A sinus infection, medically called sinusitis, happens when the air-filled spaces behind your forehead, cheeks, nose, and eyes become inflamed and swollen. That swelling traps mucus that would normally drain freely, creating a warm, moist environment where bacteria or viruses thrive. It’s one of the most common reasons people visit a doctor, accounting for 2.7 million physician office visits in the United States in 2018 alone.
How a Sinus Infection Develops
Your sinuses are lined with a thin layer of tissue that produces mucus. Under normal conditions, that mucus drains through narrow openings into your nasal passages, keeping the sinuses clean and humidified. When something triggers inflammation in that lining, whether a cold virus, allergies, or an irritant, the tissue swells and those drainage channels narrow or close off entirely.
Once mucus is trapped, it stagnates. Bacteria that are normally present in small, harmless numbers can multiply rapidly in the blocked fluid. The result is pressure, pain, and the thick, discolored discharge most people associate with a sinus infection. The location of the blockage determines where you feel it: the sinuses sit behind your forehead, between your eyes, in your cheekbones, and deep behind the nasal cavity near the base of your skull.
Viral vs. Bacterial: How to Tell the Difference
Most sinus infections start as viral infections, essentially a common cold that settles into the sinuses. These typically improve on their own within 7 to 10 days. A bacterial sinus infection is less common but more stubborn, and it often follows a pattern doctors call “double sickening”: your cold symptoms start to improve, then suddenly get worse again with a new wave of congestion, facial pain, or fever.
Green or yellow nasal discharge on its own doesn’t automatically mean bacteria are involved. However, the combination of colored discharge, disrupted sleep, and more severe symptoms does shift the odds toward a bacterial cause. Mild symptoms without significant nasal discharge point more toward a simple upper respiratory infection that will resolve without antibiotics.
Acute, Subacute, and Chronic Types
Sinus infections are classified by how long they last. Acute sinusitis lasts less than 2 weeks and is the most common type, usually triggered by a cold. Subacute sinusitis lingers between 2 weeks and 3 months, often because the initial infection wasn’t fully cleared or an underlying issue like allergies keeps fueling inflammation. Chronic sinusitis persists beyond 3 months without returning to baseline. It may involve ongoing low-grade infection, structural problems like nasal polyps, or a cycle of inflammation that sustains itself even after the original trigger is gone.
Chronic sinusitis feels different from an acute infection. Instead of sharp pain and high fever, people often describe a constant sense of facial fullness, reduced sense of smell, fatigue, and a postnasal drip that never fully clears. It significantly affects quality of life and often requires a different treatment approach than a straightforward acute episode.
Where the Pain Shows Up
The specific location of your pain and pressure can hint at which sinuses are affected. Infection in the maxillary sinuses (behind the cheekbones) tends to cause facial pain on one side, sometimes radiating to the upper teeth. Frontal sinus infections produce tenderness and pressure across the forehead, particularly along the inner edge of the eyebrow where the bone is thinnest. Fever is more common with frontal involvement.
Sphenoid sinusitis, which affects the sinuses deep behind the nose near the center of the skull, is uncommon but causes pain at the top of the head or radiating to the temples. It can feel like a whole-head ache rather than the localized pressure of other types. The ethmoid sinuses, located between the eyes, often cause pain and pressure at the bridge of the nose and behind the eyes.
Common Causes and Risk Factors
The common cold is the single biggest trigger. Allergies are a close second, because the same swelling that makes your nose stuffy from pollen or dust can block sinus drainage. Other risk factors include a deviated septum or nasal polyps (both of which physically narrow the drainage pathways), smoking, frequent swimming, and a weakened immune system.
When bacterial infection does set in, the most common culprits are two species that also cause ear infections and pneumonia. A third bacterium commonly found in children rounds out the top three. These organisms are already present in the nasal passages of many healthy people and only cause trouble when trapped mucus gives them the opportunity to overgrow.
How It’s Diagnosed
For a straightforward sinus infection, your doctor doesn’t need imaging. Uncomplicated sinusitis is diagnosed based on your symptoms and a physical exam. The key findings, including facial tenderness, swollen nasal tissue, and discolored discharge, are enough for most cases.
CT scans and other imaging are reserved for situations where treatment isn’t working, symptoms keep coming back, or there’s concern about a complication like infection spreading beyond the sinuses. If you’ve been treated for chronic or recurrent sinusitis without improvement, a CT scan helps map the anatomy of your sinuses and guide decisions about whether surgery might help.
Treatment and Home Care
Since most acute sinus infections are viral, the first line of treatment is managing symptoms while your body fights off the infection. Saline nasal rinses are one of the most effective home remedies and have solid scientific backing. Flushing the nasal passages with salt water washes out trapped mucus and allergens, hydrates the sinus lining, and helps the tiny hair-like structures in your sinuses (cilia) move mucus more efficiently. Hypertonic saline, which is slightly saltier than your body’s own fluids, works better than regular saline at improving this clearance. You can use a squeeze bottle or neti pot with distilled or previously boiled water.
Over-the-counter decongestant sprays can open up the drainage pathways, but using them for more than 3 days can cause rebound congestion that makes things worse. Oral decongestants, pain relievers, and steam inhalation also help with comfort. For allergic triggers, antihistamines or nasal steroid sprays address the underlying inflammation.
Antibiotics only make sense when a bacterial infection is likely: symptoms lasting more than 10 days without improvement, a clear “double sickening” pattern, or unusually severe symptoms like high fever and intense facial pain from the start. When antibiotics are prescribed, it’s important to complete the full course even if you feel better partway through.
When Sinus Infections Become Serious
Complications from sinusitis are rare, but they can be severe because of where the sinuses sit in your skull. The eye sockets share thin walls with the sinuses, and orbital involvement accounts for roughly 80% of all sinusitis complications. Infection can spread to the tissue around the eye, causing swelling, redness, pain with eye movement, and in serious cases, vision changes. This requires urgent treatment.
Intracranial complications, such as brain abscesses or infection of the membranes surrounding the brain, occur in about 4% of patients who develop complications. Frontal sinus infections pose the highest risk because of the frontal lobe’s proximity. Sinusitis is estimated to be the underlying cause of 10% of all brain abscesses. Warning signs include severe headache, high fever, visual changes, swelling around the eyes, or altered mental state. These situations are medical emergencies, but they’re genuinely rare for the vast majority of people dealing with a typical sinus infection.
What Recovery Looks Like
Most acute sinus infections clear within 1 to 2 weeks, with or without antibiotics. You can expect the worst pressure and congestion to peak around days 3 through 5, then gradually ease. Some residual congestion and mild postnasal drip can linger for a few weeks after the infection itself has resolved.
If you find yourself getting three or four sinus infections per year, or if symptoms routinely drag on for months, it’s worth investigating structural or allergic factors that might be setting the stage. Recurrent and chronic sinusitis are treatable, but they usually require a more targeted approach than simply riding out each episode.