Allergies, deviated septums and sinus problems with nasal polyps are common causes of nasal obstruction. The septum is a wall that goes back the full length of the nasal passage dividing the inside of the nose into 2 equal passageways. If the septum is crooked, we call it deviated. A mild deviation will cause no problem breathing. The more crooked the septum is, the more it will block one or both sides of the nose. A crooked septum can be surgically corrected if the blockage is bad enough. A very common cause of nasal blockage is swelling of the linings of the nose by allergies. This can be seasonal or all year round depending on what causes the allergies. Pet dander would be all year while pollen would be seasonal. There are many ways to treat allergies including allergy pills, allergy sprays, avoidance of the allergy causing swelling and allergy desensitization. Nasal polyps are growths in the nose that usually come from the sinuses and project into the nose. The larger they are the more blockage they cause. Polyps can occur due to allergies or sinus disease amongst others. They are not cancerous like colon polyps might be. They may be treated with nasal sprays, allergy treatment, certain oral medications or surgery.