What are the differences between allergies and sinusitis?

Several: Sinusitis is inflammation of the sinuses due to infection, either from bacteria, viruses or fungi. The symptoms are similar to allergy in many ways include runny nose, sinus pressure, headache, congestion, postnasal drainage, and decreased sense of smell. Sinus infections may also lead to fever, while allergies never cause fever. Allergies are sensitivities to various proteins (pollen, mold, pets).