You don’t catch a sinus infection the way you catch a cold, though a cold is usually what starts one. Sinus infections themselves aren’t directly passed from person to person. Instead, they develop when something blocks the drainage pathways in your sinuses, trapping fluid that becomes a breeding ground for germs. The vast majority of the time, that “something” is a virus you picked up from another person.
What Actually Causes a Sinus Infection
Your sinuses are air-filled pockets behind your forehead, cheeks, and eyes. They stay healthy by draining mucus through small openings into your nasal cavity. A sinus infection develops when those openings get blocked, fluid accumulates, and germs start multiplying in the trapped mucus.
The most common trigger is a viral upper respiratory infection like the common cold or flu. When you get a cold, the mucous membranes lining your nasal passages swell, physically blocking the sinus openings. Once sealed off, air inside the sinuses gets absorbed into the bloodstream, creating a pressure drop that pulls more fluid in. That stagnant fluid is the perfect environment for bacteria or other pathogens to thrive. Your immune system responds by sending white blood cells and even more fluid to fight the infection, which increases pressure and pain.
Between 90% and 98% of acute sinus infections are caused by viruses and resolve on their own without antibiotics. Only about 0.5% to 2% of viral sinus infections in adults progress to a secondary bacterial infection. In children, that number is higher, around 5% to 10%.
How the Underlying Viruses Spread
The viruses that lead to sinus infections are highly contagious. They spread through respiratory droplets when an infected person coughs, sneezes, or talks. You can also pick them up by touching a contaminated surface (a doorknob, phone, or countertop) and then touching your nose or mouth.
So while the sinus infection itself isn’t what passes between people, the cold virus that triggers it absolutely is. If someone near you has a sinus infection that started with a cold, their virus can spread to you and give you the same cold. Whether that cold then turns into a sinus infection depends on your own anatomy, immune response, and other risk factors.
Allergies as a Trigger
Allergies are the second most common pathway to a sinus infection. Allergic reactions cause the same type of mucous membrane swelling that a cold does, blocking sinus drainage and setting up the same chain of events. Roughly 60% of people with chronic sinus problems have allergies to environmental triggers like pollen, dust mites, or mold, compared to 30% to 40% of the general population.
In some cases, fungal spores in the sinuses can germinate in trapped mucus, intensifying the allergic response and creating a cycle of inflammation that’s difficult to break. This is less common than standard allergy-driven sinusitis but helps explain why some people develop recurring infections during allergy season.
Structural and Environmental Risk Factors
Some people are simply more prone to sinus infections because of the physical shape of their nasal passages. A deviated septum, nasal polyps, or naturally narrow sinus openings can make drainage difficult even without a cold or allergies. Nasal polyps in particular tend to cluster in people who also have asthma, hay fever, or cystic fibrosis, and genetics can influence how your nasal tissues respond to inflammation.
Environmental irritants play a role too. Dry air dries out mucus, making it thicker and harder to drain. Cigarette smoke, air pollution, and airborne chemical irritants can damage the tiny hair-like structures (cilia) that sweep mucus out of your sinuses. When those cilia stop working efficiently, fluid sits longer and infection becomes more likely.
How to Tell if a Cold Has Become a Sinus Infection
Since most sinus infections start as colds, the tricky part is knowing when you’ve crossed the line. Clinical guidelines point to three patterns that suggest a bacterial sinus infection rather than a lingering cold:
- Persistent symptoms: Congestion, facial pressure, or nasal discharge lasting 10 days or more without improvement.
- Severe onset: A fever of 102°F or higher along with thick, discolored nasal discharge or intense facial pain for at least three consecutive days at the start of illness.
- Double sickening: You start to feel better after a few days, then symptoms come back worse around day five or six, with a new fever, increased headache, or worsening discharge.
If your symptoms follow a typical cold pattern (peaking around days three to five, then gradually improving) you almost certainly have a viral infection that will resolve on its own.
Reducing Your Risk
Because most sinus infections trace back to a cold virus, basic hygiene is the most effective prevention. Wash your hands frequently, avoid touching your face, and keep distance from people with active cold symptoms.
Beyond avoiding viruses, keeping your sinuses draining well is key. Saline nasal rinses flush out allergens, irritants, and excess mucus before they can cause blockages. Some people use them daily or a few times a week as a preventive habit, not just when they’re already congested. A humidifier can help if you live in a dry climate or spend a lot of time in heated indoor air, keeping mucus thin enough to drain naturally. Managing allergies with appropriate treatment also reduces the chronic swelling that makes sinus infections more likely in the first place.