What sort of problem is acute sinusitis?

Infection : Acute sinusitis is an infection of the nasal sinuses (maxillary, frontal, ethmoid, or sphenoid) that is of recent onset. This infection is usually of bacterial origin, but could also be due to a viral or fungal infection as well. Common symptoms include nasal congestion, foul odor from the nose, cough, facial or upper teeth pain, and a "sinus" headache. See your doctor if you have these symptoms.

Infection: "sinusitis" refers to inflammation of the sinuses. When it is "acute", it is due to infection. Most sinus infections are viral, but if the sinus pressure and colored secretions have been present for longer than two weeks, it is likely bacterial. Chronic sinusitis is often due to allergies or reflux; if left untreated, people with chronic sinusitis are at greater risk of frequent acute infections.