A sinus infection (sinusitis) happens when the lining of your sinus cavities becomes inflamed and fills with mucus, creating a good environment for germs to grow. This usually starts with something that blocks normal drainage of mucus from the sinuses.
Main ways you get one
- Viruses from colds or flu are the most common cause; a regular upper respiratory infection can swell the nasal passages, block drainage, and lead to sinusitis.
- Bacteria can cause a sinus infection, often after a viral illness has already blocked the sinuses for about a week or more.
- Less often, fungi can infect the sinuses, mainly in people with weakened immune systems or certain chronic sinus problems.
Triggers that block sinuses
- Allergies (like hay fever, dust, or pollen) inflame the nasal lining and can keep mucus from draining, which increases the risk of infection.
- Structural issues such as a deviated septum, nasal polyps, or narrowed sinus openings make it physically harder for mucus to drain, so infections occur more easily or more often.
- Irritants like cigarette smoke, air pollution, and very dry air can irritate or dry out sinus linings, leading to swelling, cracking, and higher susceptibility to infection.
Risk factors in everyday life
- Having frequent colds, seasonal allergies, or asthma raises the chances of getting sinus infections repeatedly.
- A weak immune system (from illnesses or medications) makes it easier for viruses, bacteria, or fungi to cause sinusitis.
- Certain activities or exposures, like cigarette smoking or regular exposure to strong chemical fumes, increase irritation and inflammation in the sinuses.
Is it contagious?
- The sinus infection itself is not usually what spreads, but the viruses that cause most sinus infections (cold or flu viruses) can spread from person to person through coughs, sneezes, or contaminated hands.
- If you catch one of these respiratory viruses and your sinuses become swollen and blocked, you may then develop a sinus infection as a complication.
What you can do to lower risk
- Avoid smoking and secondhand smoke, and limit exposure to strong fumes or pollutants where possible.
- Manage allergies with medical advice (like allergy medicines or nasal sprays) to keep nasal passages less inflamed.
- Use humidified air and stay well hydrated to keep nasal mucus thin, which helps sinuses drain and may reduce infection risk.
