Budesonide is a steroid. It prevents the release of substances in the body that cause inflammation. Budesonide nasal is used to treat nasal symptoms such as congestion, sneezing, and runny nose caused by seasonal or year-round allergies. Budesonide is also used to keep nasal polyps from coming back after surgery to remove them. Budesonide may also be used for purposes other than those listed in this medication guide.