A cough is a three-phase explosion of air that your body can trigger automatically or that you can perform on command. It starts with a quick inhale, follows with a brief moment of intense pressure buildup behind closed vocal cords, and finishes with a forceful blast of air that can reach speeds above 30 miles per hour. The whole sequence takes less than a second, but it involves a surprisingly coordinated effort between your brain, nerves, muscles, and airways.
The Three Phases of a Cough
Every cough, whether it’s a deliberate throat-clearing or a reflexive hack from inhaling dust, follows the same basic pattern: inhale, compress, expel.
In the first phase, you take in a quick breath. This isn’t just about filling the lungs with air to push out. The inhale stretches your expiratory muscles (the ones that will do the pushing), putting them at an optimal length to generate maximum force. Think of it like pulling back a slingshot before releasing it.
In the second phase, your vocal cords snap shut, sealing the airway at the level of the voice box. At the same time, your abdominal and chest wall muscles contract hard against that sealed airway. This compressive phase lasts only about 200 milliseconds, but it builds enormous pressure inside your chest. The pressure generated typically ranges between 50 and 250 mmHg, which is high enough that it gets transmitted into your blood vessels and can temporarily affect your heart rate and blood pressure.
In the third phase, the vocal cords fly open and all that pressurized air rushes out. Studies measuring cough airflow found that the average peak velocity is about 15 meters per second in men and 13 meters per second in women, roughly 30 to 34 miles per hour. That high-speed airstream is what dislodges mucus, dust, food particles, or whatever else triggered the cough in the first place.
Which Muscles Power a Cough
Normal breathing out is mostly passive. Your lungs and chest wall simply recoil back to their resting position, like a stretched rubber band returning to shape. Coughing is a different story. It requires active, forceful contraction from multiple muscle groups working together.
The primary drivers are your abdominal muscles: the rectus abdominis (the “six-pack” muscle), the external and internal obliques along your sides, and the transversus abdominis, the deepest layer that wraps around your torso like a corset. These muscles compress the abdominal cavity, which pushes the diaphragm upward and forces air out of the lungs. The internal intercostal muscles between your ribs also contract, pulling the rib cage inward and downward to shrink the chest cavity further.
This is why coughing can make your abs sore after a bad cold, and why people with weak abdominal muscles (after surgery, spinal cord injury, or certain neurological conditions) often have trouble coughing effectively. Without strong compression, you can’t build the pressure needed to clear your airways.
How the Cough Reflex Gets Triggered
Your airways are lined with specialized nerve endings that act as sensors. These sensors, carried by branches of the vagus nerve, sit in the mucous membrane from your throat all the way down to the smallest airways deep in your lungs. Two main types of nerve fibers are involved: one type responds to mechanical touch and stretch (like a crumb hitting the back of your throat), and another type responds to chemical irritants (like capsaicin in hot peppers, smoke, or stomach acid).
When these sensors detect something that shouldn’t be there, they fire signals along the vagus nerve up to the brainstem. The brainstem processes the signal and sends commands back out to the muscles of the diaphragm, chest wall, abdomen, and voice box, coordinating the entire cough sequence automatically. You don’t have to think about it any more than you think about pulling your hand off a hot stove.
You Can Also Cough on Purpose
Unlike many reflexes, coughing isn’t purely automatic. You can cough whenever you want to, and you can also suppress a cough (at least partially) when the reflex fires at an inconvenient time. This dual control reflects the fact that coughing involves brain regions beyond just the brainstem.
The traditional view held that cough was a simple brainstem reflex, but newer research shows the cough circuitry extends into widespread areas of the cortex and subcortical brain, the same regions involved in conscious decision-making, sensation, and motor planning. This is why you can voluntarily clear your throat before a speech, and also why emotional states, attention, and even placebo treatments can influence how much you cough. It’s a reflex with a volume knob that your higher brain can turn up or down.
Wet Coughs vs. Dry Coughs
The mechanical action is the same in both cases. The difference is what triggers the cough and what comes out. A productive (wet) cough is doing exactly what the cough reflex evolved to do: moving mucus up and out of the airways. When you’re sick with a respiratory infection, your airways produce extra mucus to trap germs and debris. The cough clears that mucus, and you’ll feel or hear the congestion as it moves.
A nonproductive (dry) cough produces no mucus. It’s typically triggered by irritation or inflammation in the airways rather than by mucus buildup. Dry coughs are common with viral infections that inflame the throat lining, exposure to irritants like smoke, acid reflux irritating the upper airway, or conditions like asthma. The cough reflex keeps firing because the sensors in your airways remain irritated, even though there’s nothing to clear out. This makes dry coughs particularly frustrating since they serve no useful purpose but can be hard to stop.
Why Cough Strength Matters
An effective cough depends on generating enough airflow to actually move material out of the airways. Several things can weaken the chain. If you can’t take a deep enough breath in phase one, you won’t stretch the muscles properly or fill the lungs with enough air. If the vocal cords can’t close completely (due to nerve damage or a breathing tube, for example), you can’t build adequate pressure in phase two. If the abdominal or chest muscles are weak, phase three won’t produce enough force.
This is why respiratory therapists teach assisted cough techniques to people recovering from surgery or living with neuromuscular conditions. Some techniques involve manually pressing on the abdomen during the expulsive phase to compensate for weak muscles. Others use devices that mechanically simulate the pressure changes of a cough. The goal is always the same: replicate that rapid three-phase sequence that healthy lungs perform effortlessly dozens of times a day.