Most sinus infections are diagnosed based on your symptoms and how long they’ve lasted, not through scans or lab tests. The key question isn’t whether your sinuses are inflamed (they almost certainly are if you have a cold), but whether the infection is bacterial and needs treatment or viral and will clear on its own. Doctors use three specific symptom patterns to make that call.
Viral Cold vs. Bacterial Sinus Infection
Nearly every cold causes some degree of sinus inflammation. Your sinuses swell, mucus builds up, and your face feels heavy. That’s viral sinusitis, and it resolves on its own. A bacterial sinus infection develops when that swelling traps bacteria in the sinus cavities, creating a secondary infection on top of the original cold. The challenge is telling the two apart, because early symptoms look identical.
The most reliable way to distinguish them is time. A typical viral cold peaks around days three to five, then gradually improves. If your symptoms haven’t improved at all after 10 days, the infection is more likely bacterial. But duration isn’t the only marker. Three distinct patterns point toward a bacterial cause:
- Persistent symptoms: Nasal congestion, discharge, or facial pressure lasting 10 days or more with no signs of improvement.
- Severe onset: A fever of 102°F (39°C) or higher along with thick, discolored nasal discharge and facial pain, lasting at least three consecutive days from the start of illness.
- Double sickening: You start to feel better after five or six days, then suddenly get worse again with new fever, increased discharge, or worsening headache.
If your symptoms fit one of these three patterns, your doctor will typically diagnose a bacterial sinus infection on that basis alone. No imaging, no lab work, no swabs.
What Happens During a Physical Exam
When you visit a doctor for suspected sinusitis, the exam is straightforward. Your doctor will look inside your nose for swollen tissue and discharge, then press on specific areas of your face to check for tenderness. To evaluate the frontal sinuses, they’ll press along the bony ridge just below your eyebrows. For the maxillary sinuses (the large ones behind your cheekbones), they’ll press beneath the lower edge of the cheekbone on each side. Pain or tenderness during this palpation supports the diagnosis, though it’s not definitive on its own.
Not all sinuses can be examined this way. The ethmoid sinuses (between your eyes) and sphenoid sinuses (deep behind your nose) can’t be directly evaluated through a physical exam. If your doctor suspects infection in these deeper sinuses, or if your symptoms keep recurring, they may refer you to an ear, nose, and throat specialist for nasal endoscopy, a procedure where a thin, flexible scope is passed into the nose to look directly at the sinus openings and check for pus or swollen tissue.
When Imaging Is Needed
For a straightforward sinus infection, X-rays and CT scans aren’t necessary. Uncomplicated sinusitis does not require imaging, and getting a scan during an ordinary cold would almost always show sinus inflammation, which doesn’t help distinguish viral from bacterial infection.
CT scans become useful in specific situations: sinusitis that keeps coming back, symptoms that don’t respond to treatment, or suspected complications like an infection spreading toward the eye socket or brain. A standard noncontrast CT scan is usually sufficient. If your doctor suspects a serious complication such as an abscess or infection around the eye, a contrast-enhanced scan provides more detail. Imaging also plays a role before sinus surgery, mapping the anatomy so the surgeon knows what they’re working with.
When Cultures Are Taken
Routine swabs and cultures aren’t part of a standard sinus infection diagnosis. Most bacterial sinus infections respond to first-line treatment, making it unnecessary to identify the exact bacteria involved. A culture is selectively obtained in people at high risk of complications or antibiotic resistance, such as those with weakened immune systems or infections that haven’t responded to multiple rounds of treatment.
When a culture is needed, the preferred method is sinus aspiration, where a specialist uses a needle or endoscope to collect fluid directly from the sinus cavity. A simple nasal swab isn’t ideal because it picks up bacteria normally living in the nose, making results unreliable. This procedure is performed by an ENT surgeon and is reserved for complicated or treatment-resistant cases.
Diagnosing Sinus Infections in Children
Children get diagnosed using the same three symptom patterns as adults, with some differences in how the illness presents. Kids with bacterial sinusitis are less likely to complain of facial pain or headache. Instead, the hallmark signs are persistent nasal discharge of any color (not just green or yellow) and a daytime cough lasting more than 10 days without improvement. Worsening symptoms after initial improvement, or a high fever with thick discharge for three or more days, also point toward a bacterial cause.
The American Academy of Pediatrics specifically recommends against imaging to diagnose sinus infections in children. Scans can’t reliably tell the difference between a viral and bacterial infection in kids, and the findings rarely change the treatment plan. The exception is when a child shows signs of a complication spreading beyond the sinuses, particularly toward the eyes or brain, where a contrast-enhanced CT scan is warranted.
Sinus Infection vs. Migraine
Many people who think they have recurrent sinus infections actually have migraines. This isn’t a small overlap. True sinus headaches, caused by an active infection, are rare compared to migraines that mimic sinus pressure. Both can cause facial pain, pressure around the eyes, and even nasal congestion.
The distinguishing features are specific. A genuine sinus headache comes with thick, discolored nasal discharge, reduced sense of smell, and sometimes fever. The pain should resolve within seven days after the infection clears. Migraines, on the other hand, cause throbbing or pounding head pain that worsens with physical activity, along with nausea, vomiting, or sensitivity to light, noise, and smells. If your “sinus headaches” come and go without the telltale thick discharge and fever, migraine is the more likely explanation.
Red Flags That Need Urgent Attention
Sinus infections very rarely spread beyond the sinuses, but when they do, the complications are serious. The sinuses sit close to the eye sockets and the brain, so an aggressive infection can reach these areas. Watch for swelling or redness around one eye, vision changes, severe headache that’s distinctly worse than typical sinus pressure, high fever that develops after days of illness, or confusion and neck stiffness. These symptoms suggest the infection may be spreading to the tissue around the eye (orbital cellulitis) or toward the brain, and they require emergency evaluation with imaging.