Sinusitis is diagnosed primarily through your symptoms and how long they’ve lasted, not through lab tests or scans. Most cases are identified in a standard office visit where your doctor evaluates your symptom pattern against established clinical criteria. Imaging and other tools come into play only when symptoms are severe, don’t respond to treatment, or have lasted 12 weeks or longer.
The Symptoms That Drive a Diagnosis
Doctors use a structured checklist to determine whether your symptoms add up to sinusitis. The standard approach, drawn from Infectious Diseases Society of America guidelines, requires either two major symptoms or one major symptom plus at least two minor ones.
The major symptoms are:
- Thick, discolored nasal discharge
- Nasal congestion or obstruction
- Facial congestion, fullness, pain, or pressure
- Reduced sense of smell
- Fever
Minor symptoms include headache, ear pain or pressure, bad breath, dental pain in the upper teeth, cough, and fatigue. None of these alone points to sinusitis, but stacked alongside a major symptom, they help complete the picture. Your doctor will ask detailed questions about where you feel pressure, what your nasal discharge looks like, and how long this has been going on.
What Happens During the Physical Exam
The most important finding your doctor looks for is visible pus in the nasal passages. This can be spotted with anterior rhinoscopy, where a small handheld instrument opens the nostril for a direct look inside, or by checking the back of the throat for postnasal drainage. If pus is present, it strongly supports a sinusitis diagnosis.
Your doctor may also press on the areas over your sinuses (cheekbones, forehead, between the eyes) to check for tenderness, though this alone isn’t enough to confirm the diagnosis. In straightforward cases, the combination of your reported symptoms and visible nasal discharge is sufficient.
If your sinusitis hasn’t improved with treatment, or if your doctor suspects a structural problem like polyps or a deviated septum, nasal endoscopy may be the next step. This involves passing a thin, flexible tube with a camera into the nasal cavity for a much more detailed view. Doctors specifically look at a small crescent-shaped groove called the hiatus semilunaris, located just behind the middle part of the nasal passage. In bacterial sinusitis, pus typically drains from this area, and the endoscope can reveal blockages that a basic exam would miss.
Bacterial vs. Viral: How Doctors Tell the Difference
This distinction matters because most sinusitis starts as a viral infection (essentially a bad cold) and clears on its own. Antibiotics only help if bacteria are involved, so doctors rely on three specific timing patterns to identify bacterial sinusitis:
- Persistent symptoms: Congestion, discharge, or facial pain lasting 10 days or more without any improvement.
- Severe onset: A fever of 102°F or higher along with thick nasal discharge and facial pain that persists for three to four consecutive days.
- Double worsening: Symptoms that seem to improve after four to seven days, then suddenly get worse again. This “double sickening” pattern is a hallmark of a bacterial infection taking hold after the initial virus.
If none of these patterns fit, the infection is almost certainly viral. Your doctor won’t order tests to confirm this. The timing of your symptoms is the test.
When Imaging Is Used
CT scans are not part of a routine sinusitis diagnosis. For a typical case of acute sinusitis, imaging adds little to what your doctor already knows from your symptoms and exam. Plain X-rays are even less useful and largely considered outdated for this purpose.
CT scans become relevant when sinusitis has lasted 12 weeks or longer, when treatment has failed, or when your doctor suspects complications like the infection spreading beyond the sinuses. A CT scan can show thickened sinus linings, fluid levels, and blockages in the drainage pathways. If surgery is being considered, a CT scan is essential for mapping the anatomy of your sinuses beforehand.
Diagnosing Chronic Sinusitis
Chronic rhinosinusitis is defined as sinus inflammation lasting 12 weeks or longer. The bar for diagnosis is higher than for an acute episode. Symptoms alone aren’t enough. Doctors need objective evidence of ongoing mucosal inflammation, which means either a CT scan showing sinus changes or a nasal endoscopy revealing polyps, swelling, or discharge.
This two-part requirement (symptoms plus visual or imaging confirmation) exists because many conditions can mimic chronic sinusitis for months. Without objective proof of sinus inflammation, the diagnosis doesn’t hold.
In chronic cases that keep flaring up or don’t respond to antibiotics, your doctor may take a culture directly from inside the nasal passages using an endoscope. This identifies the specific bacteria or fungi involved so treatment can be targeted rather than guessed at. Older methods involved puncturing the maxillary sinus with a needle to collect fluid, but most specialists have moved away from this because endoscopic cultures from the sinus drainage pathways are more comfortable and often more accurate.
How It’s Diagnosed in Children
Children get sinusitis frequently, but the diagnosis looks slightly different. Kids are less likely to report facial pressure or smell changes, so doctors rely heavily on three patterns outlined by the American Academy of Pediatrics. The most commonly used criterion is nasal congestion or cough lasting more than 10 days without improvement. Doctors also watch for a worsening of typical cold symptoms around days five to seven, or a severe onset with thick, discolored discharge for at least three consecutive days.
Imaging is generally avoided in children with uncomplicated acute sinusitis. A CT scan exposes a child to radiation and frequently shows sinus changes during ordinary colds, leading to overdiagnosis.
Ruling Out Migraine
One of the biggest diagnostic pitfalls is confusing migraine with sinus headache. The overlap is striking: 45% of people with migraine experience nasal congestion or watery eyes during an attack, because the nerves activated during a migraine are the same ones that supply the sinuses, eyes, and teeth. Weather changes, commonly blamed for “sinus headaches,” are actually a well-known migraine trigger.
A few features help separate the two. True sinus headaches come with thick, discolored nasal discharge and typically involve fever or a reduced sense of smell. Migraine pain tends to be pulsating, worsens with physical activity, and often brings nausea, vomiting, or sensitivity to light, noise, and smells. If your “sinus headaches” keep coming back but never produce colored discharge or fever, migraine is worth discussing with your doctor.
When Allergy Testing Plays a Role
If sinusitis keeps returning or becomes chronic, your doctor may investigate whether allergies are fueling the inflammation. Persistent allergic reactions cause ongoing swelling in the nasal passages, which blocks sinus drainage and creates conditions for repeated infections.
The two main options are skin prick testing, where small amounts of common allergens are applied to the skin, and blood tests that measure levels of the antibody your immune system produces in response to specific allergens. Current blood tests have caught up to skin testing in accuracy and are particularly practical in a primary care setting. Identifying a specific trigger (dust mites, mold, pet dander, pollen) can shift treatment from repeatedly treating infections to preventing them by managing the underlying allergy.