wall. The other type responds to chemical irritants: things like cigarette smoke, strong fumes, stomach acid that creeps up from reflux, or the inflammatory chemicals your own immune system releases during an infection.
Both types of sensors send their signals to the brain through branches of the vagus nerve, a long nerve that runs from your brainstem down through your chest and abdomen. Those signals land in a specific relay station in the lower brainstem, where the brain processes the information and fires back a coordinated command to your breathing muscles, diaphragm, and vocal cords. This entire loop, from irritation to cough, happens automatically. You can suppress it briefly with effort, or trigger a voluntary cough, but the reflex itself doesn’t require any conscious thought.
Why Your Body Coughs
Coughing is primarily a defense mechanism. Your airways are constantly producing a thin layer of mucus that traps inhaled particles, bacteria, and viruses. Tiny hair-like structures called cilia beat rhythmically to push that mucus upward toward your throat, where you swallow it without noticing. This cleanup system works well under normal conditions, but when mucus production increases (during a cold, for example) or when something irritating enters the airway too quickly for cilia to handle, coughing takes over.
The high-speed airflow of a cough clears mucus through what physicists call two-phase gas-liquid flow. Essentially, the fast-moving air grabs the slower-moving layer of mucus on the airway surface and drags it upward, the same way wind creates waves on water. When mucus is thick or plentiful, as it is during bronchitis or pneumonia, this shearing mechanism becomes the dominant way your lungs stay clear. In healthy lungs with only a thin mucus layer, the rushing air may also stimulate the cilia to beat faster, boosting the normal cleanup process even after the cough ends.
What Happens to the Rest of Your Body
A cough doesn’t just affect your lungs. The pressure spike inside your chest during the compression phase ripples through your entire cardiovascular system. Intrathoracic pressure during a forceful cough can push systolic blood pressure above 220 mmHg, far higher than normal resting levels of around 120. This is a momentary surge that healthy blood vessels handle without trouble, but it explains why hard coughing can make you feel lightheaded or see spots.
Your abdominal muscles contract forcefully during every cough, which temporarily increases pressure in your abdomen as well. This is why a bad coughing fit can leave your stomach muscles sore the next day, and why prolonged coughing sometimes leads to stress urinary incontinence, particularly in women, when that abdominal pressure overwhelms the pelvic floor.
When Coughing Itself Causes Problems
An occasional cough is harmless and helpful. Repeated, forceful coughing over days or weeks is a different story. The Mayo Clinic lists a range of complications tied to chronic coughing: sleep disruption, headaches, dizziness, excessive sweating, vomiting, urinary incontinence, fainting (called cough syncope), and even broken ribs. Rib fractures from coughing are uncommon in young, healthy people but become a real risk in older adults or anyone with lower bone density.
Cough syncope, where someone briefly passes out during a coughing fit, happens because the extreme chest pressure temporarily reduces blood flow back to the heart. With less blood returning, the heart has less to pump to the brain, and consciousness flickers. People who experience this tend to be coughing while standing, and the episodes resolve on their own within seconds, but they can be dangerous if they cause a fall.
Acute, Subacute, and Chronic Cough
Doctors categorize coughs by how long they last, because duration is one of the most useful clues to the underlying cause. A cough lasting less than three weeks is considered acute and is most often caused by a cold, flu, or other upper respiratory infection. A cough persisting for three to eight weeks falls into the subacute category, which commonly represents the tail end of a respiratory infection where the airways remain irritated even after the infection itself has cleared.
A cough lasting longer than eight weeks is classified as chronic. At that point, the most common culprits shift away from infections and toward conditions like postnasal drip, asthma, and gastroesophageal reflux, where stomach acid irritates the lower esophagus and sometimes the airway itself. Some blood pressure medications can also cause a persistent dry cough as a side effect. A cough that crosses the eight-week threshold is worth investigating, because it usually points to an ongoing, treatable condition rather than something that will resolve on its own.