A sinus infection typically announces itself with a combination of thick nasal discharge, facial pain or pressure, and congestion that lasts longer than a typical cold. Most colds improve within 7 to 10 days, so symptoms that persist beyond that window, or that get worse after initially improving, are the strongest signals that a sinus infection has developed.
The Core Symptoms
Sinus infections share several symptoms with colds and allergies, which is why they’re easy to confuse. But a few hallmarks tend to cluster together when your sinuses are genuinely infected:
- Thick, discolored nasal discharge. Yellow or green mucus draining from the nose or down the back of the throat is common, though color alone doesn’t confirm infection (more on that below).
- Facial pain and pressure. This often concentrates around the cheeks, forehead, or between the eyes, and it can worsen when you lean forward.
- Nasal congestion. Swollen sinus tissues block normal airflow, making it difficult to breathe through one or both nostrils.
- Reduced sense of smell and taste. Congested sinuses limit airflow to the smell receptors in your nose, which dulls your ability to taste food beyond basic sweet and salty.
- Bad breath. Infected mucus carries bacteria and drains down the back of the throat, producing a persistent foul smell that mouthwash won’t fix.
- Fever. Not always present, but a temperature above 100.4°F points toward a more significant infection.
European clinical guidelines suggest that having at least three of these signs, particularly when pain and discharge are worse on one side, raises suspicion for a bacterial sinus infection.
The Timeline Matters Most
Duration is the single most useful clue. A standard cold virus causes sinus inflammation and congestion, but it follows a predictable arc: symptoms peak around days 3 to 5 and then gradually improve. A sinus infection breaks that pattern in one of two ways.
The first is simple persistence. If your symptoms haven’t improved at all after 10 days, that’s a key threshold. The American Academy of Otolaryngology uses this 10-day mark as a primary diagnostic criterion for bacterial sinusitis.
The second pattern is called “double sickening.” You start feeling better after the initial cold, then around day 5 to 7 your symptoms suddenly worsen again. New facial pain appears, discharge gets thicker, or a fever returns. This rebound strongly suggests bacteria have moved into sinuses that were already inflamed by the original virus.
Viral vs. Bacterial: Does It Matter?
Viruses cause most sinus infections. This is worth knowing because it means most cases resolve on their own without antibiotics. A viral sinus infection looks and feels nearly identical to a bacterial one in the first week. The discharge can be just as thick and green, the pressure just as intense.
The practical difference comes down to timing and trajectory. Viral sinus infections improve steadily after the first week. Bacterial infections don’t, or they get worse. A fever lasting longer than 3 to 4 days also leans toward a bacterial cause. Your doctor will use these patterns, not a lab test or imaging scan, to decide whether antibiotics are warranted in most cases.
Green Mucus Doesn’t Mean Bacterial
This is one of the most persistent misconceptions. Green or yellow mucus feels like obvious proof of infection, but the color comes from enzymes released by white blood cells responding to any irritant, whether that’s a virus, bacteria, or even seasonal allergies. These enzymes contain iron, which gives mucus its greenish tint. Mucus that sits in your sinuses overnight becomes more concentrated and darker by morning, regardless of the cause.
Harvard Health has noted that mucus color and consistency cannot reliably distinguish a viral from a bacterial sinus infection. Allergies alone can produce thick yellow or green discharge with no infection present at all. So while discolored mucus is one piece of the puzzle, it’s not the deciding piece.
Sinus Infection vs. Allergies
Allergies and sinus infections overlap in congestion and runny nose, but they diverge in a few telling ways. The biggest differentiator is itching. Allergies make your eyes, nose, and throat itch. You sneeze in bursts. Your eyes water. A sinus infection rarely causes itching at all.
Facial pain and pressure point toward infection rather than allergies. So does fever. Allergies also tend to follow a seasonal or environmental pattern: symptoms flare when you’re exposed to pollen, dust, or pet dander, and they improve when you remove the trigger. A sinus infection gets steadily worse regardless of your environment.
That said, allergies can set the stage for a sinus infection. Prolonged allergic inflammation swells the sinus openings, traps mucus, and creates conditions where bacteria thrive. If your usual allergy symptoms suddenly shift to include one-sided facial pain, thicker discharge, or fever, an infection may have developed on top of the allergic irritation.
Acute vs. Chronic Sinusitis
Sinus infections fall into two main categories based on how long they last. Acute sinusitis lasts less than 4 weeks and is what most people experience: a cold that turns into sinus pressure, pain, and congestion before eventually clearing up.
Chronic sinusitis lasts longer than 12 weeks. The symptoms are often less intense than acute sinusitis but more persistent. Instead of sharp facial pain and high fever, chronic sinusitis tends to produce ongoing congestion, post-nasal drip, a dull sense of pressure, and a reduced sense of smell that lingers for months. Nasal polyps, structural issues in the nose, or recurring infections can all contribute to the chronic form. If you find yourself dealing with sinus symptoms that never fully resolve across multiple months, that’s a different condition from a one-off infection and typically requires a different treatment approach.
How Doctors Confirm It
For a straightforward acute sinus infection, diagnosis is almost entirely based on your symptoms and their timeline. There’s no routine blood test or scan involved. Your doctor will ask how long you’ve been sick, whether symptoms improved and then worsened, and where exactly the pain is located.
If your symptoms are chronic or keep coming back, your doctor may look inside your nasal passages with a thin, flexible camera called a nasal endoscope. This allows them to see swelling, polyps, or pus draining from specific sinus openings. In some chronic cases, a CT scan of the sinuses provides a more complete picture of what’s going on structurally. But for a typical first-time sinus infection, these tools aren’t necessary.
Warning Signs That Need Prompt Attention
Most sinus infections are uncomfortable but not dangerous. A few symptoms, however, signal that the infection may be spreading beyond the sinuses. Swelling or redness around the eye, vision changes, a severe headache that doesn’t respond to pain relievers, a stiff neck, or a high fever above 104°F all warrant same-day medical evaluation. These complications are uncommon but serious, as the sinuses sit close to the eyes and brain.