Sneezing originates from a specialized group of sensory nerve cells lining the inside of your nose. When these cells detect an irritant, they fire a signal to a coordination center in the lower part of your brain, which then orchestrates a rapid, full-body expulsion of air. The entire process, from the first tickle to the explosive exhale, is an involuntary reflex your body uses to blast foreign particles out of your airways before they can reach your lungs.
The Nerve Cells That Start It All
The inside of your nose is packed with sensory nerve endings that belong to the trigeminal nerve, one of the largest nerves in your head. These endings detect mechanical pressure, temperature changes, and chemical irritants through specialized receptors on their surface. But not all of them can trigger a sneeze. A 2024 study published in Cell identified a single, specific population of sensory neurons responsible for sneezing. These neurons express a particular receptor (called MrgprC11) and are the only ones that respond to the full range of sneeze triggers: nasal irritants, allergens, and viruses.
These sneeze-specific neurons also use a heat- and chemical-sensing channel called TRPV1, which is broadly present across nasal sensory neurons. TRPV1 is the same receptor that detects capsaicin, the compound that makes chili peppers burn. That’s why spicy food can make you sneeze: it’s literally activating the same receptor pathway that pollen or dust would.
How Your Brain Coordinates the Sneeze
Once those nasal neurons fire, their signal travels along the ethmoidal nerve (a branch of the trigeminal) to a region in the medulla, the lowest part of your brainstem, just above where your spinal cord begins. Neuroimaging research has confirmed the existence of a “sneeze center” in the rostral medulla, near a structure called the spinal trigeminal nucleus. This area acts as a command hub, collecting incoming irritation signals and, once they cross a certain threshold, launching the sneeze.
The sneeze center doesn’t just relay a single command. It coordinates a precise sequence of events across your chest, throat, and face muscles, all within a fraction of a second. Electrical stimulation of the ethmoidal nerve in lab settings reliably triggers the full sneeze reflex, confirming that this pathway is the ignition switch. Interestingly, sneezing and coughing use different central pathways in the brain, even though both are expulsive reflexes designed to clear your airways. That’s why a cough medication won’t stop your sneezes.
The Three Phases of a Sneeze
A sneeze unfolds in three rapid stages. First, in the inspiratory phase, you take a deep, involuntary breath. Your diaphragm contracts and your chest expands, pulling a large volume of air into your lungs. This is the familiar “ahh” before the “choo.”
Next comes a brief closure phase. Your vocal cords snap shut and your tongue presses against the roof of your mouth, momentarily trapping all that air under rising pressure in your chest.
Then the expulsive phase hits. Your diaphragm, abdominal muscles, and the muscles between your ribs all contract forcefully at once, blasting air upward through your reopened airway. This phase demands significantly more muscular force than normal breathing. Research on diaphragm function shows that while regular breathing recruits only slow, fatigue-resistant muscle fibers, sneezing requires the activation of much stronger, faster-fatiguing motor units. That’s why a hard sneeze can feel physically exhausting, and why people with weakened diaphragm muscles sometimes struggle to clear their airways effectively.
How Fast and Far a Sneeze Travels
Experimental measurements using particle imaging show that sneeze airflow reaches a peak velocity of about 15.9 meters per second, roughly 35 miles per hour. The spray fans out at an angle of about 15 degrees both vertically and horizontally from the nose and mouth. Smaller droplets can become aerosolized and linger in indoor air, while larger droplets follow a ballistic arc and settle on surfaces. This is why covering your sneeze matters so much for preventing the spread of respiratory infections.
Why We Sneeze at All
Sneezing is a protective reflex with a clear evolutionary purpose. That powerful burst of air physically ejects irritants, pathogens, and debris from your nasal passages before they can travel deeper into your lungs, where infections are harder to fight. This isn’t just a mechanical cleaning process. Sneezing also ties into your immune response: when your body detects a virus or allergen in the nasal lining, the sneeze reflex works alongside local inflammation and mucus production to trap and expel the threat. It’s a first line of defense, keeping harmful particles from reaching the lower respiratory tract where they could cause pneumonia or bronchitis.
Unusual Sneeze Triggers
Not all sneezes come from dust or pollen. Some people sneeze when they step into bright sunlight, a phenomenon called the photic sneeze reflex (sometimes nicknamed ACHOO syndrome). About one in four people who already feel a nasal prickle will sneeze in response to sunlight, though “pure” photic sneezing triggered by light alone is far less common. The trait runs in families as an autosomal dominant trait, meaning you only need one copy of the gene variant from one parent to inherit it. The exact gene responsible hasn’t been identified yet, but the leading theory is that the optic nerve’s proximity to the trigeminal nerve allows bright light signals to “leak” into the sneeze pathway.
Eating can also trigger sneezing, particularly spicy or very hot foods. This is related to gustatory rhinitis, where heat or spice compounds activate the trigeminal nerve in your nasal membranes, producing a runny nose and sometimes a full sneeze. Some people sneeze after eating large meals regardless of spiciness, likely through vagal nerve stimulation from a full stomach putting pressure on adjacent nerve pathways.
Why You Can’t Sneeze in Your Sleep
You might have noticed you never sneeze while fully asleep, and that’s not a coincidence. During sleep, the brainstem raises the threshold of stimulation needed to trigger a sneeze. The part of your brain responsible for detecting nasal irritation is essentially turned down. If mucus or an irritant accumulates in your nose overnight, it just sits there because the protective reflex isn’t active. If the stimulus is strong enough, say a particularly potent allergen, it will actually wake you up first, and then you’ll sneeze. You cannot sneeze through genuine sleep; the reflex requires a waking level of brain activity to fire.
Containing the Spread
Given that a sneeze launches droplets at 35 mph, proper coverage makes a real difference in limiting respiratory disease transmission. The CDC recommends covering your mouth and nose with a tissue, then immediately throwing it away. If no tissue is available, sneeze into the inside of your elbow rather than your hands, since your hands touch shared surfaces constantly throughout the day. Wash your hands with soap and water for at least 20 seconds afterward. When soap isn’t available, hand sanitizer with at least 60% alcohol is the next best option.