Sinus headaches are caused by inflammation and pressure buildup inside the air-filled cavities (sinuses) behind your forehead, cheeks, and eyes. The most common trigger is a viral upper respiratory infection, but allergies, structural blockages, and bacterial infections also play a role. Perhaps most important: roughly 80% of headaches that people believe are sinus headaches actually turn out to be migraines when formally evaluated, so understanding the real causes helps you get the right treatment.
Viral and Bacterial Infections
The single most common cause of a true sinus headache is a virus. The same rhinoviruses, influenza viruses, and coronaviruses that give you a cold also inflame the lining of your sinuses. When that lining swells, the narrow drainage openings get blocked, mucus accumulates, and pressure builds against the walls of the sinus cavities. That pressure is what you feel as pain across your forehead, between your eyes, or in your cheeks.
Most sinus infections stay viral and resolve on their own within a few weeks. Only a small percentage progress to bacterial infection. In children, who average more than six upper respiratory infections a year, about 6% to 13% of those viral cases develop into acute bacterial sinusitis. In adults the rate is lower, around 2%. When bacteria do take hold, the inflammation tends to worsen rather than improve after the first week, and you may notice thicker, discolored nasal discharge along with increasing facial pain.
Allergies and Chronic Inflammation
Allergic rhinitis (hay fever) is another major contributor. When you breathe in allergens like pollen, dust mites, or pet dander, the tissue inside your nose swells. That swelling can block the same sinus drainage pathways that infections block, trapping mucus and creating the familiar pressure and facial pain. Unlike an infection, allergy-driven sinus pressure tends to recur seasonally or persist as long as you’re exposed to the trigger.
Chronic inflammation from allergies also changes the environment inside the sinuses. The mucus becomes more acidic, which impairs the tiny hair-like structures (cilia) that normally sweep mucus out. Stagnant mucus then becomes a breeding ground for bacteria, which is why people with poorly controlled allergies are more prone to recurrent sinus infections and the headaches that come with them.
Structural Blockages
Some people get sinus headaches repeatedly because of the physical shape of their nasal passages. A deviated septum, where the wall between your nostrils is significantly off-center, can obstruct the openings where sinuses drain. Nasal polyps, enlarged turbinates, and other anatomical variations can do the same thing. When those openings are chronically narrowed, even mild swelling from a cold or allergen exposure is enough to seal them off completely.
Once drainage is blocked, the consequences cascade: ventilation inside the sinus drops, mucus stagnates, the local immune defenses weaken, and biofilms (stubborn colonies of bacteria) can form on the sinus walls. This is a primary pathway to chronic rhinosinusitis, defined as sinus inflammation lasting longer than 12 consecutive weeks. People with chronic rhinosinusitis often describe a persistent dull ache or pressure in the face rather than the sharp, intense pain of an acute infection.
Acute, Subacute, and Chronic Timelines
How long the headache lasts often reveals its cause. Acute rhinosinusitis, usually triggered by a virus, lasts less than four weeks. If symptoms continue past four weeks but resolve before 12 weeks, it’s considered subacute, and a bacterial component becomes more likely. Symptoms persisting beyond 12 weeks without a clear break point to chronic rhinosinusitis, which typically involves ongoing structural or inflammatory issues rather than a single infection.
This timeline matters practically. A sinus headache that arrives with cold symptoms and clears up in 10 days was almost certainly viral. One that gets worse after a week, especially with fever and worsening discharge, may have become bacterial. And one that never fully goes away likely has an underlying cause, such as allergies, polyps, or a deviated septum, that needs to be addressed separately from treating any infection.
Weather Changes and Barometric Pressure
Many people report that their sinus headaches flare when the weather shifts, and attribute this to changes in barometric pressure. The theory is that when atmospheric pressure drops, the air trapped in your sinuses expands and presses against inflamed tissue. While this mechanism is well-documented during large pressure swings like scuba diving or air travel (a condition called barosinusitis), research has not found evidence that the modest pressure changes from routine weather actually cause sinus inflammation. If your headaches reliably track with weather fronts, migraine is a more likely explanation, since migraine is well known to be triggered by atmospheric changes.
Why Most “Sinus Headaches” Are Actually Migraines
This is the finding that surprises most people. In a study of approximately 3,000 patients who described their headaches as sinus-related, either self-diagnosed or diagnosed by a physician, 80% actually met the formal criteria for migraine. The confusion happens because migraines frequently cause pain in exactly the same locations as sinus headaches: the forehead, around the eyes, and across the cheeks. Migraines also commonly trigger nasal congestion, a runny nose, and watery eyes, all of which feel like sinus symptoms.
The key differences are subtle but important. A true sinus headache almost always comes with signs of an active infection or allergic flare: thick, discolored nasal discharge, reduced sense of smell, and often a fever. If your headache comes with clear nasal drainage (or no drainage at all), sensitivity to light or sound, nausea, or pain that throbs and worsens with physical activity, migraine is far more likely. This distinction matters enormously because the treatments are completely different. Decongestants and saline rinses won’t help a migraine, and migraine-specific treatments won’t clear a sinus infection.
How To Tell It’s a True Sinus Headache
A genuine sinus headache has a few hallmarks that set it apart:
- Nasal discharge that’s thick and discolored (yellow or green), not clear and watery
- Pain that worsens when you bend forward or press on the affected sinus area
- Recent cold symptoms that either haven’t resolved or got better and then worsened again
- Reduced or absent sense of smell
- Pain localized to one side or concentrated over specific sinuses, rather than a generalized headache
If you’re missing most of these features but still experiencing recurring facial pain and pressure, the headache is more likely to be a migraine or tension-type headache. The International Headache Society specifically notes that both migraine and tension-type headache are commonly mistaken for sinus headaches because the pain locations overlap so closely. Getting the right diagnosis can mean years of better treatment. One study described the misdiagnosis as “a delay that can last for many years,” during which patients cycle through rounds of antibiotics and decongestants that never fully help.
When Sinus Headaches Signal Something Serious
Most sinus headaches are uncomfortable but not dangerous. However, because the sinuses sit close to the eyes and brain, infections can occasionally spread to surrounding structures. Warning signs that a sinus headache has become something more serious include swelling or redness around one eye, vision changes, a severe headache that feels different from previous episodes, high fever, confusion, or a stiff neck. These symptoms can indicate that infection has moved beyond the sinuses into the eye socket or toward the brain, both of which require urgent medical attention.