Sinus is a term often used by laymen to describe a variety of separate but related conditions. Sinus is often used to describe symptoms including nasal congestion, pressure over the sinus region, post nasal drip and nasal discharge. In medical terms, sinus is usually synonymous with rhinitis. It is a condition characterized by inflammation involving the lining of the nose and sinus cavities. When associated with infection it is called sinusitis. Common reasons for sinus problems include allergies, low immune system, and anatomic variations. Some cases of sinusitis are often preceded by an upper respiratory tract infection or allergen exposure. For people with recurrent or chronic sinus problems, it is important to explore the potential cause in order to get better outcomes.