There is no quick at-home test for a sinus infection. Diagnosis is based almost entirely on your symptoms, how long they’ve lasted, and how they’ve changed over time. Most sinus infections are identified through a clinical evaluation rather than a lab test or scan, and understanding the specific symptom patterns doctors look for can help you figure out whether what you’re dealing with is a regular cold or something that needs treatment.
Symptom-Based Diagnosis Is the Standard
Sinus infections are diagnosed clinically, meaning your doctor evaluates your symptoms rather than ordering a test in most cases. According to guidelines from the American Academy of Otolaryngology, acute sinusitis is defined as up to four weeks of cloudy or colored nasal drainage plus at least one of the following: a stuffy or blocked nose, or pain and pressure in the face, head, or around the eyes.
But here’s the critical piece: most sinus infections are viral, not bacterial, and antibiotics only help with bacterial ones. The main way doctors distinguish between the two is time. A bacterial sinus infection is suspected when symptoms don’t improve at all within 10 days of getting sick, or when symptoms start to get better and then suddenly worsen. That second pattern, sometimes called “double sickening,” typically happens around five days in. You feel like you’re turning a corner, then congestion, pain, and drainage come roaring back. That rebound strongly suggests bacteria have taken hold on top of the original viral infection.
What You Can Assess at Home
You can’t confirm a sinus infection on your own, but you can track the details that matter most for diagnosis. Start paying attention to three things: how long your symptoms have lasted, whether they’re getting better or worse, and the color and consistency of your nasal discharge.
A typical cold causes congestion and even colored mucus for a few days, then gradually improves. If you’re past the 10-day mark with no improvement, or you experienced a clear improvement followed by a return of symptoms, those are the two patterns the CDC identifies as reasons to see a provider. Facial pain or pressure concentrated around the cheeks, forehead, or eyes (rather than a general headache) also points more toward sinusitis than a cold. Itchiness in the nose, eyes, or throat leans more toward allergies, while the scratchy, raw feeling in the back of the throat is more characteristic of a cold or sinus infection.
The Physical Exam
When you visit a doctor for a suspected sinus infection, the physical exam is straightforward. Your provider will look inside your nose with a light for swelling, redness, and discharge. They’ll also press gently on the skin over your sinuses to check for tenderness. This involves using the thumb to palpate just below the eyebrows along the bony ridge (over the frontal sinuses) and then below the cheekbones on either side of the nose (over the maxillary sinuses). Significant pain with light pressure suggests inflammation in those sinus cavities.
For most cases of acute sinusitis, this exam combined with your symptom history is enough for a diagnosis. No blood work, no imaging, no swabs. Your doctor is primarily listening to your timeline and looking at what’s happening inside your nose.
When Imaging Comes Into Play
CT scans of the sinuses are not routine for diagnosing a straightforward sinus infection, and guidelines specifically recommend against using them for acute cases. The reason is simple: CT findings are unreliable on their own. Up to 40% of adults with no sinus symptoms at all have abnormalities on sinus CT scans, and more than 80% of people with a common cold show sinus changes on imaging. A scan during a typical cold would look a lot like a scan during a bacterial sinus infection, making it nearly useless for telling the two apart.
CT scans become useful in specific situations: when symptoms are chronic (lasting 12 weeks or more), when infections keep coming back, when your doctor suspects a structural problem like a deviated septum or polyps, or when surgery is being considered. In those cases, the scan helps map the anatomy of your sinuses and identify blockages that might be driving recurrent problems.
Nasal Endoscopy
A nasal endoscopy involves a thin, flexible tube with a camera being guided into your nasal passages. It gives your doctor a direct view of areas that can’t be seen during a regular exam, including the narrow drainage pathways where sinuses empty into the nose. The procedure takes just a few minutes, and your nose is typically numbed with a spray beforehand.
During the endoscopy, your provider looks for swelling, polyps, and pus draining from specific sinus openings. Seeing pus coming from a particular sinus is one of the most direct visual confirmations of infection. If needed, the doctor can also collect a sample of that drainage for a culture, which identifies the exact bacteria involved.
Sinus Cultures and When They Matter
Most people with a sinus infection will never need a culture. Cultures are reserved for situations where standard antibiotic treatment has failed, when the infection is severe, or when complications are developing. The traditional gold-standard method involves puncturing the maxillary sinus with a needle to collect fluid directly, a procedure called antral puncture. It’s effective but painful and invasive, so it’s rarely used outside of research settings or complicated cases.
More commonly, if a culture is needed, your doctor will collect a sample during a nasal endoscopy by swabbing pus directly from the infected sinus drainage pathway. This approach is far less uncomfortable and still provides useful information about which bacteria are present, helping guide antibiotic choices when first-line treatment isn’t working.
Blood Tests Are Not Reliable
No blood test can reliably diagnose a sinus infection. C-reactive protein, a general marker of inflammation, is used as a point-of-care test in some countries but is not currently available for this purpose in the United States. Procalcitonin, a blood marker that helps distinguish viral from bacterial pneumonia, has not shown the same usefulness for sinusitis. Researchers have also explored using urine dipsticks to detect a marker called leukocyte esterase in nasal secretions, but this approach hasn’t been validated well enough for clinical use.
This is why symptom duration and pattern remain the primary diagnostic tools. Without a reliable quick test, the 10-day rule and the double sickening pattern are the best indicators available for separating bacterial infections from viral ones that will resolve on their own.
Sinus Infection vs. Allergies vs. a Cold
These three conditions overlap significantly, which is part of why diagnosing sinusitis can feel uncertain. All three can cause congestion, reduced sense of smell, and postnasal drip. A few distinguishing features help sort them out.
- Common cold: Symptoms typically peak around days 3 to 5 and then gradually improve. Colored mucus can appear briefly but clears up. A scratchy (not itchy) throat is common. The whole episode usually wraps up within 7 to 10 days.
- Allergies: Itchiness is the hallmark, affecting the nose, eyes, and sometimes the throat. Symptoms follow a pattern tied to triggers like pollen seasons or dust exposure. Nasal discharge tends to be clear and watery. There’s no fever.
- Bacterial sinus infection: Facial pain and pressure are more prominent than with a cold. Thick, discolored discharge persists beyond 10 days or returns after initial improvement. Fever is possible but not always present. Reduced sense of smell is common.
Loss of smell can occur with both allergies and sinusitis, since both cause swelling that blocks the smell receptors high in the nasal cavity. But persistent facial pressure concentrated around the cheeks or forehead, combined with prolonged or worsening symptoms, is the combination that most reliably points to a sinus infection rather than the alternatives.