Most sinus infections are diagnosed based on your symptoms and how long you’ve had them, not through lab tests or imaging. A doctor will ask about the type of drainage you’re experiencing, whether your nose feels blocked, and whether you have facial pain or pressure. In most cases, that conversation plus a quick physical exam is enough to make the diagnosis and determine whether you need antibiotics.
The Symptom Criteria Doctors Use
Doctors follow a structured checklist rather than going on gut feeling. The standard diagnostic criteria require at least two major symptoms, or one major symptom plus two or more minor ones.
Major symptoms include:
- Cloudy or colored nasal discharge (from the front of the nose or dripping down the throat)
- Nasal congestion or blockage
- Facial pain, pressure, or fullness
- Reduced or lost sense of smell
- Fever
Minor symptoms include headache, ear pain or fullness, bad breath, dental pain, cough, and fatigue. None of these on their own point to a sinus infection, but when stacked on top of a major symptom, they strengthen the diagnosis.
The updated 2025 guidelines from the American Academy of Otolaryngology simplify this even further: you likely have acute sinusitis if you have cloudy or colored nasal drainage plus either a stuffy nose or facial pain and pressure, lasting up to four weeks.
How Your Doctor Tells Viral From Bacterial
This is the part that matters most for your treatment, because antibiotics only help bacterial infections. The distinction comes down to timing, not the color of your mucus.
A viral sinus infection is the most likely diagnosis if you’ve been sick for fewer than 10 days and your symptoms are gradually improving or at least holding steady. This is essentially a bad cold that settled into your sinuses, and it resolves on its own.
A bacterial sinus infection is suspected in two specific patterns. The first is persistence: your symptoms haven’t improved at all after 10 days. The second is called “double worsening,” where you start to feel better and then get noticeably worse again within those 10 days, with a new spike in fever, worsening congestion, or a return of thick discharge. Either pattern suggests bacteria have taken hold and antibiotics may be warranted.
What Happens During the Physical Exam
Your doctor will typically look inside your nose using a nasal speculum, a small handheld instrument that gently widens the nostril. They’re checking for swollen tissue, visible pus, and any structural issues like a deviated septum that could be contributing to poor drainage. Sometimes a decongestant spray is applied first to shrink the tissue and get a clearer view.
They’ll also press on and tap the areas over your cheekbones and forehead to check for tenderness, which can indicate inflammation in the maxillary or frontal sinuses. An older technique called transillumination involves shining a light against your cheek or under the brow ridge to see whether light passes through the sinus. A blocked or fluid-filled sinus won’t transmit light well. This method is simple but not highly reliable on its own.
When an Endoscope Is Used
If your symptoms are severe, recurring, or not responding to treatment, a doctor (often an ENT specialist) may use a thin, flexible tube with a camera called a nasal endoscope. This goes into the nasal passage and gives a direct view of the sinus drainage pathways.
The endoscope reveals redness, swelling, crusting, and most importantly, pus draining from specific openings. Where the pus appears tells the doctor which sinuses are infected. Pus draining from the middle part of the nasal passage typically comes from the cheek, forehead, or front sinus cavities. Pus appearing higher up and further back points to the sinuses behind the eyes or at the base of the skull. In one review, nasal endoscopy had 80% sensitivity and 94% specificity, making it significantly more accurate than a standard X-ray.
When Imaging Is Needed
For a straightforward sinus infection, imaging is not required. A CT scan won’t change your treatment if your symptoms clearly fit the clinical criteria and you’re responding normally.
CT scans become appropriate when something isn’t adding up: symptoms that don’t improve with treatment, unusually severe headaches, facial swelling, vision changes, or suspicion of a complication. The American College of Radiology’s guidelines note that uncomplicated sinusitis with typical inflammatory changes doesn’t need imaging, but complications like swelling around the eye, bulging of the eyeball, or nerve symptoms do warrant a scan to check for infection spreading beyond the sinuses.
Diagnosing Sinus Infections in Children
Children get diagnosed differently because they can’t always describe their symptoms clearly, and their sinus infections look less like the classic adult presentation. Kids rarely complain of facial pressure the way adults do. Instead, the hallmarks are a runny nose and daytime cough.
The American Academy of Pediatrics identifies three patterns that suggest bacterial sinusitis in children ages 1 to 18. Persistent symptoms, meaning nasal discharge of any color or a daytime cough lasting more than 10 days without improvement, are the most common trigger for diagnosis. A worsening course, where new symptoms or fever appear after initial improvement, is the second. The third is a severe onset: a fever of 102.2°F (39°C) or higher with thick, colored nasal discharge lasting at least three consecutive days.
The nasal discharge in children doesn’t have to be thick or green to count. Thin, clear drainage that simply won’t go away for more than 10 days is enough when paired with other symptoms. Bad breath, fatigue, headache, and poor appetite are common in kids with sinus infections but aren’t specific enough to make the diagnosis on their own.
Chronic and Recurrent Sinusitis
If your symptoms last longer than 12 weeks, the diagnosis shifts to chronic rhinosinusitis. This is a different condition from an acute infection. People with chronic sinusitis may have ongoing nasal blockage, persistent drainage, and dull facial pain even between flare-ups. Diagnosis typically involves nasal endoscopy and often a CT scan to assess the extent of inflammation and rule out structural problems like nasal polyps.
Recurrent acute sinusitis is diagnosed when you have multiple distinct episodes of acute infection but return to a healthy, symptom-free baseline between them. This pattern sometimes prompts further investigation into underlying causes like allergies, immune deficiencies, or anatomical issues.
Signs That Need Immediate Attention
Sinus infections can, in rare cases, spread to the eye socket or the brain. Swelling around the eye, especially at the inner corner, is the earliest warning sign and should be evaluated immediately. If the eyeball starts to protrude, if eye movement becomes limited, or if vision weakens, the infection has likely moved into the tissues surrounding the eye. These are emergencies. Untreated orbital infections can progress to a collection of pus behind the eye, which in turn can lead to blood clot formation in the veins near the brain or direct spread of infection into the skull. Constant, severe pain and an eye that is tender to touch are additional red flags that require urgent care.