Sinusitis is an inflammation, or swelling, of the tissue lining the sinuses. It can happen to anyone. However, people with nasal allergies, nasal polyps, asthma and abnormal nose structures are all more likely to get sinusitis. It can be difficult to tell the difference between a cold, allergies, and a sinus infection. The common cold typically lasts a few days to a week. A cold can transform into a sinus infection. If you have a runny nose, stuffy nose or sinus pressure that lasts for more than 10 days, suspect an infection and see your doctor.