Sinusitis

Sinusitis is the inflammation of the sinuses. It's one of the most commonly suffered diseases in the world, with close to 10% of the population suffering from it at some time during any given year. Its primary cause is a viral infection, with most of the remaining cases being the result of an allergy. In rare cases, it has an autoimmune cause.
Most cases of sinusitis are acute and self-resolving. However, chronic sinusitis is not uncommon and may require less conservative treatment.
In most cases, treatment of the underlying cause will provide relief from the symptoms. Irrigation of the nasal passages with saline is also safe and effective. Decongestants should be avoided except when used for a short period of time as they can make the condition worse with long term use.
Sinusitis at Wikipedia