Your eyes water during a headache because of a reflex arc connecting your pain-sensing nerves to the glands that produce tears. When the trigeminal nerve, the main nerve responsible for sensation in your face, gets activated by head pain, it can trigger a parasympathetic response that stimulates your tear glands, nasal lining, and blood vessels on the same side as the pain. This is called the trigeminoparasympathetic reflex, and it explains why tearing, a stuffy nose, and facial flushing so often travel together during a headache.
The Nerve Reflex Behind the Tearing
The trigeminal nerve runs across your forehead, cheeks, and jaw. When pain signals fire through its upper branches, they loop through a relay station in the brainstem called the superior salivatory nucleus. From there, signals travel out through parasympathetic nerve fibers to a small cluster of nerve cells behind your nose called the sphenopalatine ganglion, the largest parasympathetic hub outside the brain in your head. This ganglion sends instructions to your tear glands, nasal membranes, and the blood vessels in your face.
The result: your eyes water, your nose runs or stuffs up, your eyelid may droop, and the skin on that side of your face can flush and sweat. All of these symptoms tend to appear on the same side as the pain because the reflex follows the nerve pathway on that side only. The hypothalamus, a brain region involved in regulating automatic body functions, also modulates this reflex. In some headache conditions, the reflex appears to be pathologically “disinhibited,” meaning the brain’s normal braking system on parasympathetic activity fails, letting the tearing and congestion run unchecked.
It Happens in Migraines More Than People Realize
Tearing during a headache is often associated with rare headache types, but it is surprisingly common in ordinary migraines. In one study published in The Journal of Headache and Pain, 74% of migraine patients reported at least one autonomic symptom during attacks. Tearing was the most frequently reported, occurring in about 31% of migraine sufferers. Nasal congestion (32%) and a feeling of fullness in the ears (25%) were close behind.
This matters because many people with migraine get misdiagnosed with sinus headaches when their main complaints are watery eyes and a stuffy nose. Researchers have emphasized that these autonomic symptoms can occur in migraine and should not steer clinicians away from a migraine diagnosis. If your headaches come with light sensitivity, nausea, or throbbing pain on one side and also make your eyes water, migraine is a likely explanation.
Cluster Headaches and Severe Tearing
Cluster headaches produce the most dramatic eye watering. These attacks bring severe, stabbing pain around one eye, typically lasting 15 minutes to three hours, and strike in clusters over weeks or months. The autonomic symptoms are intense and hard to miss: excessive tearing, a bright red eye, a droopy eyelid, a runny or blocked nose, and facial sweating, all on the same side as the pain.
The tearing in cluster headaches is driven by the same trigeminoparasympathetic reflex, but the activation is far stronger than in migraine. Research shows elevated levels of signaling molecules associated with both the trigeminal nerve and the parasympathetic system during cluster attacks. Successful treatment, whether with oxygen or specific medications, normalizes these chemical markers, confirming that the reflex is directly tied to the attack itself.
Less Common Headache Types Defined by Tearing
Some rare headache conditions are actually diagnosed based on the presence of tearing. SUNCT (short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing) is named specifically for the combination of eye redness and tearing that accompanies brief, severe stabs of pain around the eye. These attacks last seconds to minutes but can strike 20 to 200 times a day. A related condition, SUNA, involves similar pain with other autonomic features but without both eye redness and tearing together.
Paroxysmal hemicrania is another headache in this family. It causes short, severe one-sided attacks with prominent tearing and nasal congestion, occurring multiple times daily. It has a distinctive feature: it responds completely to a specific anti-inflammatory medication, to the point where that response is part of the diagnostic criteria. Hemicrania continua, a continuous one-sided headache, also produces autonomic symptoms like tearing during pain flare-ups, sometimes with a sensation of something in the eye on the affected side.
Other Causes Worth Considering
Not all headaches with tearing come from a primary headache disorder. Sinus infections cause pressure and pain across the forehead and cheeks along with watery or mucus-filled drainage. Eye strain from prolonged screen time can trigger both a dull headache and reflex tearing. Acute angle-closure glaucoma produces a painful, red, watery eye with a severe headache and is a medical emergency.
Rarely, a tear in a blood vessel wall in the neck (carotid or vertebral artery dissection) can cause headache with facial pain and autonomic symptoms that mimic cluster headache. This is more likely if the headache came on suddenly, feels unlike any headache you have had before, or followed neck trauma.
Patterns That Warrant Medical Attention
A headache paired with a painful red eye is specifically listed as a warning sign by Harvard Health. Other patterns that deserve prompt evaluation include headaches that started for the first time after age 50, a sudden severe headache unlike anything you have experienced, headaches that worsen with coughing or movement, and head pain accompanied by fever, stiff neck, confusion, or neurological changes like vision loss or slurred speech.
If your eyes water with every headache and the pattern has been consistent for months or years, you are most likely experiencing the trigeminoparasympathetic reflex in the context of migraine or another primary headache disorder. Tracking the details helps: how long each episode lasts, whether the tearing is on one side or both, and what other symptoms appear alongside it. These specifics are exactly what a neurologist uses to distinguish between migraine, cluster headache, paroxysmal hemicrania, and the rarer conditions, each of which responds to different treatments.