The four types of paranasal sinuses all connect to the nasal cavity via tiny openings, which are commonly referred to as ostia. These passageways can easily become clogged, which then disrupts the natural mucus draining process and can lead to the development of sinusitis. Sinusitis, in its most simplistic terms, can be defined as the term used to describe the condition when the mucus membranes of the sinuses get inflamed. The most common culprits of clogging the paranasal passageways are allergies (which cause allergic inflammations) and the common cold (which causes swelling of the nasal lining).
Sinusitis is commonly accompanied by other upper respiratory viral infections and, in most cases, doesn’t require any treatment. However, more severe cases of sinusitis can develop (which are called purulent, or pus-producing, sinusitis) which do require the use of antibiotic treatment. In some cases involving more chronic instances of sinusitis a more comprehensive treatment method (such as surgery) may be required.