A sinus infection is inflammation or swelling of the tissue lining your sinuses, the air-filled cavities in your face. Nearly 29 million adults in the United States have been diagnosed with sinusitis, making it one of the most common reasons people visit a doctor. Most sinus infections start with a virus and clear up on their own, but understanding what’s happening in your body helps you know when to wait it out and when something more is going on.
Where Your Sinuses Are
You have four pairs of sinuses, one on each side of your face. Your frontal sinuses sit in your forehead above your eyebrows. Your ethmoid sinuses are between your eyes, behind the bridge of your nose. Your sphenoid sinuses are deeper in your skull, behind your eyes. Your maxillary sinuses, the largest pair, are in the bones of your upper jaw beneath your cheeks.
These cavities are lined with a thin, moist tissue that produces mucus. Under normal conditions, that mucus drains freely through small openings into your nasal passages. When those linings swell, the openings narrow or close off entirely, trapping mucus inside. That trapped mucus creates the pressure, pain, and congestion you feel during a sinus infection.
What Causes Sinus Infections
The vast majority of sinus infections are viral. Between 90% and 98% of cases are caused by the same viruses responsible for the common cold. A cold inflames the sinus linings, blocks drainage, and creates the perfect environment for mucus to build up. This is why sinus infections so often follow a few days of cold symptoms.
Only about 2% to 10% of sinus infections are bacterial. When bacteria are involved, the two most common types account for over half of all cases. Bacterial sinus infections typically develop as a secondary complication, meaning a viral infection comes first and bacteria move in afterward when mucus has been sitting stagnant in the sinuses. Allergies, nasal polyps, a deviated septum, and anything else that blocks normal drainage can also set the stage for infection.
Common Symptoms
The hallmark symptoms of a sinus infection include:
- Stuffy or runny nose that persists beyond typical cold duration
- Facial pain or pressure, often felt in the cheeks, forehead, or between the eyes depending on which sinuses are affected
- Headache, usually worse when bending forward
- Post-nasal drip, mucus running down the back of your throat
- Sore throat from that constant drainage
- Cough, often worse at night
- Bad breath caused by bacteria in trapped mucus
The location of your facial pain often corresponds to the sinuses that are inflamed. Pressure across your forehead points to the frontal sinuses. Pain in your cheeks or upper teeth suggests the maxillary sinuses. A deep ache behind your eyes can involve the sphenoid or ethmoid sinuses.
Viral vs. Bacterial: How to Tell the Difference
This is the question that matters most for treatment. A viral sinus infection typically follows the arc of a cold: symptoms peak around days three to five, then gradually improve. The whole episode usually resolves within 10 days. Mucus color alone is not a reliable indicator. Yellow or green mucus is common with viral infections too, as your immune system’s white blood cells give the discharge its color.
A bacterial infection is more likely if your symptoms last longer than 10 days without improving, if you have a high fever (above 102°F) along with facial pain and thick nasal discharge for three or more consecutive days, or if your symptoms improve and then suddenly worsen again. That “double worsening” pattern, where you start feeling better then take a sharp turn, is one of the strongest clues that bacteria have entered the picture.
Acute, Subacute, and Chronic Sinusitis
Sinus infections are classified by how long they last. Acute sinusitis is the most common type and typically resolves within 10 days, though it can linger for up to four weeks. Subacute sinusitis falls in the four-to-twelve-week range, representing a slower recovery that hasn’t quite tipped into chronic territory.
Chronic sinusitis is defined as symptoms lasting 12 weeks or more. This is a different condition from a standard sinus infection. It often involves persistent low-grade inflammation rather than an active infection, and it can be driven by allergies, nasal polyps, immune system issues, or structural problems in the nasal passages. About 11.6% of American adults have been diagnosed with chronic sinusitis, so it’s far from rare.
How Sinus Infections Are Treated
Because the overwhelming majority of sinus infections are viral, antibiotics won’t help most people. Antibiotics target bacteria and have no effect on viruses. Taking them unnecessarily contributes to antibiotic resistance and exposes you to potential side effects for no benefit. For a straightforward viral sinus infection, the goal is managing symptoms while your immune system does the work.
Antibiotics become appropriate when there’s strong evidence of a bacterial infection, based on the timing and severity patterns described above. Even then, a period of watchful waiting is often reasonable for mild cases, since some bacterial sinus infections resolve without antibiotics.
Home Remedies That Actually Help
Saline nasal irrigation is the best-supported home treatment. Using a neti pot, squeeze bottle, or nasal spray, you flush saline solution into one nostril and let it drain out the other, physically washing mucus and irritants from your nasal passages. One well-designed study found that people with chronic sinus symptoms who used a 2% saline rinse daily had a 64% improvement in overall symptom severity compared to standard care alone. The American Academy of Family Physicians rates saline irrigation as an effective add-on therapy for chronic sinusitis symptoms.
If you’re making your own saline rinse, use distilled, sterile, or previously boiled water. Tap water in the United States is generally considered safe for this purpose, but using treated water eliminates any risk of introducing harmful organisms into your sinuses. A basic solution uses about a quarter teaspoon of non-iodized salt per cup of water, though concentrations ranging from 0.9% to 3% have all been used safely.
Beyond nasal irrigation, staying well hydrated helps thin mucus. Warm compresses across your face can ease pressure. Sleeping with your head slightly elevated encourages drainage. Over-the-counter pain relievers can reduce headache and facial pain. Decongestant sprays provide short-term relief but should not be used for more than three days, as they can cause rebound congestion that makes things worse.
Warning Signs of Complications
Serious complications from sinus infections are uncommon but worth knowing about. Because your sinuses sit close to your eyes and brain, an infection that spreads beyond the sinus walls can become dangerous. Swelling or redness around one eye, changes in vision, severe headache that worsens rapidly, high fever that doesn’t respond to treatment, or a stiff neck are all signs that the infection may have moved into the tissue around the eye (orbital cellulitis) or toward the brain. These situations require immediate medical attention and typically involve imaging and stronger treatments in a hospital setting.
The risk is higher in young children, people with weakened immune systems, and anyone with an unusually severe or prolonged infection that hasn’t been evaluated.