The most reliable sign of a sinus infection is thick, discolored nasal drainage that lasts longer than 10 days, combined with facial pressure or nasal congestion. A regular cold follows a predictable arc: you feel worst around days three to five, then gradually improve. A sinus infection either refuses to improve after 10 days or gets better and then suddenly worsens again. That pattern is the clearest signal that something beyond a common cold is going on.
The Core Symptoms
A sinus infection, technically called sinusitis, produces a specific cluster of symptoms. The hallmark is purulent nasal drainage, meaning thick, opaque mucus that drains from your nose or down the back of your throat. That drainage needs to be paired with at least one other symptom: either nasal congestion that makes it hard to breathe through your nose, or a feeling of pain, pressure, or fullness in your face, particularly around your cheeks, forehead, or between your eyes.
Facial pressure alone, without the thick nasal discharge, is not enough to point to a sinus infection. Plenty of other things cause facial pressure, including tension headaches and migraines. The drainage is the key piece.
Other common symptoms include a reduced sense of smell, ear pressure, upper tooth pain, fatigue, and a cough that worsens at night as mucus drips down the back of your throat.
The 10-Day Rule
Most colds are caused by viruses and clear up on their own within seven to 10 days. If your symptoms persist beyond that 10-day mark without improvement, the odds shift toward a bacterial sinus infection. This is the simplest and most widely used threshold for telling the two apart.
There’s a second pattern that’s even more telling. Sometimes you catch a cold, start to feel better around day five or six, and then suddenly get worse again, with renewed congestion, thicker drainage, and a return of facial pain or fever. Doctors call this “double sickening,” and it’s one of the strongest clinical indicators that bacteria have moved in. If you notice this rebound between days five and 10 of your illness, a bacterial sinus infection is the likely culprit.
Green Mucus Doesn’t Mean What You Think
One of the most persistent misconceptions is that yellow or green mucus means you have a bacterial infection and need antibiotics. This simply isn’t reliable. You cannot distinguish a viral from a bacterial sinus infection based on mucus color alone. Green mucus is produced when white blood cells release iron-containing enzymes to fight off any irritant, whether that’s a virus, bacteria, or even allergies. Seasonal allergies can produce thick, yellow-green discharge with no infection at all.
Mucus also darkens naturally when it sits still. That’s why your first nose blow in the morning often produces the greenest, thickest mucus of the day. It’s been concentrating in your sinuses overnight. This happens with ordinary colds just as much as with bacterial infections.
How It Looks Different in Kids
Children get sinus infections too, but they show up differently. Kids are less likely to complain about facial pressure and more likely to display a persistent cough (especially at night), bad breath, crankiness, and low energy. Swelling around the eyes is more common in children than in adults. A cold that lingers beyond 10 to 14 days, sometimes with a low-grade fever, is the typical presentation parents should watch for. Headache as a sinus symptom is uncommon in children younger than six.
Post-nasal drip in kids can also trigger a sore throat, nausea, and occasionally vomiting, which can make the whole picture look like a stomach bug rather than a sinus problem.
What Happens at the Doctor’s Office
Sinus infections are usually diagnosed based on your symptoms and a physical exam. There’s no routine test for a straightforward case. Your doctor will look inside your nose, ask about the timeline of your symptoms, and check for tenderness over your sinuses.
If your symptoms are severe, keep recurring, or don’t respond to treatment, your doctor may use a thin, flexible tube with a light on the end (an endoscope) to look directly inside your nasal passages and sinus openings. A CT scan can show detailed images of your sinuses but is typically reserved for complicated or chronic cases, not a first-time infection. Lab cultures of nasal tissue are rare and only used when infections won’t clear up or keep getting worse.
Acute vs. Chronic Sinusitis
An acute sinus infection lasts up to four weeks and is what most people experience after a bad cold. Chronic sinusitis is a different condition: it means you’ve had at least two of the core symptoms (thick drainage, congestion, facial pressure, or a reduced sense of smell) for 12 weeks or longer. Chronic sinusitis often involves ongoing inflammation rather than a single bacterial infection, and it requires a different treatment approach.
Some people cycle through repeated acute infections, which feels chronic but technically isn’t the same thing. If you’re getting three or four sinus infections a year, that pattern is worth investigating with your doctor, since structural issues or allergies may be contributing.
Symptoms That Need Immediate Attention
Most sinus infections are uncomfortable but not dangerous. A small number can spread to nearby structures, particularly the eye sockets and, in very rare cases, the brain. Go to an emergency room if you develop any of the following alongside your sinus symptoms:
- Swelling, redness, or pain around the eyes
- Double vision or other changes in eyesight
- High fever
- Stiff neck
- Confusion
These can signal that the infection has spread beyond the sinuses and requires urgent treatment. They’re uncommon, but recognizing them matters.